feat(subagent): add explicit child reports

.agents/notes/implemented/feature/2026-07-28-continuable-subagent-conversations.md

@@ -34,7 +34,7 @@ The continuation manager owns activation admission, authority checks, the live o
 
 ### Materialization and public operations
 
-The named subagent provider participates only in preparing the initial creation spec, where `spawn` and `fork` differ. Its optional `prepareContinuable(request): Promise<ContinuableCreateSpec>` method is the continuable-creation capability. The returned spec contains only detached provider-specific creation inputs such as the optional parent-history seed; it contains no Agent, `AgentHandle`, prompt delivery, result, disposal, or resume operation. The manager reserves the child identity, resolves the durable descriptor and common Agent setup, calls `ctx.agents.create()` through a private activation-owner scope, installs the returned `AgentHandle` into the Activation, establishes any continuable-parent ownership, and then calls `Agent.followup(initialPrompt)`. Inbox acceptance yields an `MessageId`; at that boundary `ctx.subagents.startContinuable()` returns `{ childId, messageId }` without waiting for the turn to start or for the message to enter the Session log.
+The named subagent provider participates only in preparing the initial creation spec, where `spawn` and `fork` differ. Its optional `prepareContinuable(request): Promise<ContinuableCreateSpec>` method is the continuable-creation capability. The returned spec contains only detached provider-specific creation inputs such as the optional parent-history seed; it contains no Agent, `AgentHandle`, prompt delivery, result, disposal, or resume operation. The manager reserves the child identity, resolves the durable descriptor and common Agent setup, calls `ctx.agents.create()` through a private activation-owner scope, installs the returned `AgentHandle` into the Activation, establishes any continuable-parent ownership, and then calls `Agent.followup(initialPrompt)`. Inbox acceptance yields a `MessageId`; at that boundary `ctx.subagents.startContinuable()` returns `{ childId, messageId }` without waiting for the turn to start or for the message to enter the Session log.
 
 Any failure before inbox acceptance rejects without returning either id. Agent creation provides rollback before handle transfer; after transfer, the manager keeps one closing transaction visible to concurrent delivery and drain, disposes the created handle, removes the Activation, and rolls back any parent `ownedChildren` membership before rejecting. Failure before the residency start edge publishes no terminal edge, while failure after a published start closes the lifecycle pair through normal disposal.
 
@@ -44,7 +44,7 @@ Cold resume does not dispatch through a subagent provider. The continuation mana
 
 `SubagentProvider.start()` and `SubagentRun` remain exclusively on the unchanged one-shot path. A continuable Activation directly owns its `AgentHandle` and never creates, wraps, or retains a `SubagentRun`; `SubagentRun.steer?()` is therefore absent.
 
-`ctx.subagents.followup(parent, childId, content, { source, signal })` remains the sole continuation-message operation. The exact live parent Agent authorizes delivery; cold resume checks that authority before reconstruction and every path checks it again in the final no-await inbox-admission span, so a parent unregistered or replaced during materialization cannot authorize delivery. `source` remains durable provenance and grants no authority. The model-facing `send_message` tool keeps only its stable `subagent_id` and `message` fields and always submits a follow-up turn. Both start and follow-up return the accepted `MessageId`, and neither reports how the manager materialized the Activation.
+`ctx.subagents.followup(parent, childId, content, { source, signal })` remains the sole parent-to-child continuation-message operation. The exact live parent Agent authorizes delivery; cold resume checks that authority before reconstruction and every path checks it again in the final no-await inbox-admission span, so a parent unregistered or replaced during materialization cannot authorize delivery. `source` remains durable provenance and grants no authority. The model-facing `send_message` tool keeps only its stable `subagent_id` and `message` fields and always submits a follow-up turn. Both start and follow-up return the accepted `MessageId`, and neither reports how the manager materialized the Activation.
 
 For start and follow-up, the caller signal owns lookup, materialization, and admission only until inbox acceptance. After the operation returns its `MessageId`, the manager owns the Activation independently; later caller cancellation does not cancel the accepted turn or dispose the child.
 
@@ -111,11 +111,9 @@ Top-level teardown is host-owned rather than represented as another Activation.
 
