Merge remote-tracking branch 'origin/master' into codex/simp-session-dead-surface

# Conflicts: # docs/cordis-catalog/services.md # packages/core/session/README.md # packages/core/session/tests/derived-cache.spec.ts # packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts # packages/session-persistence/session-persistence/src/coordinator.ts # packages/session-persistence/session-persistence/src/index.ts
2026-07-14 17:24:02 +08:00
parent 60260b5d5b fb126e164a
commit 34a059c9bc
562 changed files with 4437 additions and 12564 deletions
@@ -10,7 +10,7 @@ The harness needs one internal language for messages that the loop, session log,

 Own the vocabulary: messages are arrays of typed content blocks (`text`, `reasoning`, `tool-call`, `tool-result`), with the union derived from the merge-extensible `ContentBlockMap` so plugins add block types via declaration merging. The same merge-extensible-map pattern types every "stringly" field (`MessageSource`, `FinishReason`, `TurnTrigger`, `TurnEndReason`). Streaming is a raw chunk protocol; `BlockAssembler` is the single shared assembly implementation. Adapters translate to provider wire formats — mapping cost lives in adapters, where it belongs.

-In-session context injection (`context/message`, `steering/message`) renders as tagged user-role envelopes (the system-reminder pattern) rather than a new role, so adapters carry zero burden. Live-adapter review has since validated the tagged-envelope rendering against current DeepSeek behavior; a future provider-specific mismatch should be handled in that adapter rather than by adding a new role to the canonical content vocabulary.
+In-session context injection (`context/message`, `steering/message`) renders as tagged user-role envelopes (the system-reminder pattern) rather than a new role, so adapters carry zero burden. Live-adapter validation confirms this rendering for current DeepSeek behavior; a future provider-specific mismatch belongs in that adapter rather than a new canonical role.

 ## Alternatives considered

@@ -19,6 +19,8 @@ In-session context injection (`context/message`, `steering/message`) renders as

 ## Consequences

- Reasoning has a home without provider contortions. Multimodal content deliberately has NO core block type: the core set is limited to blocks every shipping path honors, and a multimodal feature adds its block type through the merge-extensible map in the same coordinated change that maps it in the adapters, surfaces it in the UI bridges, and prices it in compaction — see [the drop-image RFC](../simplification/2026-07-04-drop-image-content-block.md). Block cache hints likewise have no core field: DeepSeek prompt caching is automatic, so no shipping adapter can transmit a hint; a caching feature adds a `cache` field together with the adapter that honors it — see [the producer-less-variants RFC](../simplification/2026-07-04-prune-producerless-vocabulary-variants.md). Assistant-prefix continuation (prefill) likewise has no request field: DeepSeek's chat-prefix completion is a Beta feature on a base URL neither shipping adapter targets, so a prefill feature adds `GenerateOptions.prefill` together with the adapter that honors it — see [the inert-request-knobs RFC](../simplification/2026-07-04-drop-inert-request-knobs.md).
+- Reasoning has a core home without provider-specific shapes.
+- Multimodal blocks return only with coordinated adapter, UI, and compaction support; see [the drop-image RFC](../simplification/2026-07-04-drop-image-content-block.md).
+- Cache hints and assistant prefill remain absent until a shipping adapter can honor them; see the [producer-less variants](../simplification/2026-07-04-prune-producerless-vocabulary-variants.md) and [inert request knobs](../simplification/2026-07-04-drop-inert-request-knobs.md) RFCs.
 - Every adapter pays a translation cost; the first real adapters have since validated the streaming protocol, and new adapters should continue proving their provider-specific mapping in adapter-local tests.
 - IDs that cross package boundaries are branded (`CallId`, `SessionId`, `AgentId`) — nominal typing at zero runtime cost.
@@ -4,7 +4,7 @@ Status: implemented

 ## Problem

-Tool parameters must reach the model as standard JSON Schema (the wire format), and tool authors deserve typed `execute(args)` without casts. The repo already vendors schemastery (used for plugin Config), so reusing it was the obvious candidate. The user also explicitly preferred per-property `required: true` booleans over JSON Schema's separate `required` array.
+Tool parameters must reach the model as standard JSON Schema while giving tool authors typed `execute(args)` without casts. Schemastery already serves plugin config, but the tool-author API needs per-property `required: true` booleans rather than JSON Schema's separate `required` array.

 ## Decision

@@ -18,4 +18,4 @@ A small custom DSL in dsh-tools: `SchemaSpec` (per-property specs with `required

 - First-party tool authors get zero-cast typed args; the type gymnastics cost stays inside the core package (sanctioned by the AGENTS.md type-safety policy).
 - The DSL is deliberately small (string/number/boolean/object/array, enum, default, nested properties/items). Gaps vs full JSON Schema (unions, formats, constraints) are accepted until real tools demand them.
- The InferArgs mapping is regression-tested at the type level (expectTypeOf) after an early optionality bug shipped and was caught by review.
+- The `InferArgs` mapping is regression-tested at the type level after an early optionality bug.
@@ -12,7 +12,7 @@ A `Session` is an append-only log of typed `SessionEvent`s — the single source

 Appends are synchronous (the hot path never blocks on I/O); `session/event` is a sync notification; persistence plugins buffer write-behind and drain at the awaited `session/flush` checkpoint fired at every turn end.

-Ordering contract: the loop appends to the session *before* emitting the corresponding Cordis event, and the `agent/step-result` waterfall runs before the `assistant/message` append so the log records what tool dispatch actually used (post-review fix; regression-tested).
+Ordering contract: the loop appends to the session *before* emitting the corresponding Cordis event, and the `agent/step-result` waterfall runs before the `assistant/message` append so the log records the message tool dispatch actually used. Regression tests pin that ordering.

 ## Alternatives considered

@@ -6,8 +6,6 @@ Status: implemented

 Failures crossed seams as bare strings. A tool error flattened to a text block — name, code, and stack lost — so a future sandbox/retry plugin couldn't tell ENOENT from EACCES, and the model got less actionable feedback than it could. A non-Error throw degraded further: the loop wrapped it in `new Error(String(x))`, dropping any code. And `LlmError` was the only typed error in the system, with no shared base, so there was nothing for a consumer to `instanceof` against generically.

-This is the last of the runtime-validation / error-taxonomy pieces and the one the user was most skeptical of, so it was deliberately built **last and in isolation**: the earlier PRs (arg validation, dev invariants) threw plain `Error`s with a `code` field, decoupled from any shared base, so this change is a pure upgrade and is independently revertible without unpicking them.
-
 ## Decision

 A single `HarnessError extends Error` base in `dsh-llm` (the leaf package every other imports — no new dependency edge): a stable `code` distinct from `message`, `cause` chaining via `ErrorOptions`, and `name` defaulting to the subclass. `isHarnessError` narrows at seams.
@@ -21,6 +19,6 @@ A single `HarnessError extends Error` base in `dsh-llm` (the leaf package every
 - Errors are machine-routable end-to-end: a plugin can branch on `error.code` rather than substring-matching a message.
 - One base class is imported widely, but it lives in the package everyone already depends on, so the cost is a single import, not a new edge.
 - `deriveMessages` does not surface `error` into model history — the model still sees the text block; the structured field is for code and replay.
- Reverting this PR returns the earlier errors to plain `Error`+`code` form; nothing else in the stack depends on the shared base.
+- Argument validation and dev invariants retain their existing codes and behavior; the shared base adds cross-seam routing metadata without changing model-facing text.

 <!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->
@@ -22,4 +22,4 @@ The rule they enforce: **anything the StreamChunk vocabulary cannot express for

 ## Consequences

-Double the adapter maintenance and double the key-gated e2e surface (both adapters cover V4 Flash and Pro across representative thinking/effort modes). Bought: a continuously-verified neutrality guarantee for the most leak-prone abstraction in the codebase, and a worked second example for adapter authors. The two share the core Config shape (`apiKey`/`baseURL`/`models`) so a deployment swaps mostly one line, but the reasoning knob differs — `dsh-llm-deepseek` takes `thinking`/`reasoningEffort`, `dsh-llm-pi-ai` takes a single `reasoning` level — so a swap translates that field. If the maintenance cost ever outweighs the verification value (e.g. once conformance tests from [architectural conformance](../../proposed/process/2026-06-11-architectural-conformance.md) cover the contract mechanically), retiring the twin to a single adapter + the conformance kit would be a new RFC superseding this one.
+The twin doubles adapter and key-gated e2e maintenance—both cover V4 Flash and Pro across representative reasoning modes—in exchange for continuous seam-neutrality validation and a second implementation example. Both use `apiKey`, `baseURL`, and `models`; the hand-rolled adapter exposes `thinking`/`reasoningEffort`, while pi-ai exposes one `reasoning` level. A future conformance suite could justify retiring one adapter through a superseding RFC.
@@ -2,8 +2,6 @@

 Status: implemented

-> Merges the original proposal and the decision record for one topic. The proposal's full method-surface and write-path detail lives in git history; this records the decision and the durable, contested choices.
-
 ## Problem

 Sessions lived only in memory. The example `session-jsonl.ts` plugin (duplicated byte-for-byte in both examples) was write-only telemetry: it buffered `session/event` and appended JSON lines, with no read/replay path, no crash-safety (no fsync, no atomic write, a fire-and-forget dispose drain), no listing, and no format versioning. Nothing could rehydrate a past session from disk into a live agent, so durable resume ("continue yesterday's task"), durable forking, and the ACP `session/load` method ([ACP support](../../implemented/feature/2026-06-14-acp-agent-client-protocol.md)) were all impossible.
@@ -20,7 +18,7 @@ Persistence is an abstract **capability seam** ([capability seams](2026-06-13-ca
 Key choices recorded here because they are durable, contested, and surprising:

 - **The canonical durable log persists every `SessionEvent` verbatim, including `assistant/chunk`.** `deriveMessages()` skips chunks, and a chunk-filtered rollout (Codex's `policy.rs`) is tempting — but `seq = log.length` and the load-validation `events[i].seq === i` require a *contiguous* log; filtering chunks out would leave holes and break both the contract and resume. A chunk-filtered projection is possible later as a derived view with its own renumbering, but it is NOT the canonical log.
- **Append-only; a crashed turn is closed, never truncated.** Committed events — those at or below a flushed `turn/end` — are never rewritten. The loop only flushes at `turn/end`, so a crash can leave a durable log whose final turn never closed: real, fully-written events sit after the last `turn/end`. **A single turn can be huge in a long-horizon task** (many steps, large tool output spanning a long autonomous run), so discarding the interrupted turn would silently destroy a large amount of real work — truncating a turn is wrong. Instead, on reload `load` PRESERVES those events and CLOSES the orphaned turn by durably appending the minimal synthetic boundary events: an error `tool/result` for every `tool-call` the crash left unanswered, then a `step/end` if a step was still open, then a `turn/end` carrying the merge-extensible `{ kind: 'interrupted' }` reason (a marker that records the turn was cut short by a crash, not completed by the model — no loop ever emits it). The synthetic tool results matter for resume correctness: the loop logs the `assistant/message` (carrying the `tool-call` blocks) BEFORE running the tools, so a crash mid-tool leaves calls without results; `deriveMessages()` would then replay a dangling assistant tool-call, which every provider rejects as an invalid transcript on the next request. Answering each orphaned call with an error result keeps the rehydrated history valid. `load` returns the balanced log, so a resumed session is immediately usable. The ONLY thing discarded is a never-fully-written **torn tail fragment** — a final record whose bytes (JSONL) or row were never completely flushed; that fragment is not a valid event and is dropped before the synthetic closers are written. A parse error or `seq` gap in the COMMITTED region (at or before the last real `turn/end`) is genuine corruption and makes the session unloadable.
+- **Append-only; a crashed turn is closed, never truncated.** Events through a flushed `turn/end` are never rewritten, and the loop flushes only at turn end. Because one interrupted turn may contain substantial valid work, `load` preserves its contiguous, parseable events and appends error results for unanswered tool calls, a missing `step/end`, and `turn/end` with `{ kind: 'interrupted' }`. The synthetic results keep resumed provider transcripts valid. Only an incomplete final record is discarded; a parse error or sequence gap at or before the last real `turn/end` is corruption and makes the session unloadable.
 - **File backend canonical, DB backend a proven drop-in.** `SessionEvent` maps 1:1 onto a row `(session_id, seq, type, time, data)` — `append` is INSERT (in a transaction asserting the contiguous-seq contract), `load` is SELECT … ORDER BY seq. `dsh-session-persistence-sqlite` is exactly this: a `SessionPersistence` subclass with no interface change (opencode runs this exact shape on SQLite/WAL), and it passes the same `runPersistenceContract` suite as the JSONL backend — so the contract holds both backends to identical semantics (lazy materialization, interrupted-turn close on load, contiguous-seq), expressed once over file bytes and once over rows.
 - **Metadata is out-of-log.** Format version, cwd, and lineage are storage concerns, not replayable conversation state, so they live in a `SessionHeader` owned by `dsh-session` and attached to a `Session` via a new readonly `session.header` — never in `SessionEventMap`, never reaching `deriveMessages()`. The alternative (a merge-extensible `session/meta` event as log line 0) was rejected: an in-log event would ride along with a seeded/forked session for free, but metadata is not replayable state, so the explicit out-of-log header seam is the cleaner cost. (The header was originally split into an immutable `SessionHeader` plus a mutable `SessionSummary` whose union was `SessionMeta`; the mutable summary was later removed as dead state — see [Drop the mutable session summary](../simplification/2026-06-19-drop-mutable-session-summary.md).)
 - **`ctx.agents.create()` and `ctx.agents.resume()` are async factories; resume additionally crosses the persistence boundary.** `ctx.agents.resume({ resumeSessionId })` awaits `ctx.sessionPersistence.load`, recreates the live session with the loaded events (so `lastTurnNumber`/`deriveMessages` continue), and starts a fresh agent on the resumed id (NOT `${agentId}-session`). The agent-loop does NOT hard-inject `sessionPersistence` (that would pend non-persistent demos forever); `resume` rejects with a clear error when it is absent.
@@ -33,4 +31,4 @@ Format versioning: the header carries a `version`; `load` rejects any non-curren

 ## Consequences

-Two new packages and the metadata seam in `dsh-session` (`session.header`, the `create(id?, options?)` signature). Bought: durable resume/fork, a read/replay path, crash tolerance, and the foundation the ACP `session/load` ([ACP support](../../implemented/feature/2026-06-14-acp-agent-client-protocol.md)) needs — all over the existing event-sourced log, with the backend swappable behind one interface. The reusable `runPersistenceContract` suite holds every backend to the same append-only / contiguous-seq / lazy-materialization / serializability semantics. This completes [event-sourced sessions](2026-06-11-event-sourced-sessions.md)'s deferred "real persistence backend" and resolves its `TODO(review)` on the event vocabulary: persisting the log freezes its shape, and the `assistant/chunk` fidelity question is answered above (persist verbatim).
+Two new packages and the metadata seam in `dsh-session` (`session.header`, the `create(id?, options?)` signature). Bought: durable resume/fork, a read/replay path, crash tolerance, and the foundation the ACP `session/load` ([ACP support](../../implemented/feature/2026-06-14-acp-agent-client-protocol.md)) needs — all over the existing event-sourced log, with the backend swappable behind one interface. The reusable `runPersistenceContract` suite holds every backend to the same append-only, contiguous-seq, lazy-materialization, and serializability semantics. Persisting the full log also settles event fidelity: `assistant/chunk` remains verbatim.
@@ -37,4 +37,4 @@ Costs: `agent.inject()` while idle now writes three log lines instead of one, an

 The rule is intentionally producer-enforced and dev-checked rather than reader-tolerated: a future backend (SQLite/WAL) inherits the same clean boundary for free, and a plugin that records an event outside a turn fails loudly in dev instead of silently losing data on the next reload.

-The invariant also constrains where the loop may record an `error` event. A failure detected while a turn is open is appended INSIDE the turn (before `turn/end`); but a failure that surfaces once the turn is already closed — a rejecting `session/flush`, which runs as the post-`turn/end` durability checkpoint — has no in-turn position left. Appending an `error` there would land it past the last `turn/end`, exactly the crash-tail position a backend discards. So that post-turn failure is reported via the `agent/error` event and the logger only, never as a `SessionEvent`; the turn stays balanced and persistence keeps its buffered events for the next checkpoint. If durable operational diagnostics are ever needed, they belong on a separate telemetry channel, not the replayable session log.
+Failures detected during a turn are logged before `turn/end`. A later flush failure has no valid in-turn position, so it is reported through `agent/error` and logging rather than appended as a session event. This preserves a balanced replay log; durable operational diagnostics require a separate telemetry channel.
@@ -34,7 +34,7 @@ The first consumer is deliberately text-file-only: `dsh-tool-fs` exposes model-f

 Filesystem permissions and sandboxing are not implied by this split. The local backend resolves relative paths from its configured base directory, but containment policy is a separate decision: either a stricter `ctx.fs` implementation enforces it, or a permission/sandbox plugin wraps `tools/execute` and vetoes calls before they reach the consumer.

-Read-before-write/edit and observed-state are policy, contributed by the `dsh-fs-policy` plugin through the `fs/*` event gate — NOT stored on `ctx.fs`. The provider seam offers an optional version guard on its mutations (`writeText`/`editText` take an optional expectation); the policy plugin decides that guard by listening on `fs/write-intent`/`fs/edit-intent` and records observed versions on `fs/observed`. The executor (`dsh-tool-fs`) passes the current tool execution context as the opaque event actor; the policy plugin derives the observed-state owner from it, normally `exec.agent.session`. `dsh-fs` treats the actor as opaque and never reads it; `dsh-tool-fs` never reaches into the policy plugin. Authorization is version freshness: any read records the file's version, and a later write/edit is authorized as long as the file is unchanged. (This RFC first placed the observed-state store on `ctx.fs`; the split to `dsh-fs-policy` on the `fs/*` event gate is decided by [the split-fs-seam](../simplification/2026-06-26-fsspec-style-fs-seam.md) and [event-gate](2026-06-26-file-context-as-event-gate.md) RFCs.)
+Read-before-write/edit and observed state belong to `dsh-fs-policy`, not `ctx.fs`. Through the `fs/*` event gate, the policy records versions per opaque actor and supplies optional mutation expectations; the provider enforces freshness atomically. `dsh-tool-fs` emits the events without depending on the policy. See the [split-seam](../simplification/2026-06-26-fsspec-style-fs-seam.md) and [event-gate](2026-06-26-file-context-as-event-gate.md) RFCs.

 ## Package topology

@@ -12,30 +12,28 @@ Three seams: the queue-aware cancel, the `AgentHandle` disposer, and the bash ow

 ### 1. Queue-aware `Agent.cancel(reason?)`

-A new `cancel()` verb on the `Agent` interface — the single public stop primitive. (It originally shipped alongside a narrower step-only `abort()`; that verb was later removed as unused, leaving `cancel()` the only public way to stop work.) It clears the inbox's queued + steering FIFOs, aborts the in-flight step if any, and drives a **turn-scoped cancellation marker** the driver loop checks at every turn-decision point — so a prompt that is queued-but-not-yet-started never runs, a cancel landing in the pre-step / continuation window drops the about-to-run turn (ending it `aborted`), and a later prompt cannot be batched into the cancelled turn. `whenIdle()` reaches post-cancel quiescence. ACP `session/cancel` maps to `cancel()`. The marker is armed ONLY when there is something to cancel, so an idle no-op cancel cannot strand the next prompt.
+`cancel()` is the single public stop primitive. It clears queued and steering input, aborts an in-flight step, and arms a turn-scoped marker checked at each turn boundary. A queued prompt therefore cannot start after cancellation or absorb later input. `whenIdle()` waits for post-cancel quiescence, and ACP `session/cancel` maps to this method. An idle cancel does not arm the marker.

 ### 2. `AgentHandle` async disposer

-`ctx.agents.create`/`resume` (and the `AgentFactory` interface) return `AgentHandle = { agent: Agent; dispose(): Promise<void> }`. The disposer is a **consumer capability** — a registry observer holding only the bare `Agent` cannot tear it down. The caller fiber and registered factory provider are structural co-owners: caller unload enforces structured ownership, while provider unload must stop old instances whose scoped dependency surface resolves through that provider. All three paths reach the same memoized teardown: stop the loop, await its exit and idle flushes (true quiescence, not just the `disposed` status flip), detach the agent, detach its session, and unwind its scope. Each public ID becomes reusable when its exact registry entry detaches; there is no separate reservation-release phase. Config-created agents are already owned by the `AgentLoop` fiber (the handle is discarded). ACP holds each session's disposer in its `SessionRecord` and runs it on disconnect/teardown, so a bare client disconnect leaves no registered agent and no session-store entry — even when `session/load` races teardown (the just-resumed handle is disposed before the closed-guard throw).
+`ctx.agents.create`/`resume` and `AgentFactory` return `AgentHandle = { agent, dispose() }`. Disposal is a consumer capability; an observer holding only `Agent` cannot tear it down. The caller fiber and factory provider also own the instance, and every path shares one memoized teardown: stop the loop, await quiescence and flushes, detach the agent and session, then unwind its scope. IDs become reusable when their registry entries detach. Config-created agents belong to the loop fiber; ACP stores and disposes each session handle.

-**Teardown ORDER is load-bearing for durability**, and the implementation folds the session lifecycle into the agent's SINGLE composite cordis effect (`SessionStore.prepare`/`enter`/`announce`, replacing a sibling-effect split). A fiber unload disposes sibling effects concurrently (`Promise.all`), which would race removing the session store's append publication hooks against the loop's closing `session/flush` and drop the closing `turn/end`; inside one effect the disposers run as an ordered LIFO chain (loop stopped + `await agent.done` BEFORE the session detaches), so the loop's final flush is captured on BOTH the handle's `dispose()` and a fiber unload. The contained `agent/disposed` and `session/disposed` notifications cannot reject the chain or skip later teardown.
+Teardown order is load-bearing for durability. The session lifecycle and loop share one composite Cordis effect so LIFO disposal stops the loop and awaits `agent.done` before detaching the session. Sibling effects would dispose concurrently and could remove append hooks before the closing flush. Disposal notifications are contained so they cannot interrupt the chain.

 ### 3. Bash owner token in the seam

-Background-task ownership moved from a `tool-bash` plugin-local `Map<string, Agent>` into the executor. `BashExecRequest` gains an optional `owner?: string`; the resolved `BashExecSpec` carries it as required-but-nullable `owner: string | undefined` (a forgotten owner is a visible `undefined`, never a silently-absent property). The executor stores the token on its task and exposes it via a new `BashExecutor.ownerOf(id): string | undefined` seam (NOT on the public `BashTask` — one read path, no redundant API). `tool-bash` deletes its `Map` entirely: it stamps `exec.agent?.session.header.id` as the owner at `start`, and `bash_output`/`bash_kill` compare `ctx.bash.ownerOf(id)` to the caller's token with `!== undefined` semantics (an empty-string token is still a real owner). The completion notice finds the live agent by scanning `ctx.get('agents')?.list()` for `agent.session.header.id === ownerToken` (read via `ctx.get` — `onTaskDone` runs on the bash fiber, a foreign fiber, where the `ctx.agents` proxy would throw). Because ownership now lives on the task in the executor (disposed with the `dsh-bash` fiber), it SURVIVES a `tool-bash` HMR reload — closing the old `XXX(tool-bash-owner-hmr)` gap. (The `onTaskDone` listener is still effect-scoped to `tool-bash`'s `apply`, so a completion landing during the reload gap still drops its one notice — the pre-existing reload-gap drop — but the ownership fence itself is HMR-proof.)
+Background task ownership belongs to the executor. `BashExecSpec.owner` carries an optional opaque token, `ownerOf(id)` reads it, and `dsh-tool-bash` stamps the calling session token at start. `bash_output` and `bash_kill` reject mismatched callers; completion notices locate the live agent by session token through the registry. Keeping ownership on the task preserves the fence across tool-plugin reloads. The completion listener remains effect-scoped, so a notice that settles during the reload gap may still be dropped.

 ## Verification

-These invariants hold and are pinned by tests:
-
- ACP disconnect/session close leaves no registered agent AND no session-store entry for that session, even when `session/load` races teardown.
- `session/cancel` before a queued prompt starts prevents that prompt from running and cannot batch the next prompt into the cancelled turn.
- A `tool-bash` HMR reload does NOT make an existing background task readable or killable by a different session (ownership survives on the executor).
- Existing non-ACP demos still work without managing handles explicitly; config-created agents remain owned by the `AgentLoop` plugin fiber.
+- ACP disconnect or session close leaves no registered agent or session-store entry, including when `session/load` races teardown.
+- Cancelling before a queued prompt starts prevents that prompt from running or absorbing the next prompt.
+- Reloading `dsh-tool-bash` does not let another session read or kill an existing background task because ownership remains on the executor.
+- Config-created agents remain loop-fiber-owned, so non-ACP demos need not manage handles explicitly.

 ## Session owner tokens are unique among live agents

-The bash owner-token comparison relies on `session.header.id` being unique among live agents. Concurrent same-ID operations may both prepare privately, but publication enters the session and agent in order; `SessionStore.enter()` rejects a duplicate live session id, and every losing transaction rolls its private state back. A programmatic caller therefore cannot publish two live agents with one session token. The access *policy* (token comparison) stays in `tool-bash` (the consumer); the bash seam stores only an opaque `owner` string and never interprets it — the correct interface/implementation/consumer split.
+The bash owner token relies on `session.header.id` being unique among live agents. Concurrent same-ID operations may prepare privately, but `SessionStore.enter()` rejects duplicate publication and the losing transaction rolls back. `tool-bash` owns the comparison policy; the bash seam stores an opaque `owner` string without interpreting it.

 ## Alternatives considered

@@ -4,7 +4,7 @@ Status: implemented

 ## Problem

-The `Session` event log is the single source of truth ([event-sourced sessions](2026-06-11-event-sourced-sessions.md)), but the only view over it was `deriveMessages()` — a linear scan that filtered and transformed raw events into `Message[]`. This creates problems for session-history-manipulating plugins (compaction, tool-call result pruning, etc.). Without a central mechanism, each plugin would need to wrap `agent/request` to rewrite the message list — a pattern that suffers from listener-ordering fragility, provides no durable record of what was changed, and forces repeated changes to the core `deriveMessages()` whenever a new manipulation is added. A central hub in the `session` package, with a provenance-recording mechanism and enough flexibility for future plugins to manipulate session history through a stable API, lays a solid foundation for plugin development.
+The event log is authoritative, but history manipulation had no durable shared mechanism. Plugins such as compaction would otherwise rewrite derived requests through order-sensitive listeners, leave no provenance, and require repeated changes to `deriveMessages()`.

 ## Decision

@@ -49,7 +49,7 @@ The `repair.ts` module synthesizes `tool/result` closers for orphaned tool calls

 The dev-mode invariants plugin validates: `sourceEventSeqs` references (non-empty, no duplicates, references earlier events, references known seqs) and `surfaceOp` (replace `start ≤ end`, both endpoints are on the tracked surface, the range is non-reversed in surface position, and `sourceEventSeqs` includes every node the range shadows).

-Because the surface is the SOLE derivation path, a surface-eligible event that carries no `surfaceOp` marker is invisible to `deriveMessages()` — it would land in the log yet silently drop from history on resume/fork. `append`'s typed overload makes the marker mandatory for `SurfaceEventType` events at compile time, but only when the type argument is a SPECIFIC literal; when it widens to the `SessionEventType` union (a caller iterating raw events, e.g. `for (const e of log) append(e.type, e.data)`) the conditional rest collapses to optional and the compiler stops enforcing it. The marker requirement is therefore ALSO checked at runtime in two places: `append` itself throws on a marker-less surface-eligible event (covering the union-widening loophole), and the `Session` seed constructor re-checks the same invariant (alongside its seq-contiguity and JSON-serializability checks) so a seed/load/fork — which arrives as raw `SessionEvent[]`, bypassing `append` — is REJECTED rather than constructing a session that resumes with missing history. (No backward-compat path for surface-less logs: per the pre-release stance there is no persisted user data to preserve, so such a log is rejected, not upgraded.)
+Every surface-eligible event must carry `surfaceOp` or it would disappear from derived history. Typed `append` overloads enforce this for literal event types; runtime checks in `append` and the seed constructor cover widened unions and loaded logs. Invalid seeds are rejected rather than upgraded under the pre-release format policy.

 ## Alternatives considered

@@ -39,4 +39,4 @@ The shared `runPersistenceContract` (public-API contract) keeps running for ever

 ## Consequences

-The pre-extraction duplication was verbose but explicit — each backend read top-to-bottom. The coordinator adds one indirection (the hook seam) and one new concept (the opaque torn marker). This clears the bar because the centralized logic is the correctness-heavy part that was already being fixed twice, and the hook set is narrow (six methods, no inheritance). The hook surface was deliberately held to the minimum: the create-collision probe is NOT a separate hook — it folds into `loadStored(id) !== undefined`; there is no separate `materialize` hook (folded into `appendBatch` for atomicity); `list()` stays a backend method with no coordinator pass-through (listing needs none of the orchestration). The net effect is a reduction: one orchestration copy instead of two, the backends shrank by ~1200 lines of duplicated churn, and a future backend implements a handful of small primitives instead of copying the entire `session/event` → buffer → flush machinery.
+The coordinator adds one indirection and an opaque torn marker, but centralizes correctness-heavy orchestration previously duplicated by every backend. Its hook surface stays narrow: collision checks reuse `loadStored`, materialization stays atomic inside `appendBatch`, and listing bypasses the coordinator. New backends implement storage primitives rather than copy the event-buffer-flush lifecycle.
@@ -6,11 +6,11 @@ Status: implemented

 The harness already brands three identifiers — `CallId` (`packages/llm/llm/src/brand.ts`), `SessionId` (`packages/core/session/src/types.ts`), and `AgentId` (`packages/core/agent/src/types.ts`) — using the `Branded<B> = string & { readonly [BRAND]: B }` machinery (owned by the type-only `@deepseek-ai/dsh-brand` package at `packages/util/brand/` — see its [README](../../../../packages/util/brand/README.md)) and a zero-cost cast factory per type. `dsh-brand` also states the governing policy: *"Branding is for ids that cross package boundaries and could plausibly be confused; not every string needs a brand."* That policy is right; the problem is that it is only half-applied. Two gaps let a structurally-identical-but-semantically-wrong string slip through the type checker today.