 The activation-owner scope exists because ordinary Cordis owner effects unwind in reverse registration order, which cannot express the dynamic child graph. Manager initialization registers the private scope's structural disposer first and its drain disposer afterward, so reverse unwind invokes the drain before releasing that scope; merely registering a cleanup effect on the same scope as later Agent handles would allow structural handle disposal to bypass child-first ordering. Each materialization registers its barrier participant and snapshots its exact live ancestry before starting the inner transaction, then remains tracked until it installs an Activation or fully rolls back. The Activation retains weak membership of that ancestry, so an intermediate Agent may leave the registry without hiding a still-live descendant from its host root. Each Activation installs one memoized disposal promise before cancellation or recursive callbacks, allowing scoped host shutdown, global manager unload, child release, and normal settlement to converge without double release. Cancellation propagates top-down before slow descendant cleanup; handle release remains child-first. Sibling branches drain independently; one disposal failure is recorded but does not prevent the manager from attempting the remaining selected handles, and the aggregate drain reports failure after all selected branches settle. Durable child Sessions survive this process-local teardown.
 
-### Deferred report delivery
+### Report delivery extension
 
-This version exposes no `report` tool and provides no child-to-parent content delivery or automatic parent wakeup. The durable child Session remains the source of the child's detailed output.
-
-A later proposal may add an ordinary model-facing `report(output)` tool that can be called zero or multiple times in one turn. Its delivery policy may distinguish quiet parent injection from waking the parent; recipient selection, acknowledgement, durability, and retry semantics are deferred with that tool. Adding report delivery does not require another Activation state or execution queue.
+The optional child-scoped `report(output)` tool was added later without changing Activation residency or adding another queue. It can be called zero or multiple times per turn, derives the live direct parent rather than accepting a recipient, and selects quiet injection or a waking parent follow-up through deployment config. The [report-tool Agent Note](2026-07-30-continuable-subagent-report-tool.md) owns its authority, acknowledgement, setup-contribution, and delivery contracts.
 
 ### Deferred steering
 
@@ -147,7 +145,7 @@ Session and descriptor persistence survive restart. Activation state, Agent inbo
 
 This version covers continuable in-process children and leaves one-shot delegation unchanged. Remote providers require a separate Activation handle with equivalent authenticated control and child-first quiescence contracts before they can support the same behavior.
 
-It adds no host-user continuation, subagent steering operation, report tool, child-to-parent content delivery, automatic parent wakeup, durable mailbox, cross-process lease, automatic replay of interrupted inbox work, team authority, workflow authority, public subagent cancellation operation, public residency query, new live-Activation or descendant limit, or runtime cache. Existing delegation-depth policy remains unchanged.
+It adds no host-user continuation, subagent steering operation, durable mailbox, cross-process lease, automatic replay of interrupted inbox work, team authority, workflow authority, public subagent cancellation operation, public residency query, new live-Activation or descendant limit, or runtime cache. Existing delegation-depth policy remains unchanged. Optional child-to-parent reporting is a later consumer of this lifecycle rather than part of the base continuable capability.
 
 ## Alternatives considered
 
@@ -159,7 +157,7 @@ It adds no host-user continuation, subagent steering operation, report tool, chi
 
 **Let the provider create, resume, or deliver through an Agent handle.** Initial providers own only `prepareContinuable()` and its detached creation-spec distinction: whether a child begins fresh or with a parent prefix. The manager must call `ctx.agents.create()` through its private activation-owner scope so that scope is a structural owner of every handle. A persisted in-process Session already contains the initial prefix and generic reconstruction descriptor, while delivery belongs to the Agent inbox. Giving providers any later handle, `SubagentRun`, or message ownership would preserve a seam with no shipped behavior to own.
 
-**Add report delivery now.** A repeatable model-facing tool is compatible with this lifecycle, but quiet versus waking delivery, recipient selection, acknowledgement, durability, and retry behavior are independent product choices. Deferring the tool keeps the first version focused on conversation admission and residency without constraining that later policy.
+**Make report delivery part of the base lifecycle.** Repeatable child-to-parent reporting is compatible with this lifecycle, but quiet versus waking delivery, acknowledgement, durability, and retry behavior are independent product choices. The later report package remains optional and consumes an explicit child-setup seam, so continuable residency does not silently grant a return channel.
 