-**Gap 1 — unbranded cross-boundary IDs in the bash seam.** The background-task id is a plain `string`: `BashTask.id: string` (`packages/bash/bash/src/types.ts`), carried as `string` through the whole executor seam (`BashExecutor.get`/`ownerOf`/`readOutput`/`kill(id: string)` in `packages/bash/bash/src/index.ts`) and validated/passed as `string` by the model-facing tools (`validateTaskId`, `assertTaskAccess`, the `task_id` schema arg in `packages/bash/tool-bash/src/index.ts`). It is generated by a per-executor counter — `` `bash-${this.nextTaskId++}` `` in `packages/bash/bash-local/src/index.ts` — which gives it **exactly the same `name-N` shape as `SessionId`'s default** (`` `session-${++counter}` `` in `packages/core/session/src/index.ts`). A bash task id and a session id are trivially swappable at a call site and the compiler says nothing. This is the headline case the user asked about, and it is a model-facing id (the model passes `task_id` back to `bash_output`/`bash_kill`), so a confusion here is reachable from untrusted input.
+**Gap 1 — unbranded IDs in the bash seam.** `BashTask.id` and every executor/tool boundary used bare `string`, even though the generated value has the same `name-N` shape as default session ids. The model also returns this value through `task_id`, so confusing task and session ids was both type-correct and reachable.

 The bash **owner token** is the related sub-case: `BashExecRequest.owner?: string` and `BashExecSpec.owner: string | undefined` (`packages/bash/bash/src/types.ts`) are documented as a deliberately *opaque* isolation key, but in every live caller the value IS the owning agent's `session.header.id` (`callerToken = (exec) => exec.agent?.session.header.id` in `packages/bash/tool-bash/src/index.ts`) — i.e. a `SessionId` wearing a `string` disguise. It is compared for access control (`owner !== callerToken(exec)`), so a mismatched-but-well-typed string here is a cross-session isolation bug the type system currently cannot catch. This is the same `session.header.id`-as-owner alias that the [unify-the-agent-id-and-the-session-id](../../proposed/simplification/2026-06-20-unify-agent-and-session-id.md) proposal calls the "bash owner-token alias hole".

-**Gap 2 — brand erosion at the seams of the *already-branded* IDs.** Even `CallId`/`SessionId`/`AgentId` decay back to bare `string` at exactly the places confusion is most likely: the registry/store `Map` key types and most public method params. Representative sites: `SessionStore.store = new Map<string, Session>()` and `create`/`prepare(id?: string)`/`get(id: string)` (`packages/core/session/src/index.ts`); `AgentRegistry.store = new Map<string, Agent>()` and `register`/`get(id: string)` (`packages/core/agent/src/index.ts`); `ToolPresenter.pending = new Map<string, …>()` keyed by call id and `call(callId: string)`/`result(callId: string)` (`packages/ui/acp/src/index.ts`); the ACP session-id surface beyond the store map — `SessionRecord.sessionId: string`, `bySession = new WeakMap<Agent, string>()`, `loadingIds = new Set<string>()`, `requireSession(sessionId: string)`, and the exported `streamSessionEventUpdate(sessionId: string, …)` (`packages/ui/acp/src/index.ts`); and the persistence coordinator's `Map<string, …>` keyed by session id (`packages/session-persistence/session-persistence/src/coordinator.ts`). A brand that is dropped at the `Map` key buys nothing on lookups — the value of the existing brands is partly unrealized.
+**Gap 2 — erosion of existing brands.** `CallId`, `SessionId`, and `AgentId` became bare strings in registry maps, public lookup parameters, ACP session tracking, and the persistence coordinator. Dropping a brand at a lookup boundary defeats its main protection.

 ## Decision

@@ -44,7 +44,7 @@ export function OwnerToken(id: string): OwnerToken {

 ### Why not typing `owner` as `SessionId`?

-The obvious shortcut is to type `owner` as `SessionId` directly — it always *is* one. We reject that. The bash executor seam is a capability seam (interface `dsh-bash`, implementation `dsh-bash-local`, consumer `dsh-tool-bash`) and its owner token is *documented as deliberately opaque*: the executor "never interprets it (no access policy lives in the seam — that is the consumer's job)" (`packages/bash/bash/src/types.ts`). Typing the seam's field as `SessionId` would import `dsh-session`'s vocabulary into a package that must not know what an owner token *means* — it would couple a generic execution backend to the session model and contradict the opaque-token design. A sandboxed or remote executor that replaces `dsh-bash-local` should not inherit a session dependency. The distinct `OwnerToken` brand keeps the seam decoupled: `dsh-bash` knows only "an owner is some opaque branded token," and the `dsh-tool-bash` consumer — which already decides the access policy — is the single boundary that casts its `SessionId` into an `OwnerToken`. The brand still delivers the safety win (you cannot pass a `BashTaskId` or a raw string where an owner is expected) without the coupling.
+The executor treats ownership as opaque and must not depend on the session model. A distinct `OwnerToken` preserves that boundary while preventing raw strings or task ids from being passed as owners. `dsh-tool-bash`, which owns the access policy, performs the single conversion from `SessionId`.

 ## Out of scope / possible extensions

@@ -58,7 +58,7 @@ Kept deliberately narrow per the "not every string needs a brand" policy. Each o

 ## Verification

-The landed invariants: `BashTaskId` and `OwnerToken` are defined in `dsh-bash` and threaded end-to-end (executor seam, the `dsh-bash-local` generation site, the `dsh-tool-bash` model-facing surface) with no `dsh-bash` dependency on `dsh-session`; no collection keyed by an in-scope branded id (`CallId`/`SessionId`/`AgentId`/`BashTaskId`) is keyed by bare `string` — `Map` keys, `WeakMap` value slots, `Set` membership (the ACP `bySession`/`loadingIds`), public method params, and exported signatures (`streamSessionEventUpdate`) all take the brand; and brands are constructed via the cast factory at each boundary where a raw string enters (provider call id, ACP session id, model-supplied `task_id`), never as scattered `as` casts.
+`BashTaskId` and `OwnerToken` are defined in `dsh-bash` and threaded through the executor, local implementation, and model-facing tool without adding a `dsh-session` dependency. Collections, public parameters, and exported signatures use the applicable brand for `CallId`, `SessionId`, `AgentId`, or `BashTaskId` rather than bare `string`; raw provider, ACP, and model inputs enter through the brand factory instead of scattered casts.

 ## Consequences

@@ -6,14 +6,14 @@ Status: implemented

 An example folder is supposed to be *thin* — the variable wiring of a demo, not the demo's machinery. Before this change it was thick. Each example carried a hand-rolled `start.ts` boot bootstrap, an infra preamble (`timer`, and — for the stdio demos — `logger` + `hmr`), nested includes of three shared YAML fragments (`base.yml` / `base-core.yml` / `acp-agent/acp-tail.yml`), and per-example `agent-loop`/persistence/system-prompt config. The actual app — the spine of services every agent needs — was spread across the leaf and those includes.

-The deeper problem was a **coupled front-door cluster** that lived at the leaf with nothing enforcing it. Choosing the ACP bridge over `ui-stdio` was not one swappable line: an ACP server must **drop the stdout console logger** (stdout is the JSON-RPC channel — a stray log corrupts the frames) and pre-create **no** agents (ACP `session/new` creates them on demand), whereas the stdio app needs a console logger and a pre-created `main`. (`timer` is the one infra plugin common to both — it writes nothing to stdout — so it belongs in the shared spine, not the cluster.) That coupling was enforced only by prose warnings in the leaf YAML. A leaf that wired a console logger into the ACP config was a one-line, comment-only mistake away — exactly the [stdout-purity footgun](../feature/2026-06-18-acp-terminal-and-tool-rendering.md) the examples guarded by hand. The three `start.ts` files also duplicated the Loader-boot tail, the `.env` loader, and (for ACP) snapshot-mode branching and the stdin-dispose lifecycle.
+The leaf configs also owned a coupled front door. ACP requires stdout purity and creates agents through `session/new`; stdio requires a console logger and a pre-created `main`. Prose warnings were the only guard against combining these incorrectly, while three `start.ts` files duplicated the Loader bootstrap and lifecycle code.

 ## Decision

 Each example is now **mostly an invocation of an app package**, splitting the wiring along the existing [interface / implementation / consumer seam](2026-06-13-capability-seams.md): the **app package owns the composition**, the leaf `cordis.yml` owns only the **swappable choices** (which LLM adapter, which bash executor, model, prompt, persistence root).

- **`@deepseek-ai/dsh-agent-core`** ([packages/core/agent-core](../../../../packages/core/agent-core)) — a Cordis bundle plugin for the providerless, executor-less, UI-less spine: `timer` + `llm` + sessions + system-prompt + tools + agents + invariants + `tool-bash` + `agent-loop`, mounted as child plugins inside its `apply(ctx)` via `ctx.plugin(...)`. This is the old `base-core.yml` **minus** `bash-local`, **plus** `timer` and the loop, as code instead of a YAML include. The bundle **forwards** `agent-loop`'s `agents` list as its own config (`export const Config = AgentLoop.Config`, default `[]`, the existing `AgentLoop.Config` shape in [packages/core/agent-loop/src/index.ts](../../../../packages/core/agent-loop/src/index.ts)) — so each app supplies its own pre-created agents. This is precisely the reason the old `base-core.yml` gave for keeping `agent-loop` *out* of the shared core ("the examples disagree — stdio needs a pre-created `main`, acp needs none"); forwarding the config dissolves that objection — the loop is shared, the agents list is per-app. The bundle children register into the root service store, so a leaf-mounted sibling (the adapter, the executor) sees them exactly as a nested `plugin-include` subtree's services were seen before. Depending on the CONCRETE `dsh-agent-loop` (not just the `dsh-agent` interface) is deliberate and is the sanctioned exception to the "extension plugins depend on interfaces, never on the concrete loop" rule (packages/README.md, docs/architecture.md § Service map): the rule constrains plugins that EXTEND the system, whereas this bundle's whole job is to COMPOSE the concrete spine. Swapping the loop means publishing a different bundle, not rewiring every extension.
- **`@deepseek-ai/dsh-stdio-agent`** ([packages/ui/stdio-agent](../../../../packages/ui/stdio-agent)) and **`@deepseek-ai/dsh-acp-agent`** ([packages/ui/acp-agent](../../../../packages/ui/acp-agent)) — app packages, each consuming `dsh-agent-core` and **baking in its coupled front-door cluster**: stdio = `ui-stdio` + console logger + a pre-created `main`; acp = the `acp` bridge + JSONL persistence + **no stdout logger** + no pre-created agents. The leaf no longer carries the cluster, so it has no logger entry to copy wrong by default — the common stdout-purity mistake loses its foothold. (A leaf can still *add* a sibling logger entry — a package cannot forbid what a leaf author writes — so the rule "never add a stdout logger to an ACP leaf" stays documented at the leaf; what changed is that the default leaf has nothing to get wrong.) They land under the existing `ui` group alongside `acp`, so no new package group (and no `tsconfig`/`packages/README` group plumbing) was needed.
+- **`@deepseek-ai/dsh-agent-core`** ([packages/core/agent-core](../../../../packages/core/agent-core)) composes the providerless, executor-less, UI-less spine and forwards the loop's agent-list config. Its dependency on the concrete loop is intentional because this package composes the spine rather than extending it; swapping the loop means supplying another bundle.
+- **`@deepseek-ai/dsh-stdio-agent`** ([packages/ui/stdio-agent](../../../../packages/ui/stdio-agent)) and **`@deepseek-ai/dsh-acp-agent`** ([packages/ui/acp-agent](../../../../packages/ui/acp-agent)) bake in their front doors. Stdio includes `ui-stdio`, a console logger, and `main`; ACP includes the bridge and JSONL persistence but no stdout logger or pre-created agent. Leaves may add plugins, but the safe composition is now the default artifact.
 - **`start.ts` is gone.** Each app package exposes a `bin` (`dsh-stdio-agent` / `dsh-acp-agent`); the `demo:*` scripts invoke it (e.g. `dsh-stdio-agent ./cordis.yml`). The Loader-boot tail, `.env` loading, and fail-loud guards live in the shared [`@deepseek-ai/dsh-app-boot`](../../../../packages/ui/app-boot) package (unit-tested under the per-file coverage gate — see [share the app bins' boot glue](../simplification/2026-07-04-share-app-bin-boot-glue.md)); each bin is a thin self-executing composition over those helpers plus its app-specific lifecycle (the ACP bin: snapshot-mode selection and stdin-dispose). The `bin.ts` files themselves stay coverage-excluded (self-executing CLI entries, like the old `start.ts`) and are driven by the keyless Loader-path tests.
 - **Each leaf `cordis.yml` collapses** to backends + config: the LLM adapter (`llm-deepseek` with apiKey/models, or `llm-replay`), the bash executor (`bash-local`), `hmr` for the stdio demos (see the amendment below), and one app entry carrying the app's config (model, system prompt, persistence root — surfaced as the app package's own `Config`, which routes each value to wherever the app wires it: stdio onto its pre-created agent, acp onto the bridge plugin).
 - **echo-agent folds onto `dsh-stdio-agent`**, swapping the LLM backend to the local `mock-llm` and adding the local `echo-tool` (plus `bash-local`, which the spine's `tool-bash` injects) at the leaf — the clean demonstration of "swap the backend, keep the app". `mock-llm.ts` / `echo-tool.ts` stay as example-local teaching plugins.
@@ -38,10 +38,10 @@ The old `base*.yml`/`acp-tail.yml` includes already deduped the *config*, but a

 ## Verification

- Each example directory is `cordis.yml` (+ the acp `cordis.snapshot.yml`) + `README.md` + tests only — no `start.ts`, no infra preamble; `base.yml`/`base-core.yml`/`acp-tail.yml` are gone.
- `demo:echo` / `demo:repl` / `demo:acp` run via the app-package `bin`s.
- The new packages carry the per-file 100% coverage gate and a README like every `@deepseek-ai/dsh-*`. Each app package has a keyless **real-load-path** smoke that boots it through its `bin` + the cordis Loader (not a hand-built `ctx.plugin({...})` mount), guarding the `unwrapExports` export-shape bug class ([postmortem 0001](../../../postmortem/0001-acp-default-export-drops-inject.md)).
- The ACP snapshot **replay** transcript is unchanged: the boot restructuring preserved the plugin set + load order, so `pnpm run test:snapshot` stays green against the committed goldens with no re-record.
+- Example directories contain only their config, README, and tests: `start.ts`, the infrastructure preamble, and the shared YAML includes are gone.
+- `demo:echo`, `demo:repl`, and `demo:acp` invoke the app-package bins.
+- Each new package has a README and per-file 100% coverage; each app package also has a keyless real-Loader-path bin smoke that catches export-shape failures described in [postmortem 0001](../../../postmortem/0001-acp-default-export-drops-inject.md).
+- The ACP replay transcript remains unchanged because the plugin set and load order did not change.

 ## Consequences

@@ -12,7 +12,7 @@ The immediate prompt came from OpenRouter's [App Attribution](https://openrouter

 - **OpenRouter's mechanism is provider-specific.** Their current docs say app attribution is tracked through `HTTP-Referer` (required), `X-OpenRouter-Title`, and `X-OpenRouter-Categories`; `X-Title` is only accepted for backward compatibility. Their API reference calls the headers optional and says they make the app discoverable on OpenRouter. This is a concrete OpenRouter contract, not an IETF or OpenAI-compatible API standard.
 - **In agent tooling, `HTTP-Referer` is an OpenRouter-aware convention, not a general agent convention.** It is common enough that OpenRouter SDKs and OpenRouter examples expose it directly, and frameworks that target OpenRouter usually need a way to pass it through. But agent protocols such as ACP negotiate names, versions, and capabilities in their own initialize messages, while model-provider requests still need HTTP-level identity. "Accepted in the agent world" therefore means "recognized by OpenRouter integrations," not "portable across agent runtimes or providers."
- **Observed coding agents use product/version `User-Agent` strings, sometimes with environment context.** A non-exhaustive public-code survey found OpenAI Codex building `{originator}/{version} ({os} {os_version}; {arch}) ...` and carrying an `originator` header; Google Gemini CLI sending `GeminiCLI[-clientName]/{version}/{model} ({platform}; {arch}; {surface})` or a Cloud Code VS Code variant; Cline's Codex backend client sending `cline/{version} ({platform} {release}; {arch}) node/{nodeVersion}` plus `originator: cline`; SWE-agent setting `swe-agent/{version}` unless the user already supplied a header; Continue setting `Continue/{version}` for its ClawRouter provider plus `X-Continue-Provider`. Aider also appends `Aider/{version} +{website}` to browser-like user agents for web scraping, but that is not a model-provider request path. The pattern is not one exact format; it is product identity in `User-Agent`, with provider-specific side headers only where a provider/backend asks for them.
+- **Coding agents identify the product and version in `User-Agent`.** Public implementations vary in environment detail and provider-specific side headers, but product identity is the common contract; there is no universal exact format.
 - **The standards-track general client identity header is `User-Agent`.** RFC 9110 section 10.1.5 defines `User-Agent` as the user-agent software identity, says it is used for interoperability reports and analytics, and says a user agent SHOULD send it on each request unless configured not to. This is the only standard header that directly matches "what product is making this HTTP request."
 - **`Referer` is standard, but OpenRouter's `HTTP-Referer` is not the standard field.** RFC 9110 section 10.1.3 defines `Referer` as the URI from which the target URI was obtained and spends significant text on privacy restrictions. OpenRouter instead asks for `HTTP-Referer`, using it as an app URL identifier. That name and meaning are OpenRouter-specific even though it resembles the CGI environment variable form of the standard `Referer` header.
 - **`From` is standard but not suitable as a mandatory default.** RFC 9110 section 10.1.2 defines `From` as an email address for the human responsible for a user agent. Robotic agents SHOULD send it so servers can contact an operator, but non-robotic agents should not send it without explicit user configuration because of privacy and security policy concerns. The harness can support an operator contact later, but must not invent one or require it globally.
@@ -22,7 +22,7 @@ Web access is a first-class capability seam following [the capability-seam RFC](

 Providers do not register tools. Providers register capabilities. `dsh-tool-web` is the only owner of model-facing names, descriptions, prompt guidance, JSON schemas, and presentation.

-Search and fetch are separate capabilities and separate model-facing tools, but they are deliberately one seam. `ctx.web` is a single web-access middle layer between provider packages on one side and the tool consumer on the other: one service to inject, one provider-selection policy owner, one abort/error vocabulary, one place a product configures "how this harness reaches the web." The two halves do not share a request schema and have no shared business logic — search normalizes provider-backed discovery into a portable result with optional answer text and citeable sources, while fetch retrieves a concrete public HTTP(S) URL and returns a status code plus bounded decoded content — but they are parallel registries on one capability surface, not two surfaces. The cost is a `WebService` whose registry/exec methods come in `Search`/`Fetch` pairs; that parallelism is intentional, not a missed extraction. Splitting into `dsh-search` and `dsh-fetch` is the rejected alternative below.
+Search and fetch are separate tools but one web-access seam. `ctx.web` owns provider selection, abort/error vocabulary, and deployment configuration for both parallel registries. Their request schemas and provider logic remain separate; the shared service is the product boundary for reaching the web.

 `dsh-tool-web` registers model-facing web tools when the product has enabled those tools and the `ctx.web` seam is present. Backend availability is an execution-time concern, not a schema-registration concern:

@@ -66,7 +66,7 @@ flowchart LR

 `@deepseek-ai/dsh-web` depends only on Cordis and low-level harness support. It declares `ctx.web`, provider interfaces, request/result types, the provider status type, and error codes. It does not import tool, agent, session, LLM, or provider packages.

-Provider packages depend on `@deepseek-ai/dsh-web` and Cordis. They own credentials, endpoint config, provider-specific request mapping, provider-specific response parsing, and provider-specific error translation into `WebError`. They issue network requests with platform-native `fetch` at the repo's Node floor, mirroring `@deepseek-ai/dsh-llm-deepseek`'s adapter, NOT a cordis HTTP-client service (`ctx.http`/`@cordisjs/plugin-http`) — even where a Perplexity provider's request is shaped like an OpenAI-compatible chat completion, that wire shape is a provider-private detail and does not make the provider depend on `ctx.llm`. A provider does NOT own the `ctx.web` key (two search providers cannot both own it): like `dsh-llm-deepseek`, each provider package is a function/namespace plugin (`inject: ['web']`) whose `apply` constructs the backend and calls `ctx.web.registerSearchProvider` / `registerFetchProvider`. `@deepseek-ai/dsh-web` is the `export default` service that owns the key.
+Provider packages depend only on `dsh-web` and Cordis. They own credentials, endpoints, wire mapping, parsing, and `WebError` translation, using platform `fetch`. Each provider injects the shared service and registers a backend; only `dsh-web` owns the `ctx.web` key. Provider-private protocol shapes do not create dependencies on `ctx.llm` or a Cordis HTTP service.

 `@deepseek-ai/dsh-tool-web` depends on `@deepseek-ai/dsh-web`, `@deepseek-ai/dsh-tools`, `@deepseek-ai/dsh-system-prompt`, and Cordis. It never imports concrete provider packages.

@@ -239,7 +239,7 @@ type WebFetchBody =

 `WebFetchResult.url` is the final URL after allowed redirects. The request URL is already present in `WebFetchRequest`, so there is no separate `requestedUrl`/`finalUrl` pair.

-`WebFetchBody` is a CLOSED discriminated union owned by `dsh-web`, not a merge-extensible map. The merge-extensible pattern (`ContentBlockMap`) exists for variants that independent plugins introduce and the seam cannot foresee; body kinds are not that — `dsh-web` declares the kind, the fetch provider decodes it, and `dsh-tool-web` renders it, so a new kind is a coordinated change across three known packages, not a plugin extension. Keeping it closed buys compile-time exhaustiveness: consumers `switch` on `kind` ending in `default: assertNever(body, …)`, so adding a kind breaks compilation at every consumer that must render it (e.g. `tool-web`'s `html`→markdown vs `text` passthrough) until that arm is written. Each arm stays its own object literal even when the fields coincide today, leaving room for arm-specific fields (a future `pdf` body's `pageCount`, a `json` body's parsed value) without reshaping the type. Since the harness is unreleased, extending this closed union later is free (no migration, no compat shim).
+`WebFetchBody` is a closed discriminated union because body kinds require coordinated changes to the seam, provider, and tool rather than independent plugin extension. Exhaustive switches make a new kind fail compilation at every renderer until handled. Separate object arms leave room for kind-specific fields.

 The provider owns safe resource retrieval: URL validation, HTTP transport, redirect policy, timeout, abort propagation, byte caps, charset decoding, content-type classification, and binary rejection. `dsh-tool-web` owns presentation: HTML-to-markdown, HTML-to-text, truncation formatting for the model, and future summaries.