 **Treat `SessionHeader.parentSession` as live ownership.** Durable lineage does not prove that the historical parent currently owns the child. Membership in the live parent's `ownedChildren` records the process-local relationship without changing durable provenance.
 
@@ -195,12 +193,13 @@ The implementation pins these behaviors:
 - Every continuation-managed parent Activation disposes only after all directly owned child Activations complete `AgentHandle` disposal; top-level Agents do not join the waiting graph.
 - Final Activation settlement awaits `ctx.sessions.flush(child.session)` as a best-effort barrier, logs rejection without interpreting listener participation as durability proof, then disposes the child handle and releases parent ownership so a flush failure cannot leak a `waiting` Activation.
 - Manager teardown closes admission globally; a host owning selected top-level Agents instead closes admission only below their exact identities until those roots leave the registry. Both track admitted materializations by exact ancestry, install one memoized disposal cutoff per selected visible Activation, propagate cancellation top-down, release handles child-first, await every selected branch despite individual failures, and only then dispose the corresponding top-level Agents or manager scope.
-- This version exposes no `report` tool, child-to-parent content delivery, or automatic parent wakeup.
+- The base lifecycle has no implicit report behavior; the optional report package contributes an explicit child-scoped tool through the setup seam.
 - Session logs reconstruct only messages that were actually written, with their admitted provenance; inbox-accepted but unlogged messages have no restart guarantee.
 - No continuable-subagent path creates or depends on a Task, `TaskId`, Task completion notice, Task cancellation, or intermediate result-bearing execution wrapper.
 - Unit coverage pins the `startContinuable()` inbox-acceptance return boundary, complete rollback for each pre-acceptance and lifecycle-publication failure, global and parent-scoped drain quiescence for materialization caught between Agent publication and Activation registration, sibling-forest isolation, exact ancestry after an intermediate Agent leaves the registry, provider-independent cold resume, final exact-parent reauthorization after cold-resume materialization, caller-signal and teardown ownership on both sides of acceptance, and the absence of automatic replay for accepted-but-unlogged messages.
-- Unit coverage pins the residency-only routing table, single-inbox ordering, `MessageId` correlation through inbox events, follow-up during an open turn, waiting wakeup, cold resume, ownership registration and release, child-first disposal, send-versus-dispose races, best-effort final flush with absent and failing listeners, and the absence of public subagent cancellation, steering, and report tools.
-- A keyless assembled-app snapshot covers parent delegation and follow-up queueing, the absence of subagent steering, report delivery, and automatic parent wakeup, retained waiting `AgentHandle`, and child-first disposal.
+- Unit coverage pins the residency-only routing table, single-inbox ordering, `MessageId` correlation through inbox events, follow-up during an open turn, waiting wakeup, cold resume, ownership registration and release, child-first disposal, send-versus-dispose races, best-effort final flush with absent and failing listeners, and the absence of public subagent cancellation and steering.
+- Report-package unit coverage separately pins child-only visibility, setup revocation, authority, delivery modes, stable message identity, and lifecycle races.
+- A keyless assembled-app snapshot covers parent delegation and follow-up queueing, the absence of subagent steering and implicit report delivery, retained waiting `AgentHandle`, and child-first disposal. A separate report snapshot covers the optional explicit return channel.
 
 ### Accepted costs
 
@@ -210,7 +209,7 @@ Retaining an Activation while descendants run consumes Agent resources proportio
 
 The process-local inbox and ownership graph do not coordinate two harness processes. Deployments allowing concurrent access to one persistence store still require a durable lease and mailbox protocol.
 
-Without report delivery, completing a child turn neither sends its content to nor wakes the historical parent. The output remains in the durable child Session until a caller inspects that transcript or submits another authorized turn. A later report tool may add quiet or waking delivery without changing the Activation lifecycle.
+Without the optional report package, completing a child turn neither sends its content to nor wakes the historical parent. With the package, only an explicit `report` call sends selected content; quiet delivery does not wake the parent, while waking delivery enqueues one later turn. In every case the detailed child output remains in its durable Session.
 
 Queueing every continuation message means a parent cannot correct an in-progress child turn immediately; the correction runs as the next turn. A later UI steering action may reduce that latency without changing follow-up ordering.