@@ -29,7 +29,7 @@ provider seam dsh-fs            ctx.fs: text IO + ATOMIC mutation primitives who
 provider      dsh-fs-local      local implementation of ctx.fs
 ```

-The model is **additive, not subtractive**: `ctx.fs` on its own is a complete, unconstrained text-storage seam — `read` reads, `write` unconditionally creates-or-overwrites, `edit` unconditionally replaces literal text in the current content. There is no "先读后写", no version check, nothing to remove; the bare provider just does the I/O atomically. `dsh-fs-policy` is a plugin that *adds* constraints on top: observed-state, read-before-edit, and "write/edit must be based on the version you read". So removing `dsh-fs-policy` does not break `dsh-tool-fs` at the service-injection boundary; it removes the policy gate and leaves the bare provider behavior. The intended deployment stance is that a config loading the fs tools also loads `dsh-fs-policy`, so the user-facing behavior and prompt discipline are read-before-write/edit (the `coding-agent` and `acp-agent` demos wire the full stack). The bare-provider mode exists because the tool should not be method-coupled to the policy plugin, not because an unconstrained filesystem is the normal product stance.
+The model is additive: bare `ctx.fs` performs atomic, unconstrained text I/O, while `dsh-fs-policy` adds observed state, read-before-edit, and version guards. Removing the policy therefore leaves the tools usable but unconstrained. Shipped agent configs load the policy; the bare mode exists to keep policy optional at the service boundary, not as the normal deployment stance.

 `dsh-tool-fs` no longer injects `fileContext`. It injects `fs` and `tools`/`systemPrompt`.

@@ -68,9 +68,7 @@ The events live in `@deepseek-ai/dsh-fs`, not in `dsh-fs-policy`. This is forced

 These events carry existing `dsh-fs` vocabulary (`FsTarget`, `FsVersion`, `FsWriteIntent`) plus an opaque actor — not model-facing concepts (no line windows, numbered lines, or rendered footers leak down).

-**The two `fs/*` decision events are single-slot decision points, NOT a composable interception chain.** A waterfall listener that does not call `next()` short-circuits the rest of the chain (verified in [vendor/cordis/src/events.ts](../../../../vendor/cordis/src/events.ts) — `waterfall` runs listeners around the final `next` thunk, and a listener that returns without calling `next()` reaches neither later listeners nor the tool's default thunk). `dsh-fs-policy` fully decides the write/edit expectation and does not call `next()`, so it occupies that one decision slot in the default deployment. This is deliberate: "what version basis does this mutation guard against" is a single decision, not an accumulation. The names (`fs/write-intent`, `fs/edit-intent`) say "produce the value", not "authorize", so they do not imply a stackable authorization chain. Genuinely composable interception (permission, audit, sandbox) belongs on the existing `tools/execute` waterfall, which every tool call already flows through — not on this fs version-decision slot.
-
-**The occupant is decided by registration order — first-registered (or `prepend`ed) wins.** cordis dispatches waterfall listeners in registration order (`push`, or `unshift` for `prepend` — [vendor/cordis/src/events.ts](../../../../vendor/cordis/src/events.ts)), and the first non-`next()` decider short-circuits the rest. So the slot is **first-wins**, and `dsh-fs-policy` owning it rests on the default deployment convention: it is the decider registered for these events. The event shape does NOT itself guarantee "an unread edit is rejected" — a plugin that registers a looser `fs/edit-intent` decider BEFORE `dsh-fs-policy` (or with `prepend`) would decide first and bypass the `FS_NOT_OBSERVED` gate. That is the inherent property of a first-wins single slot, stated here so it is not mistaken for an enforced invariant. This RFC does not add a multi-policy composition mechanism; the implementation requirement is that `dsh-tool-fs` dispatches these waterfalls on every write/edit path and that a config wiring the fs tools loads `dsh-fs-policy` as the policy decider.
+**The two `fs/*` decision events are single-slot, first-wins waterfalls.** `dsh-fs-policy` returns without calling `next()`, so it owns the slot in the default deployment; a listener registered earlier or with `prepend` would replace that policy. Permission, audit, and sandbox concerns remain on the composable `tools/execute` waterfall.

 The actor is typed `object` in `dsh-fs` — a pure opaque carrier the provider seam never reads or narrows. The owner-derivation (`actor.agent?.session`) and the `{ agent?: { session? } }` structural shape stay entirely inside `dsh-fs-policy`, which narrows the `object` actor to that shape in its listeners. `dsh-fs` owns the event names and the fs vocabulary; it does NOT own the policy layer's runtime owner structure.

@@ -124,7 +122,7 @@ The tool keeps its model-facing schemas (`read`/`write`/`edit`, byte-for-byte un

 The tool passes `exec` (the tool-execution context) as the `actor` argument on every dispatch, so `dsh-fs-policy` can derive its observed-state owner. The tool does not know whether the policy plugin is present: it always provides the bare default behavior in the `next` thunk, and `dsh-fs-policy` short-circuits the thunk before it runs in the default deployment.

-**`fs/observed` fires AFTER the mutation already succeeded**, via a plain `ctx.emit`. The event contract is intentionally narrow: an `fs/observed` listener MUST be synchronous and side-effect-only — `dsh-fs-policy`'s listener is a `WeakMap.set`, which cannot throw under normal operation and returns no promise. The tool does not guard the emit, so a listener that violates the contract by throwing would surface as the tool's `isError` result ([tools/index.ts](../../../../packages/core/tools/src/index.ts) — `ToolRegistry.execute` catches a tool throw into an error result) — reporting failure for a write/edit that actually happened. That is the price of keeping the event a plain fire-and-forget recorder: cordis `emit` does not await listener promises, so async or fallible audit/telemetry/listener work does not belong on this event. If layered or async observation is ever wanted, that is a new event with its own dispatch story.
+**`fs/observed` fires after a successful operation.** Its listeners must be synchronous, non-throwing recorders; the tool does not guard the plain emit, so a throwing listener would report failure after a mutation already succeeded. Async or fallible observation needs a separate event contract.

 ## Policy plugin contract (`dsh-fs-policy`)

@@ -154,7 +152,7 @@ This amends — does not reverse — [the split-fs-seam RFC](../simplification/2

 ## Verification

-The decoupling and its semantics are pinned by tests: a bare-provider config (no `dsh-fs-policy`) boots the `dsh-tool-fs` root plugin and `read`/`write` (create and overwrite)/`edit` work against the real `dsh-fs-local` — an unread edit and an unread overwrite both succeed, proving the tool carries no `fileContext` dependency, while the same operations with `dsh-fs-policy` present are rejected `FS_NOT_OBSERVED` / gated `createIfAbsent`. A second `fs/edit-intent` listener registered after `dsh-fs-policy` is asserted NOT reached (first-wins short-circuit). A stale-read edit reports `FS_STALE_VERSION` through provider CAS, with `dsh-fs-policy` performing no `stat`; the tool's `stat` budget (read = 1, write = 0, edit = 0, on both paths) is asserted directly. Model-facing schemas stayed byte-for-byte unchanged, so snapshot transcript goldens are unaffected.
+Tests pin both paths: without `dsh-fs-policy`, the root tool plugin boots against `dsh-fs-local`, and read, create, overwrite, and unread edit succeed; with the policy, unread edit returns `FS_NOT_OBSERVED` and unread overwrite is gated by `createIfAbsent`. A later intent listener is not reached after the policy decides. Stale edits fail through provider CAS while the policy performs no `stat`; the tool budgets remain one `stat` for read and zero for write or edit on either path. Model-facing schemas remain byte-for-byte unchanged, so snapshots do not change.

 ## Alternatives considered

@@ -6,7 +6,7 @@ Status: implemented

 The hooks subsystem runs external hook commands the way Claude Code and Codex do: a hook is a shell command that receives its event payload as **JSON on stdin** and reads context from a handful of **environment variables** (`CLAUDE_PROJECT_DIR`, `CLAUDE_PLUGIN_ROOT`, `PLUGIN_ROOT`, …). The harness already has a perfectly good command runner behind the `ctx.bash` capability seam ([dsh-bash](../../../../packages/bash/bash) → [dsh-bash-local](../../../../packages/bash/bash-local)), with process-group kills, output truncation/spill, and a credential scrub. Reusing it for hook execution means a hook bridge does not re-implement subprocess plumbing — but the seam had no way to write stdin or set extra env. This RFC adds those two inputs.

-**These fields are NOT a new security boundary.** It is tempting to frame arbitrary-stdin / arbitrary-env as "dangerous, so gate who may use them" — but that framing is wrong, because a model driving the `bash` tool **already** has equivalent power through ordinary shell syntax: `FOO=bar cmd` sets an env var, a heredoc or `printf … | cmd` feeds arbitrary stdin. Adding `env`/`stdin` as seam fields grants the model no capability it lacks. In particular they cannot exfiltrate the harness's ambient credentials: the real control for that is the **credential scrub** in [dsh-bash-local](../../../../packages/bash/bash-local)'s `childEnv()`, which strips `*KEY*`/`*SECRET*`/`*TOKEN*` from `process.env` before the child sees it (see [docs/defensive-patterns.md](../../../defensive-patterns.md) § "Never hand untrusted output the ambient environment or predictable paths"). The scrub works regardless of these fields — a model cannot read a value that is not in the environment, and tool-call arguments are static JSON, never shell-evaluated, so a model cannot write `env: {LEAK: $DEEPSEEK_API_KEY}` and have it expand. So the security question is already answered by the scrub; this RFC is only about giving trusted in-process callers a clean way to pass a JSON payload + `CLAUDE_*` vars without routing them through model-visible shell text.
+`stdin` and `env` do not create a new model capability because ordinary shell syntax already supplies both. Ambient credentials are protected by `dsh-bash-local`'s child-environment scrub, not by hiding these seam fields; model tool arguments are static JSON and do not expand shell variables. The fields therefore serve trusted in-process callers, such as hook bridges, that need to pass structured input and `CLAUDE_*` variables without embedding them in model-visible shell text. See [defensive-patterns.md](../../../defensive-patterns.md) for the ambient-environment rule.

 ## Decision

@@ -14,18 +14,18 @@ Add `stdin?: string` and `env?: Record<string, string>` to **both** `BashExecReq

 Three deliberate choices:

-1. **The model-facing `bash` tool simply does NOT expose `stdin`/`env` as parameters** — not as a security wall, but because bash syntax already covers the model's needs, so duplicating them as tool params would be redundant surface. [dsh-tool-bash](../../../../packages/bash/tool-bash)'s `bash` tool builds its `BashExecRequest` from `command`/`workdir`/`timeoutMs`/`signal`/`owner` only; a model that includes `env`/`stdin` keys in its tool-call arguments simply has them ignored. A regression guard (`tool-bash` "does not forward env/stdin" tests) drives the real tool with those extra args and asserts the recorded request carries neither field — its purpose is to catch a future refactor that blindly spreads `...args` into the request and silently starts forwarding model input into the post-scrub `env` merge, NOT to defend a trust boundary. In-process plugins (the hooks bridges, native plugins) that construct a `BashExecRequest` directly set the fields; the seam imposes no access policy (consistent with how `owner` works — the executor stores but never interprets it).
+1. **The model-facing tool omits `stdin` and `env`.** Shell syntax already covers those needs, so duplicate parameters would add surface without authority separation. The tool builds requests only from declared model arguments, signal, and owner; trusted in-process callers may set the seam fields directly.

 2. **`env` merges AFTER the credential scrub, so an explicit caller entry always wins** — even a credential-shaped name. This is correct because the scrub's job is narrow: stop the harness's *ambient* `process.env` credentials from leaking into a spawned command. A caller that explicitly sets a var has named a value it already holds (not the ambient secret), so the scrub is not a constraint on it. `childEnv(extra?)` layers `scrub(process.env)` → `ENV_OVERRIDES` (the model-friendly `TERM=dumb` etc.) → `extra`, last-wins.

 3. **`stdin`/`env` are required-absent-OK (plain optional) on the resolved spec, NOT required-but-nullable like `owner`.** `owner` is required-but-nullable because a *silently* missing owner yields an unowned, cross-session-readable task — a security footgun that a visible `undefined` guards against. `stdin`/`env` have no such hazard: a missing one means "no stdin / no extra env", which is the safe, ordinary case (every model-driven call). So they stay plain optionals, matching `signal`.

-`dsh-bash-local` spawns stdin as a `'pipe'` (writing the supplied bytes, then closing) ONLY when a caller set `stdin`; with none supplied it uses `'ignore'` — fd 0 → `/dev/null` — the exact pre-seam default. This distinction is observable and deliberate: a closed empty pipe and `/dev/null` are NOT the same file type (node's spawn pipe is an `AF_UNIX` socket, so `test -c /dev/stdin` holds for `/dev/null` but not for an empty pipe), so the no-stdin path — every model-driven call — must keep `/dev/null` rather than regress to an always-open pipe. Each branch's `stdio` tuple is a literal, which preserves the typed `spawn` overload that guarantees non-null `stdout`/`stderr`. When stdin IS written, a child that exits without reading makes the write fail EPIPE; that error is swallowed (the command's outcome rides on its exit code/output, not the write) so it never crashes the host or rejects `done`.
+`dsh-bash-local` creates a stdin pipe only when bytes are supplied; otherwise fd 0 remains `/dev/null`, preserving prior behavior. It writes the bytes and closes the pipe. `EPIPE` from a child that exits without reading is ignored because command exit and output determine the result.

 ## Alternatives considered

-An earlier sketch of this work also proposed making `SENSITIVE_ENV_PATTERN` configurable. Validating against the code, that is **speculative and already subsumed**: `run.ts` documents a configurable whitelist as future work, and the new explicit `env` field — merged after the scrub — already gives a caller full control, including over credential-shaped vars. There is no current caller that needs to *broaden* the ambient scrub (the hazard runs the other way). Adding a config knob now would be a speculative surface with no consumer. If a real workflow ever needs to forward a specific ambient credential, the explicit `env` field is the supported path; a configurable scrub can be reconsidered then.
+**Configurable ambient-secret scrub.** Rejected as speculative. Trusted callers can explicitly provide required values after the scrub without weakening the default ambient protection.

 ## Consequences

-A hook bridge builds a `BashExecRequest` with the hook's JSON payload as `stdin` and its `CLAUDE_*`/`PLUGIN_ROOT` vars as `env`, and runs it through the same `ctx.bash` everything else uses — no bespoke subprocess code, and the full process-group-kill / truncation / spill machinery for free. The model-facing attack surface is unchanged (the credential scrub, not these fields, is what bounds it), and the `bash` tool's request-building stays the single place that decides which fields a model call carries — guarded by a test that fails if a refactor starts forwarding model input. The vocabulary addition is documented in [docs/core-data-structures/bash.md](../../../core-data-structures/bash.md) (the `type-equiv` request/spec blocks) and the three bash-package READMEs.
+Hook bridges pass JSON payloads and hook-specific variables through the existing bash seam, retaining its process-group, truncation, and spill behavior. The model surface remains unchanged, and the bash tool remains the sole owner of model-call request construction. The vocabulary lives in [the bash data-structure reference](../../../core-data-structures/bash.md).
@@ -12,7 +12,7 @@ The harness extends the agent loop through a Cordis event taxonomy (see [the mic

 Two problems motivated pinning the semantics down. First, several turn/step boundaries existed BOTH as a durable `SessionEvent` (`turn/start`, `turn/end`, `step/start`, `step/end`) AND as a mirrored `agent/*` emit (`agent/turn-start`, `agent/turn-end`, `agent/step-start`, `agent/step-end`). A consumer had two sources of truth for the same fact, and every lifecycle change had to update both. Second, the upcoming Hooks subsystem needs ONE coherent, documented surface to subscribe to — a plugin author (and the Claude Code / Codex hook bridges built on top) must know, without reading the loop, whether to listen on a session event or an agent event, and why.

-This is the foundational change in a stack that adds a Hooks subsystem; it establishes the vocabulary the later PRs (interception-Decision reshape, the `hook/*` durable log, the bridges) build on.
+This vocabulary is the foundation for interception decisions, the durable `hook/*` log, and the Claude Code and Codex bridges.

 ## Decision

@@ -6,7 +6,7 @@ Status: implemented

 The ACP bridge gives every session its own workspace: `session/new` records the editor's project directory as `SessionHeader.cwd`, and `dsh-tool-bash` defaults each bash call's `workdir` to the calling agent's `session.header.cwd` (see [the per-session cwd RFC work in `packages/ui/acp`](../../../../packages/ui/acp) and `resolveWorkdir` in `dsh-tool-bash`). So a bash command in session A runs in A's project, and in session B runs in B's — one server process, N workspaces.

-The filesystem tools did NOT honor this. `ctx.fs.resolve(path)` took no caller context, and `dsh-fs-local` resolved every relative path against a single `config.cwd` fixed at plugin load (`process.cwd()`). In the ACP demo that means `write foo.txt` and `bash cat foo.txt` resolve `foo.txt` against **different** directories — the fs tools against the server's launch dir, bash against the session's project dir. The two tools disagree about what "the current directory" is, which is a correctness bug the moment an editor opens any project other than the server's launch dir. It only appeared to work in the snapshot harness because that harness launches the child process in the same temp dir it passes as the session cwd, so the two coincide.
+Filesystem resolution used one plugin-load cwd while bash used the session project directory. Relative paths therefore disagreed whenever the editor project differed from the server launch directory; snapshots hid the bug by making those paths identical.

 ## Decision

@@ -22,7 +22,7 @@ Add a **persisted, tool-private presentation channel** so a tool's `execute` can
 type ToolExecuteReturn = ContentBlock[] | { content: ContentBlock[]; meta?: unknown }
 ```

-`meta` is an opaque payload the core never interprets — typed `unknown` at every seam (the tool that produced it owns and narrows its shape). It MUST be JSON-serializable: the registry threads it onto the `tool/result` **session event**, and `Session.append` runtime-validates all event data with the existing `isJsonValue` predicate, so a non-serializable `meta` is rejected at the source. On replay the same `meta` is read back and handed to `presentResult` via a widened `ToolResult` (`{ content, isError, meta? }`). Because the payload lives in the event log, the diff reproduces on session reload / snapshot replay **for free** — the event-sourcing guarantee, not a re-computation. Typing `meta` as `unknown` (rather than a shared serializable-value type) keeps the tools core free of a dependency it would otherwise take just to name the type, and the runtime `isJsonValue` gate — not the static type — is what actually enforces serializability.
+`meta` is tool-owned `unknown` that the core persists without interpretation. `Session.append` rejects non-JSON values, and replay passes the stored payload back to `presentResult`; presentations therefore reproduce without I/O or recomputation. Runtime validation avoids adding a shared serializable-value dependency to the tools core.

 This is the general shape ("a tool attaches durable result presentation"), not an fs-specific one — any tool can use it.

@@ -31,7 +31,7 @@ This is the general shape ("a tool attaches durable result presentation"), not a
 Per the [capability-seam split](2026-06-13-capability-seams.md), the storage backend returns only **storage facts** and the model-facing tool owns **presentation**:

 - `dsh-fs` widens `FsEditOutcome` with `{ before: string; after: string }` and `FsWriteOutcome` with `{ before: string | null; after: string }` (`before: null` ⇒ a create, or an existing-but-undiffable binary/non-UTF-8 file). The local backend already holds both texts at write time; it returns them as raw LF-normalized text, with **no diff/UI concept** entering the seam.
- `dsh-tool-fs` computes the contextual hunk from before/after and attaches it as `meta: { diffs: FileDiff[] }`. A contextual hunk is computed only when a before-version exists — edit always; write on overwrite; a create has no before, matching `claude-agent-acp`'s empty `structuredPatch` on create. But the completed `tool_call_update` is ALWAYS a `diff` card for a successful mutation: an ACP `tool_call_update.content` REPLACES the call's content, so rendering the model-facing result text would clobber the pending diff. So `write`'s result falls back to an args-derived whole-file diff (`oldText: null`) when it has no contextual hunk (a create, or an overwrite whose content is unchanged), and `edit` — which always changes content — always has a hunk. A failed/aborted/policy-rejected mutation applied nothing, so it carries no `meta` and falls through to the generic error rendering (its message must show).
+- `dsh-tool-fs` stores contextual hunks in `meta: { diffs: FileDiff[] }`. Successful mutations always complete with a diff card because ACP result content replaces the pending card: creates or unchanged overwrites fall back to an args-derived whole-file diff, while edits use applied hunks. Failed mutations carry no diff metadata and render their error normally.

 ### 3. The bridge renders a `diff` result card

@@ -39,7 +39,7 @@ Per the [capability-seam split](2026-06-13-capability-seams.md), the storage bac

 ## Alternatives considered

-**Hand-rolling or vendoring the diff algorithm.** Computing hunks-with-context is a solved problem with sharp edge cases (grouping, context coalescing, the trailing-newline marker). Rather than hand-roll it, `dsh-tool-fs` takes a runtime dependency on the npm [`diff`](https://www.npmjs.com/package/diff) package (a `^9.0.0` range, exact-pinned by the lockfile; it ships its own types) and uses its `structuredPatch`. The repo's default is to vendor Cordis-framework source, but that policy is about the *framework*; a leaf tool package taking a small, well-known, self-typed utility dependency is the same shape as `dsh-acp` depending on `@agentclientprotocol/sdk`. Vendoring a diff algorithm would be re-implementing a battle-tested one for no benefit — the [pre-release "foundation over blast radius"](../../../../AGENTS.md) reasoning does not argue for re-deriving standard algorithms. The dependency's output is normalized in one small module (`packages/fs/tool-fs/src/diff.ts`).
+**Hand-rolling or vendoring the diff algorithm.** Contextual hunks have established edge cases, so `dsh-tool-fs` uses the typed [`diff`](https://www.npmjs.com/package/diff) package and normalizes `structuredPatch` output in one module. The repository's vendoring policy applies to its framework source, not every leaf utility.

 ## Consequences

@@ -8,7 +8,7 @@ Status: implemented

 The immediate pressure came from skill loading: reading an individual `SKILL.md` can already go through `ctx.get('fs')`, but discovering which skill roots contain `<name>/SKILL.md` or `<name>.md` still needs directory enumeration. Adding directory listing only in `dsh-skill` would either keep a direct Node dependency there or invent a one-off local helper outside the filesystem provider stack.

-This branch deliberately lands the provider capability first and does not add a model-facing `ls`/`list` tool or change skill discovery. The follow-up consumer can validate UX and prompt shape separately, while this PR establishes the backend seam and local implementation.
+This decision adds the provider capability without a model-facing `ls`/`list` tool or skill-discovery change. Those consumers require separate UX, prompt, and policy decisions.

 ## Decision

@@ -36,7 +36,7 @@ Broken or disappeared children may be represented as `type: 'other'` without `ve

 ## Alternatives considered

-**Add a model-facing list tool now.** Rejected for this PR. The immediate request is the provider seam, and the user explicitly asked not to change skill loading or other upper layers in this branch. A model-facing tool needs prompt/schema/rendering decisions that should be reviewed separately.
+**Add a model-facing list tool with the seam.** Rejected because its prompt, schema, and rendering contracts are independent of the provider primitive.

 **Keep directory enumeration in each consumer.** Rejected. That would bind product packages such as `dsh-skill` to Node/local filesystem behavior and bypass policy/remote/sandboxed backends.

@@ -24,21 +24,21 @@ The assembled system prompt had four defects, all of one family: facts the harne

 ### Prompt variables

-Plugins contribute named values via `ctx.systemPrompt.variable(name, provider)`; prompt text references them as `{{name}}`. Providers are functions of the `AssembleContext` and may return `undefined` — "no value for THIS assembly". `assemble()` resolves every registered variable into `PromptAssembly.variables` (waterfall listeners can see, add, or override); `renderPrompt` interpolates. Rendering is STRICT — fail loud beats shipping a malformed prompt: a reference to an unregistered name throws (listing what exists; lookup is `Object.hasOwn`, so a prototype property like `{{constructor}}` is unknown, not a function spliced into the prompt), a registered-but-valueless reference throws, a complete `{{…}}` group that is not a well-formed name (`[a-z][a-z0-9_]*`, e.g. `{{ model }}`) throws, and a `{{` that opens no complete group while a `}}` still follows (`{{{model}}}`, `{{a{b}}`) throws. A lone `{{` with no `}}` anywhere after it is ordinary prose and passes through verbatim; substituted values are never re-scanned. Registration rejects duplicate and unreferenceable names, mirroring the tool registry — and `section()` now rejects duplicate section names, making the documented dedup real.
+Plugins register `{{name}}` values through `ctx.systemPrompt.variable(name, provider)`. Assembly resolves them into the waterfall-visible variable map. Rendering rejects unknown own-property references, registered providers that return `undefined`, malformed complete references, and unbalanced references that still contain a closing `}}`; a lone unmatched `{{` remains prose, and substituted values are not rescanned. Registration rejects invalid or duplicate variable names, and section names are unique.

 `dsh-agent-loop` registers the two built-ins, both pure projections of the context agent: `model` (= `options.model`) and `cwd` (= `session.header.cwd`). The example personas write `powered by the {{model}} model` — the model name is stated once, in the `model:` config key. `{{cwd}}` is demonstrated in the ACP example only: every ACP session carries the client's cwd, while config-pre-created stdio agents have none (a persona claiming `{{cwd}}` there fails the turn — by design). The variables stay on the loop plugin (unlike the sections below): they are runtime facts of the agents THIS loop drives, and a replacement loop supplies its own.

 ### Persona as the order-0 section

-`dsh-system-prompt` itself registers the two harness-owned sections (they must survive a swapped loop plugin, so they do NOT live on `dsh-agent-loop`): the static `harness:identity` at order `-100` — every prompt opens by stating the agent is powered by the DeepSeek Harness SDK — and the global default `deployment:persona` at order 0, whose text is the plugin's own `persona` config. `AgentOptions.systemPrompt` and the loop's special-case join are gone: `fullSystemPrompt ≡ renderPrompt(assembly)`, one ordered pipeline for everything the model sees, and `agent/pre-step` (compaction's token-pressure input) measures exactly the real prompt. An agent-scoped section with the same `deployment:persona` name shadows the default for that agent; programmatic setup may register one directly, and the subagent persona feature installs one before publishing an in-process child when the selected provider supports it. Order bands are convention: harness identity `-100`, persona `0`, tool guidance `100–199`; other negative orders also render before the persona.
+`dsh-system-prompt` owns `harness:identity` at order `-100` and the configured `deployment:persona` at order 0, so both survive a replacement loop. Prompt rendering has one path, `renderPrompt(assembly)`, and `agent/pre-step` therefore measures the exact prompt used for compaction. An agent-scoped `deployment:persona` shadows the global default and lets subagent providers install a persona before publication. The conventional order bands are identity `-100`, persona `0`, and tool guidance `100–199`.

 ### Tool guidance ownership

-Per-tool semantics and when-to-use live in tool DESCRIPTIONS, which already ship in every request — the YAML prose was ~fully redundant with them. Sections carry only the cross-call habits a single call's description cannot: `dsh-tool-bash` contributes `tool:bash` (order 105) — check the `[exit code: N]` marker on every result; `dsh-tool-fs`'s read section gains the "not shell commands like cat" contrast. `todo_write` and the subagent tools need NO section — their descriptions already carry the whole contract. The leaf personas shrink to identity + behavior (verify your work; keep answers brief), and the welcome banner stops enumerating tools.
+Per-tool semantics and selection guidance live in tool descriptions. Prompt sections carry only cross-call habits, such as checking bash exit markers or preferring filesystem tools over shell commands. `todo_write` and subagent tools need no section because their descriptions contain the full contract. Deployment personas contain only role and behavior.

 ### The subagent conversation-history descriptor

-`SubagentProvider` gains `readonly inheritsParentContext: boolean` — a DESCRIPTIVE conversation-history fact beside `capabilities`, not in it (capabilities are start-time validation; nothing validates against this flag). Spawn and ACP declare `false`, fork declares `true`. The name refers only to conversation seeding, not Cordis scope, services, tools, or authority. `dsh-tool-subagent` derives both the tool description and the `prompt` parameter description from the flag (`providerWording`): the fork instance now tells the model the child is seeded with the conversation's completed turns (not the in-flight turn) and that its prompt should state only what is new. Deriving the description from a provider that arrives on its own fiber is what forced the provider-lifecycle events and the tool's reactive registration — that mechanism, its Loader-concurrency rationale, and its rejected alternatives are recorded in [the provider-lifecycle-events RFC](2026-07-05-subagent-provider-lifecycle-events.md).
+`SubagentProvider.inheritsParentContext` describes conversation seeding, not scope, services, tools, or authority. Spawn and ACP set it to `false`; fork sets it to `true`. `dsh-tool-subagent` derives its tool and prompt-parameter descriptions from the flag, including that fork inherits completed turns but not the in-flight turn. Provider lifecycle events keep that wording synchronized with reactive provider registration; their rationale lives in the [provider-lifecycle-events RFC](2026-07-05-subagent-provider-lifecycle-events.md).

 ## Alternatives considered

@@ -56,10 +56,10 @@ Per-tool semantics and when-to-use live in tool DESCRIPTIONS, which already ship

 ## Shipped invariants

- `renderPrompt(await assemble(assembleContextFor(agent)))` for the coding-agent example renders the harness identity, then the persona (with the agent's model name interpolated), then the fs/bash/web guidance sections; the loop has no other prompt-composition path.
- The `subagent_fork` schema description says the child inherits the conversation; the `subagent` one says it does not. The tool follows its provider: absent before the backend activates, present after, gone when the backend unloads, re-worded from the fresh provider on reload.
- Unknown/valueless/malformed/unbalanced `{{…}}` references throw with the section name in the message; duplicate section, variable, and tool-name registrations all throw.
- Snapshot goldens are prompt-independent by construction: llm-replay keys replay on (turn, step) chunk streams and never re-verifies the outgoing request.
+- The coding-agent prompt renders identity, persona with the interpolated model, then fs/bash/web guidance through one assembly path.
+- Fork and fresh subagent descriptions reflect whether the provider inherits completed conversation turns; the tool appears, disappears, and is reworded with provider lifecycle changes.
+- Unknown, valueless, malformed, or unbalanced variable references name the section and throw; duplicate section, variable, and tool registrations also throw.
+- Snapshot replay is prompt-independent: it keys recorded chunk streams by turn and step without comparing the outgoing request.

 ## Consequences

@@ -4,7 +4,7 @@ Status: implemented

 ## Problem

-Two gaps shared one root. First, provider KV caching (DeepSeek context caching) is prefix-based — a request pays full price only for the tokens after the longest stored prefix it matches — yet nothing in the request pipeline stated, checked, or measured prefix stability: every registered [`PromptSection`](../../../../packages/core/system-prompt/src/index.ts) happened to be static, the tool set happened not to change mid-session, no listener happened to rewrite requests. A single time-interpolating section would have silently multiplied context cost, and no test or metric would have moved. Second, and deeper: the session log — the system's single source of truth — could not actually answer *what the model saw*. It recorded every message but never the system prompt, the tool schemas, or even which model; the mutable `agent/request` waterfall handed listeners the whole `GenerateOptions` to rewrite per call; replay equivalence was therefore a property of the plugin population, not of the design.
+The request pipeline did not guarantee prefix stability for provider caching, and the session log could not reconstruct what the model saw. It omitted model, system prompt, and tool schemas while allowing per-call request rewrites. Cache behavior and replay equivalence therefore depended on whichever plugins happened to be loaded.

 The reference shape for the happy path is MiniCode's `LLMClient`: a stateful conversation client, appended to — never rebuilt — as the conversation advances, resetting only when the system prompt, tool set, or compaction genuinely changes what the model must see. The design question this RFC answers is how to get that discipline without giving up event-sourcing.

@@ -20,22 +20,22 @@ Prefix-cache stability is corollary #1, not the headline: an append-only log pro

 **Messages.** `Session.deriveMessages()` is cached: each surface node is projected exactly once, when first seen, through the public per-node function `deriveEventMessage(event)`; a surface rewrite (a compaction `replace` — `SurfaceManager.replaceGeneration`) rebuilds. Callers get a fresh array per call over shared, deep-frozen messages: mutating logged history through a projection is unrepresentable (it throws), replacing the old clone-per-call isolation. External reconstructors fold the same public function over a log prefix, so no two paths can disagree.

-**The header.** The request's non-history half — `EpochHeader`: call config (`LlmCallConfig`: model + sampling scalars), rendered system prompt, assembled tool schemas, and the session prefix (`messagePrefix`, below) — is logged session state, in canonical form (empty system/tools/prefix ≡ absent). Two log-only, turn-enclosed events in dsh-session carry it: `request/header`, a full snapshot with reason `'initial' | 'resume' | 'fallback'`, and `request/header-delta`, an amendment (`SystemDelta`: a common-prefix/suffix line trim; `ToolsDelta`: name-keyed added/removed/changed; `config`: replaced whole; `messagePrefix`: replaced whole, an empty array encoding the transition to absence — an arm the loop never exercises in practice, kept for codec totality). The pure trio `foldRequestHeader` / `diffHeader` / `applyHeaderDelta` reconstructs; the live session tracks the fold with the same lazy cursor as the message cache. Snapshots anchor the fold where a fold needs anchors — conversation birth and process boundaries — and each loop instance appends one on its first request (`'initial'` when the log has none, `'resume'` otherwise, even when nothing changed: the boundary itself is a recorded fact, and cross-restart drift becomes attributable while an unchanged header resumes byte-identical). Deltas are an encoding optimization with a safety valve, never a correctness dependency: the writer verifies `applyHeaderDelta(prev, delta)` reproduces the new header exactly and records a `'fallback'` snapshot when the encoding cannot express a change (a pure tool reordering), so a well-formed log always folds.
+`EpochHeader` records the request's non-history state: call config, rendered system prompt, tool schemas, and session prefix, with empty values canonicalized to absence. `request/header` writes a full initial, resume, or fallback snapshot. `request/header-delta` encodes system changes by common-prefix/suffix line trim, tools by name-keyed additions/removals/changes, and config or prefix by full replacement. `foldRequestHeader`, `diffHeader`, and `applyHeaderDelta` are the pure codec. Each loop instance writes a snapshot on its first request to anchor process boundaries. Deltas are only an optimization: the writer verifies round-trip equality and falls back to a full snapshot for unrepresentable changes such as pure tool reordering.

-**The loop, transmission-stateless.** Per step: render assembly (every step — value comparison needs no change-signal discipline, and a section that varies per step surfaces as a *logged* header event per step instead of a silent bust) → on the instance's FIRST step only, the `agent/session-prefix` waterfall — request-ONLY messages fronting the entire derived history (a frozen empty seed, contributions returned as an extension of `next()`; the home for session-stable openers that must NOT become history — a skills catalog, an AGENTS.md digest), deep-frozen and cached on the instance so reuse is structural and the prefix cannot drift mid-session — → `agent/pre-step`, carrying the composed prefix (compaction's surface mutations land before derivation, and its pressure gate counts the prefix this instance will actually send — never a previous instance's logged one, which could under-gate a resumed/forked instance whose contributor grew) → **messages snapshot, then `step/start` appended as the next operation in the same synchronous frame** → seed the call config (first request of the instance: from `AgentOptions`, so explicit options always beat the logged baseline — fork model-overrides and resume reconfiguration stay correct; afterwards: from the folded header) → the `agent/request` waterfall, re-typed `(agent, turn, step, config: LlmCallConfig, next) → LlmCallConfig` — a frozen seed and a returned replacement are ALL a listener shapes; durable content flows through the log channels (`inject()`, steering, prompt-submit `additionalContext`, sections via `system-prompt/assemble`) — → the header event the request owes the log, carrying the prefix as `messagePrefix` (no session event carries it, so the header is its only durable record; resume = a new instance = a recompose, anchored by its `'resume'` snapshot) → build `GenerateOptions` from `messagePrefix + snapshot` + header, deep-freeze (`deepFreeze` exempts the `AbortSignal`, the one live control channel — freezing one breaks `AbortController.abort()`), dispatch. The loop's per-instance bookkeeping is one boolean plus the cached prefix: whether this instance has logged its anchoring snapshot, and what it composed.
+Each step rebuilds prompt assembly. On the instance's first step, `agent/session-prefix` extends a frozen empty seed with request-only opener messages; the result is frozen and cached for that loop instance. `agent/pre-step` then receives the composed prefix before messages are snapshotted immediately ahead of `step/start`. The first call config starts from explicit `AgentOptions`, preserving fork overrides and resume reconfiguration; later calls start from the folded header. `agent/request` may replace only that frozen config seed, while model-visible content enters through logged channels. The loop records the owed header event—the prefix's only durable home—builds `GenerateOptions` from prefix, snapshot, and header, and deep-freezes it while leaving `AbortSignal` live. Per-instance state is only the cached prefix and whether its anchoring snapshot has been written.

-**The reconstruction boundary is `step/start`, unconditionally.** A step's messages are the derivation over `events[0..stepStartSeq)`. Because the snapshot precedes the `step/start` append in the same synchronous frame, an `agent.inject()` from an `agent/request` listener or any concurrent task lands after the boundary and joins the NEXT request. `session/event` is observe-only during publication: a reentrant append is rejected until the current callback list drains, preventing nested event delivery from overtaking the event being observed. `agent/pre-step` is the sanctioned seam for content that must affect the CURRENT request. A step's header for reconstruction is the fold after its own `request/header*` event (which sits between its `step/start` and first response event) or the fold carried forward.
+**`step/start` is the reconstruction boundary.** A step derives messages from events before that sequence. Injection after the snapshot joins the next request, and reentrant appends are rejected during event publication. `agent/pre-step` is the seam for content needed by the current request. Header reconstruction folds through the step's own `request/header*` event, or carries the prior fold when no new header is written.

-**Enforcement.** Dev-mode ([dsh-invariants](../../../../packages/support/invariants/src/index.ts)), on `llm/stream`: a frozen request with a live `sessionId` — the loop-built marker; hand-built one-shots are unfrozen and skipped — must carry messages deep-equal to the folded header's `messagePrefix` followed by the boundary derivation — the derivation rebuilt through a FRESH `Session` over `events[0..stepStartSeq)` so the live cache cannot vouch for itself — and header fields equal to `foldRequestHeader` over the log. There is no divergence allowance and nothing to allow: no seam can put unlogged content into a request — the `agent/session-prefix` seam's product enters only because the header event records it first. `prepend: true` only defends against the replay adapter's short-circuit (an append-registered listener); two prepended listeners have no defined mutual order in cordis, so correctness rests on the seq-bounded fold, never on listener timing. Measurement stays lean: the with-key e2e ([request-cache.e2e.ts](../../../../packages/core/agent-loop/tests/request-cache.e2e.ts)) proves `usage.cacheReadTokens > 0` on every request after the first against the live API, and per-step usage in the log is the production observable — a header event or compaction shows up as a cache-read collapse on the next step.
+**Enforcement.** In development, `dsh-invariants` independently rebuilds each loop request through a fresh `Session`, so the live cache cannot vouch for itself, then compares messages and folded header fields at `llm/stream`. Loop requests are identified by their frozen shape and session id; direct one-shots are excluded. Correctness depends on sequence-bounded reconstruction rather than listener order. A with-key e2e requires positive cache-read tokens after the first request; per-step usage is the production signal, and a header change or compaction appears as a cache-read drop on the next step.

 ### The MiniCode shape: adopted, with the provenance arrow inverted

-What survives from `LLMClient`: the conversation is maintained, not rebuilt — one projection per message, ever; requests advance append-only; resets happen only for a system-prompt/tool change, a config change, or compaction, each now a *logged* fact. What is deliberately inverted: MiniCode's client is the source of truth and its event stream derives from client appends (`on_event(MessageAdded)`), which suits an advisory event stream. Here the log is contractual — persistence, crash recovery, fork seeding, transcript rendering, and the snapshot harness all replay it — and it carries strictly more than a message list (turn/step boundaries, raw chunk streams, tool-call pairing, provenance, log-only records), so a message-list client cannot generate it. The arrow therefore points log → client: the conversation state IS the log plus two cached folds inside `Session` (messages, header), and the "client" the loop talks to is the session itself. What the inversion buys over the original: the reconstruction is *checkable* against an independent record on every request — MiniCode's client has nothing to check itself against.
+Like MiniCode, the conversation advances append-only and resets only when model-visible state changes. Unlike MiniCode, the event log remains the source of truth because it also owns persistence, recovery, boundaries, tool pairing, and provenance. `Session` caches message and header folds derived from that log, making every request independently checkable.

 ## Alternatives considered

 - **Client as source of truth** (literal MiniCode): a second operative truth beside the log — the two drift and nothing notices; see the section above.
- **A stateful transmission client mirroring the log** (a `PromptPrefix` class holding committed/open message zones with an append/editTail/reset vocabulary, the log pushed into it per event): behaviorally equivalent on the happy path, but it duplicates conversation state outside the session, needs transactional rollback around listener seams, keeps an unlogged content-shaping surface (`editTail`) whose divergence the invariant must specially allow, and still cannot answer "what header did the model see" from the log. Dissolving it into the session's own caches plus logged header events made every one of those problems unrepresentable instead of guarded. (PR #162 is the archaeology of this alternative, three designs deep.)
+- **A stateful transmission client mirroring the log** — duplicates conversation state, needs rollback around listeners, leaves an unlogged edit surface, and still cannot reconstruct request headers. Session-owned caches plus logged headers avoid those split truths.
 - **Per-call request scalars** (a freely mutable config handed to each `agent/request` dispatch): a listener flips the model per call with zero accounting, silently abandoning the provider cache this design exists to protect. Config is per-conversation logged state; the waterfall proposes, the log records.
 - **Detect-and-report** (compare consecutive requests, warn on divergence): catches violations after the fact; a violating request is still constructible and ships. Rejected for interface-level unrepresentability.
 - **Event-driven assembly** (re-render only on change signals): a missed-signal bug class — a tool registered mid-session emits `tools/change`, not `system-prompt/change`, and a third-party provider may emit nothing. Per-step render + value compare is robust with zero signal discipline.
@@ -6,7 +6,7 @@ Status: implemented

 [The prompt-variables RFC](2026-07-05-prompt-variables-and-tool-guidance-ownership.md) makes `dsh-tool-subagent` DERIVE its model-facing wording from its provider: `SubagentProvider.inheritsParentContext` (spawn/ACP `false`, fork `true`) drives both the tool description and the `prompt` parameter description (`providerWording`), so the fork tool stops lying about context inheritance. That fix created a cross-fiber data dependency: a tool's description is fixed at TOOL REGISTRATION (deliberately — the description is where tool-choice guidance lives), but the provider arrives on its own plugin fiber, on no particular schedule.

-The first implementation resolved the provider at the tool plugin's `apply` time and threw when it was absent — an implicit load-order requirement ("list the backend before the tool in cordis.yml"). Review reproduced the failure that requirement hides: the cordis Loader starts sibling entries CONCURRENTLY (`Promise.all` over the group) and `Entry.init()` does not await activation, so a backend whose activation is delayed leaves the tool's fiber permanently failed even when "listed first". The ordering the requirement leaned on is not a contract the Loader offers — "async state is not synchronous state" ([defensive patterns](../../../defensive-patterns.md)).
+Resolving the provider at the tool plugin's `apply` time creates an implicit load-order requirement ("list the backend before the tool in cordis.yml"). That requirement fails because the Cordis Loader starts sibling entries concurrently and `Entry.init()` does not await activation: a delayed backend can leave the tool fiber failed even when listed first. The Loader offers no sibling-order guarantee — "async state is not synchronous state" ([defensive patterns](../../../defensive-patterns.md)).

 ## Decision

@@ -21,7 +21,7 @@ The events also complete the seam's vocabulary: `ctx.subagents` is a named regis

 ## Alternatives considered

- **Resolving the provider at `apply` time and throwing when absent (a load-order requirement)** — the first implementation, rejected after review reproduced the failure above. Documenting the requirement ("list backends first") would pin a guarantee the Loader does not make.
+- **Resolve the provider at `apply` time and throw when absent** — rejected because "list backends first" would claim a Loader ordering guarantee that does not exist.
 - **Retrying the lookup (poll until the provider appears)** — converges eventually but invents a private readiness protocol beside the one the framework already has (effect registration + disposal); it also cannot notice a provider LEAVING, so HMR would strand a tool whose wording describes a disposed backend.
 - **Section-only subagent wording, lazily resolved at assemble time** — tolerates any load order too, but moves tool-choice guidance out of the DESCRIPTION, contradicting the ownership rule the prompt-variables RFC establishes (per-tool semantics and when-to-use belong in the description). Reactive registration keeps the description authoritative AND order-free.
 - **Keying wording off the provider NAME instead of the provider object** — `providerName` is itself config, so a renamed provider silently gets the wrong words; deriving from the resolved provider's own `inheritsParentContext` cannot drift.
@@ -29,6 +29,6 @@ The events also complete the seam's vocabulary: `ctx.subagents` is a named regis
 ## Consequences

 - Consumers deriving state from a named provider react to `subagent/provider-added`/`-removed` instead of reading the registry at `apply` time; `dsh-tool-subagent` is the reference implementation.
- **The two emits carry asymmetric failure semantics, deliberately.** `provider-removed` fires inside the registration's disposer and is delivered with PER-LISTENER containment (the service's `emitLifecycle`, not raw `ctx.emit`, which halts dispatch on the first throw): a throwing subscriber is logged, never starves a later mirror into holding a stale tool, and never disrupts the backend fiber's teardown — dispose reaches quiescence. `provider-added` propagates: it fires at registration time, where a throwing listener unwinds the yielded rollback — the same fail-loud register-time semantics as the system-prompt registries. The run-time backstop bounds what a stale mirror could cost anyway: `start()` re-resolves the provider by name per run, so a tool that outlived its provider fails that call cleanly instead of dispatching into a dead backend. The [events catalog](../../../cordis-catalog/events.md) carries the exact signatures, and the [producer/consumer map](../../../event-producer-consumer.md) shows `dsh-subagent` emitting and `dsh-tool-subagent` consuming both events.
+- **Addition fails loud; removal is contained per listener.** An addition listener may unwind registration. Removal runs during disposal, so one throwing listener is logged without starving later mirrors or disrupting teardown. `start()` still resolves the provider by name for every run, preventing stale tools from calling a removed backend. See the [events catalog](../../../cordis-catalog/events.md) and [producer/consumer map](../../../event-producer-consumer.md).
 - **A window where the tool is absent.** Between backend disposal and re-registration (an HMR reload), the model sees no subagent tool. This is the honest state — the alternative is a tool that dispatches into nothing — and the tool registry's `tools/change` emit keeps prompt assembly current.
 - **Two waiting fibers sharing a `toolName` is an invalid config caught late.** If two loads of `dsh-tool-subagent` name different providers but the same `toolName`, both wait, and whichever provider arrives first registers; the second registration throws only when ITS provider arrives. `TODO(subagent-dup-toolname)` in the plugin records this blast radius; the tool registry's duplicate-name rejection remains the backstop.
@@ -12,8 +12,6 @@ Timeout handling was drifting apart across the tool-bearing capabilities, and th

 Each new external-process or network tool re-derived the same four things — clamp the requested value, start a timer, fuse the timeout with upstream cancellation, and distinguish "timed out" from "cancelled" on the way out — and the fusion and reason-recovery are exactly the parts that are easy to get subtly wrong (web_fetch's `signal.reason` dance is evidence). At the same time, the *termination* each performs is irreducibly different: bash kills an OS process group (work runs in a child process, outside this runtime, reachable only by signal), while web aborts an in-process `fetch` (undici tears down the socket). There is no single mechanism that can stop all of them.

-The two reference agents surveyed converged on the same split. Codex models "what will end this exec early" as one value (`ExecExpiration`, an enum fusing timeout and a cancellation token) whose `wait_with_outcome()` returns `TimedOut | Cancelled`, while the actual `kill_process_group` lives outside it — and that abstraction is reused *only* across the exec family, with MCP, model-stream, and guardian each keeping their own bespoke `tokio::time::timeout`. Claude Code shares nothing: bash and ripgrep each own a private SIGTERM→SIGKILL kill and distinguish timeout from cancellation by throwing distinct error types, while file I/O has no timeout. Both confirm the boundary drawn here: the timing-and-classification half is worth sharing within a family of like-terminated operations; the termination half is not shareable and stays in each capability.
-
 ## Decision

 `@deepseek-ai/dsh-timeout` lives under `packages/util/` (peer to `dsh-brand`) and owns the *timing and classification* half of timeout; the *termination* half — the hard kill — stays in each capability's implementation. It is a library of pure functions, **not** a cordis service or plugin: it takes no `ctx`, registers nothing, holds no cross-call state, and emits no events. There is deliberately no central "timeout service" that would have to know how to stop every capability's work — that knowledge is exactly what a microkernel keeps out of shared layers, and what Codex's exec-only `ExecExpiration` scope demonstrates.
@@ -57,7 +55,7 @@ export function deadline(
 export function timeoutOf(x: AbortSignal | { reason?: unknown }, code?: string): TimeoutReason | undefined
 ```

-`deadline` is `AbortSignal.any([upstream, <timeout controller>])` with three things the standard library does not give: a typed, identifiable `TimeoutReason` on the timeout abort (native `AbortSignal.timeout()` yields a fixed `TimeoutError`, indistinguishable across timeout kinds), an internal `timeoutMs <= 0` "no timeout" sentinel for backend-owned background work, and a `Symbol.dispose` cleanup that works with both `using` and manual disposal. `AbortSignal.any` is a Node ≥ 20 primitive; it is the single mechanism that fuses two abort sources into one, adopting the reason of whichever fires first. External request hints validate as positive finite numbers via `clampTimeout` before they reach `deadline`; `0` is not a model-/plugin-facing "disable timeout" value. When `timeoutMs <= 0` and no upstream signal is present, `deadline()` returns a never-aborting signal plus a no-op disposer so callers keep one call shape. `TimeoutReason` is an internal classification reason: providers translate it into seam-specific public errors or result fields before returning to callers. `timeoutOf`'s optional `code` scopes classification to the caller's own deadline: when the `upstream` is itself a deadline (a future `tools/execute` middleware arming a per-call deadline), `AbortSignal.any` preserves the outer `TimeoutReason` if it fires first, and an unscoped match would misreport the outer timeout as the inner capability's own; scoping to `code` reads a foreign timeout as an ordinary upstream cancel.
+`deadline` fuses an upstream signal with a timer through `AbortSignal.any`, adds a typed `TimeoutReason`, and exposes disposable timer cleanup. Non-positive timeouts are an internal no-timeout sentinel for backend-owned background work; external hints pass through `clampTimeout` and must be positive and finite. Without a timer or upstream signal, the function returns a never-aborting signal with the same disposal shape. Providers translate timeout reasons into seam-specific results. `timeoutOf(signal, code)` scopes classification so an outer nested deadline is treated as upstream cancellation rather than the inner capability's timeout.

 ### The division of labor

@@ -76,7 +74,7 @@ The signal only *notifies*; termination is always the listener's job, and the li
 ### How each capability consumes it

 - **web_fetch** — the tool stays validate-and-forward; the provider's hand-rolled controller + `setTimeout` + manual listener + `finally` + `signal.reason` recovery is replaced by provider-owned `deadline`/`timeoutOf`. A pre-aborted upstream signal still throws `WEB_ABORTED` up front; otherwise `fetch` runs against the fused `d.signal`, and `translateAbortOrNetwork` classifies a thrown error by the signal (`timeoutOf` → `WEB_FETCH_TIMEOUT`, else aborted → `WEB_ABORTED`, else network → `WEB_PROVIDER_ERROR`). The public error-code contract is unchanged, and `TimeoutReason` never crosses the web seam as the public error.
- **bash** — `resolve()` stays a pure request-to-spec step: it clamps with `clampTimeout(request.timeoutMs, config.timeoutMs, config.maxTimeoutMs, 'bash-local: request.timeoutMs')` and carries `request.signal` through unchanged. Foreground `run()` owns the timeout: `using d = deadline(spec.signal, spec.timeoutMs, 'BASH_TIMEOUT')`, then `runBash` receives only `d.signal`. `runBash` no longer owns any timer — it listens for abort and runs its existing SIGTERM→grace→SIGKILL process-group kill, and its `SpawnSpec`/`SpawnOutcome` no longer carry `timeoutMs`/`timedOut`/`aborted` (the executor classifies from the deadline signal instead). `run()` computes `timedOut = timeoutOf(d.signal, 'BASH_TIMEOUT') !== undefined` and `aborted = d.signal.aborted && !timedOut`, so the public seam booleans (`BashRunResult.timedOut`/`aborted`) are mutually exclusive — the shared deadline reports the cause that first cut the command short, and the `code` scope keeps a nested outer deadline from being misread as bash's own timeout. Background `start()` creates no deadline and forwards only the upstream signal, so background tasks stay timeout-free; a task's killed-vs-completed status reads its own `spec.signal.aborted`.
+- **bash** — `resolve()` clamps the request into an explicit spec. Foreground `run()` creates the deadline and passes its signal to process execution, whose existing abort listener performs the process-group kill. The executor classifies the first abort as timeout or cancellation. Background starts remain timeout-free and forward only upstream cancellation.

 ## Consequences

@@ -95,4 +93,4 @@ Out of scope, named to mark the boundary: `web_search` can gain an optional mode

 **A `withTimeout(promise, ms)` wrapper instead of a signal factory.** Rejected because racing a promise against a timer resolves the *tool-call* promise on deadline without stopping the underlying work — the child process or fetch socket leaks on. Handing out a signal and requiring the capability to listen is what forces a real termination path to exist. This mirrors the "dispose must reach quiescence, not just request it" defensive rule.

-**Keep bash's two independent triggers (`killTimer` + `onAbort`) rather than fusing.** Rejected for the convergence goal: fusing into one `deadline` signal removes bash's bespoke timer and gives every capability one shape. The trade-off is that bash's `timedOut`/`aborted` booleans become first-abort classifications rather than independent facts that can both be true when timeout and user abort race before process close. That is acceptable because the result reports the cause that first cut the command short; the termination action stays the same uniform SIGTERM→grace→SIGKILL kill. Note the deliberate non-alignment with Codex: Codex forks its kill by outcome (timeout → immediate SIGKILL; cancel → SIGTERM + 50 ms grace → SIGKILL), whereas the fused signal drives one uniform `kill()` for both, matching Claude Code's unified bash kill. Splitting the kill by `timeoutOf` is possible later if a need appears; there is none now.
+**Keep separate bash timeout and cancellation triggers.** Rejected because one deadline signal removes the bespoke timer and standardizes classification. Racing causes report whichever abort arrived first, while the existing SIGTERM-to-SIGKILL termination path remains unchanged.
@@ -50,7 +50,7 @@ The plugin is `@deepseek-ai/dsh-timeout-policy`, a zero-config function/namespac
    searchTimeoutMs: 30000
 ```

-Keeping the tool name out of this plugin's config is deliberate: a budget keyed by a free-text tool name could be mistyped (`web_fech`) and then silently apply to nothing. Declaring `timeoutMs` on the tool makes that failure class structurally impossible — the enforcer reads `ctx.tools.get(exec.name)?.timeoutMs`, and `exec.name` is the tool being dispatched, so the lookup always resolves and there is no unknown-name path to warn or throw about. `timeoutMs` is validated positive-finite by `defineTool` at definition time. For a tool that declares a budget the listener arms `deadline(exec.signal, timeoutMs, 'TOOL_TIMEOUT')`, swaps the derived signal onto `exec` for the downstream dispatch, restores the caller's own signal afterward, and returns a structured `TOOL_TIMEOUT` result when `timeoutOf(d.signal, 'TOOL_TIMEOUT')` matches. A tool with no declared budget delegates unchanged.
+Timeouts live on tool definitions rather than a free-text name map, eliminating misspelled unused policy. `defineTool` validates a positive finite budget. During dispatch the enforcer derives a deadline signal, restores the caller signal afterward, and converts its own expiry into `TOOL_TIMEOUT`; tools without a budget pass through unchanged.

 Signal replacement is by **in-place mutation of `exec.signal`**, not by passing a new object to `next()`. Cordis's waterfall `next()` ignores any arguments handed to it and re-invokes downstream listeners with the shared payload array (`vendor/cordis/src/events.ts`), so the documented cordis idiom — mutate the shared object, then delegate — is the only mechanism that reaches dispatch. The plugin restores `exec.signal` to the caller's original in a `finally` so `tools/post-execute` never sees this plugin's (possibly already-aborted) deadline signal.

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-10-single-file-executable-sdk-runtime-distribution.md: 4170d9f63773ef998bc5393fabc98a2b9fcba2fa
-2026-07-10-single-file-executable-sdk-runtime-distribution.zh.md: 7d80fb572ea36010df4829121fabe8cf66944f6b
+2026-07-10-single-file-executable-sdk-runtime-distribution.md: 372058dc04c4a36e82f5a5a6f5ef1af48068e4e3
+2026-07-10-single-file-executable-sdk-runtime-distribution.zh.md: cd12a65d185e8cdeafc4d04faad4a3349c6150d4
@@ -42,7 +42,7 @@ The deploy root is [`python/sdk-runtime/package.json`](../../../../python/sdk-ru

 [`scripts/build-exe-for-python-sdk.ts`](../../../../scripts/build-exe-for-python-sdk.ts): runtime closure verification → `pnpm run build` → (after clearing) `pnpm --filter dsh-jsonrpc-agent-pkg deploy --legacy --prod --config.node-linker=hoisted --config.auto-install-peers=false --config.link-workspace-packages=true` **directly into** `python/sdk-runtime/src/deepseek_harness_runtime/runtime/node/` → inject the pkg configuration (`bin` points at `node_modules/@deepseek-ai/dsh-jsonrpc-agent/lib/bin.js` inside the closure, `assets` is a full glob — dynamic import is invisible to pkg's static analysis, so everything must be packed in explicitly) → one `pkg --sea` per target → the executables `dsh-jsonrpc-agent-pkg-<platform>-<arch>` land in `dist-exe/` and are copied back into the runtime directory. CI treats them as intermediate test inputs and retains their platform wheels. All four deploy flags are grounded in measurement: `--legacy` is the mandatory path with inject-workspace-packages off; hoisted yields a zero-symlink file tree (most stable for the pkg VFS, physically guaranteeing a single cordis instance); disabling automatic peer installation keeps unpublished package names from triggering registry resolution; link-workspace-packages points the closure at workspace/vendor sources.

-CI: [`.github/workflows/build-exe-for-python-sdk.yml`](../../../../.github/workflows/build-exe-for-python-sdk.yml), triggered explicitly only — `workflow_dispatch`, or the `build-exe` label on a pull request; native builds on the three platforms linux-x64 / linux-arm64 (`ubuntu-24.04-arm`) / macos-arm64, with `~/.pkg-cache` cached; macOS ad-hoc signing is handled by pkg. Each leg drives a mock SSE model through the SDK with the default config and a custom `cordis.yml`, drives the exe directly over NDJSON JSON-RPC, verifies the JSONL and final response, and installs release-shaped wheels into a clean venv without `runtime_bin`; Linux additionally inspects GLIBC requirements and runs in a manylinux 2.28 container. The run retains only four artifacts, each containing one release file: the platform-independent SDK wheel and the three native runtime wheels; bare executables and source bundles remain intermediate test inputs. [`.gitlab-ci.yml`](../../../../.gitlab-ci.yml) accepts only `python-vX.Y.Z` tag pipelines whose version matches the root `package.json`, builds one SDK wheel and three native runtime wheels, then a single serialized job checks and publishes all four to the project PyPI registry. Windows is a non-goal.
+CI: [`.github/workflows/build-exe-for-python-sdk.yml`](../../../../.github/workflows/build-exe-for-python-sdk.yml), triggered explicitly only — `workflow_dispatch`, or the `build-exe` label on a pull request; native builds on the three platforms linux-x64 / linux-arm64 (`ubuntu-24.04-arm`) / macos-arm64, with `~/.pkg-cache` cached; macOS ad-hoc signing is handled by pkg. Each leg drives a mock SSE model through the SDK with the default config and a custom `cordis.yml`, drives the exe directly over NDJSON JSON-RPC, verifies the JSONL and final response, and installs release-shaped wheels into a clean venv without `runtime_bin`; Linux additionally inspects GLIBC requirements and runs in a manylinux 2.28 container. A full three-target run retains four artifacts, each containing one release file: the platform-independent SDK wheel and three native runtime wheels; a subset dispatch retains the SDK wheel and selected runtime wheels. Bare executables and source bundles remain intermediate test inputs. [`.gitlab-ci.yml`](../../../../.gitlab-ci.yml) accepts only `python-vX.Y.Z` tag pipelines whose version matches the root `package.json`, builds one SDK wheel and three native runtime wheels, then a single serialized job checks and publishes all four to the project PyPI registry. Windows is a non-goal.

 ### Python SDK distribution: two carriers, exe for production, node for development

@@ -42,7 +42,7 @@ exe 的 VFS 内是**构建产物形态的真实包树**（各包的 `lib/` + 真

 [`scripts/build-exe-for-python-sdk.ts`](../../../../scripts/build-exe-for-python-sdk.ts)：运行时闭包校验 → `pnpm run build` →（清空后）`pnpm --filter dsh-jsonrpc-agent-pkg deploy --legacy --prod --config.node-linker=hoisted --config.auto-install-peers=false --config.link-workspace-packages=true` **直接写入** `python/sdk-runtime/src/deepseek_harness_runtime/runtime/node/` → 注入 pkg 配置（`bin` 指向闭包内的 `node_modules/@deepseek-ai/dsh-jsonrpc-agent/lib/bin.js`；`assets` 使用全量 glob，因为动态 `import()` 对 pkg 静态分析不可见，必须显式打入全部内容）→ 每个构建目标调用一次 `pkg --sea` → 可执行文件 `dsh-jsonrpc-agent-pkg-<platform>-<arch>` 写入 `dist-exe/`，并拷回运行时目录。CI 将这些文件作为测试中间输入，只保留对应平台的 wheel 包。四个部署标志都有实测依据：未启用 `inject-workspace-packages` 时必须使用 `--legacy`；`hoisted` 产出无符号链接的文件树（对 pkg VFS 最稳定，并从物理上保证只有一个 Cordis 实例）；关闭对等依赖自动安装可避免未发布包名触发注册表解析；`link-workspace-packages` 让闭包指向工作区/vendor 源码。

-CI 使用 [`.github/workflows/build-exe-for-python-sdk.yml`](../../../../.github/workflows/build-exe-for-python-sdk.yml)，且只允许显式触发：手动派发 `workflow_dispatch`，或给 PR 添加 `build-exe` 标签。linux-x64、linux-arm64（`ubuntu-24.04-arm`）和 macos-arm64 三个平台分别进行原生构建，并缓存 `~/.pkg-cache`；macOS 的 ad-hoc 签名由 pkg 处理。每个平台都使用模拟 SSE 模型，分别通过默认配置和自定义 `cordis.yml` 驱动 SDK，再通过 NDJSON JSON-RPC 直接驱动 exe，校验 JSONL 与最终响应；最后把发布形态的 wheel 包安装到干净的 venv 中，并在不传 `runtime_bin` 的情况下运行。Linux 还会检查 GLIBC 依赖，并在 manylinux 2.28 容器中运行。整次运行只保留 4 个产物，每个产物只含一个发布文件：平台无关的 SDK wheel 包和 3 个原生运行时 wheel 包；裸 exe 与源码包只作为测试中间输入。[`.gitlab-ci.yml`](../../../../.gitlab-ci.yml) 只接受版本与根目录 `package.json` 匹配的 `python-vX.Y.Z` 标签流水线，构建一个 SDK wheel 包和 3 个原生运行时 wheel 包，再由单个串行任务校验并将这 4 个文件发布到项目的 PyPI 注册表。Windows 不在目标范围内。
+CI 使用 [`.github/workflows/build-exe-for-python-sdk.yml`](../../../../.github/workflows/build-exe-for-python-sdk.yml)，且只允许显式触发：手动派发 `workflow_dispatch`，或给 PR 添加 `build-exe` 标签。linux-x64、linux-arm64（`ubuntu-24.04-arm`）和 macos-arm64 三个平台分别进行原生构建，并缓存 `~/.pkg-cache`；macOS 的 ad-hoc 签名由 pkg 处理。每个平台都使用模拟 SSE 模型，分别通过默认配置和自定义 `cordis.yml` 驱动 SDK，再通过 NDJSON JSON-RPC 直接驱动 exe，校验 JSONL 与最终响应；最后把发布形态的 wheel 包安装到干净的 venv 中，并在不传 `runtime_bin` 的情况下运行。Linux 还会检查 GLIBC 依赖，并在 manylinux 2.28 容器中运行。完整构建三个目标时保留 4 个产物，每个产物只含一个发布文件：平台无关的 SDK wheel 包与 3 个原生运行时 wheel 包；手动选择部分目标时保留 SDK wheel 与所选运行时 wheel。裸 exe 与源码包只作为测试中间输入。[`.gitlab-ci.yml`](../../../../.gitlab-ci.yml) 只接受版本与根目录 `package.json` 匹配的 `python-vX.Y.Z` 标签流水线，构建一个 SDK wheel 包和 3 个原生运行时 wheel 包，再由单个串行任务校验并将这 4 个文件发布到项目的 PyPI 注册表。Windows 不在目标范围内。

 ### Python SDK 分发：双载体，exe 用于生产，`node` 用于开发

@@ -26,7 +26,7 @@ The design can be skimmed as seven choices:
 | Compose the model-visible prompt and tool surface | One shared tool view plus the authoritative assembly-waterfall result |
 | Coordinate subagent, worker, and process shutdown | One cancellation signal plus the independent terminal/quiescence facts of that boundary |

-The rest of this RFC expands those choices in dependency order. It first explains the Cordis mechanics, then scope routing, creation and session commit, tools and prompts, subagents and workflows, and finally the checks that make the reasoning executable.
+The rest of this RFC expands those choices in dependency order: Cordis mechanics, scope routing, creation and session commit, tools and prompts, subagents and workflows, then executable checks.

 The [July 8 RFC](2026-07-08-agent-scope-contexts.md) remains the contributor contract. The separate [subagent composition-controls RFC](../feature/2026-07-12-subagent-persona-tool-filter-and-depth.md) owns `persona`, `toolFilter`, and `maxDepth`; this document discusses only how their setup fits the lifecycle.