This folder catalogs the **data structures** of the DeepSeek Harness — what each core type represents, its literal shape, and where the full detail lives. It complements [architecture.md](../architecture.md), which describes *behavior* (the service map, the session/turn/step lifecycle, the event taxonomy); this page describes the *vocabulary* that behavior moves around.
## What counts as "core"
The harness is a microkernel: a tiny core plus many plugins. Most types belong to one plugin or one capability. A handful, though, are the **spine** — the language the agent loop and its events traffic in on *every* turn, no matter which optional plugins are loaded. Those are "core".
Precisely, a data structure is **core** if either:
1. it flows through the agent-loop spine — the loop holds it, derives it, streams it, or logs it on every turn (a `Message`, a `StreamChunk`, a `SessionEvent`, the `Agent` handle itself), independent of which plugins are present; **or**
2. it is the single headline type a plugin author writes against a pipeline — `ToolDefinition` (what every tool *is*).
Everything else is documented on a **sub-page**, not here. The rule that draws the line: *the type you write, hold, or receive is core; the machinery that types it, renders it, or persists it is a sub-page detail.* So `ToolDefinition` is core, but the `ValueSchemaSpec`/`ParameterSchemaSpec` inference machinery that types it, the `ToolCallView`/`ToolResultView` render-intent vocabulary that renders it, and the `SessionPersistence` seam that stores the event log are not — they live on the sub-pages below.
| [tools.md](tools.md) | `ToolDefinition` full fields, the schema DSL, `ToolExecution`/`ToolResult`, tool-presentation UI types, and the guarded execution pipeline |
| [subagent.md](subagent.md) | the subagent seam: the named-provider registry, `SubagentStartRequest`/`Result`/`Run`, the start-time-vs-runtime capability split |
> Type declarations and their JSDoc on these pages are source-equivalent and drift-checked by `pnpm run verify-type-equiv` (see [development.md](../development.md#documenting-types-verbatim-ts-type-equiv)). Ordinary blocks preserve complete declarations; `public-api` blocks preserve body-stripped public class declarations. Cordis services use the generated [service catalog](../cordis-catalog/services.md).
Almost every extensible sum type in the harness follows one shape: an interface keyed by a discriminant tag (the `…Map`), from which the union is derived with `keyof`. Plugins add variants by **declaration merging** — no edit to the owning package.
```ts ignore-check
// The pattern, schematically:
interface ThingMap {
'a': { kind: 'a'; /* … */ }
'b': { kind: 'b'; /* … */ }
}
type ThingKind = keyof ThingMap // 'a' | 'b'
type Thing = ThingMap[keyof ThingMap] // the discriminated union
// A plugin extends it without touching the source package:
Two large discriminated unions are the ones consumers `switch` over most: **`StreamChunk`** (the streaming protocol) and **`SessionEvent`** (the log entry). Per the repo convention, `switch` on the tag — don't chain `if`s — so each arm narrows and a typo'd tag fails to compile.
IDs that cross package boundaries are **branded** — structurally strings, but non-interchangeable at the type level (a `SessionId` cannot be passed where a `CallId` is expected). Construction goes through a per-type factory; comparison, logging, and JSON behave as ordinary strings.
The `Branded<B>` primitive lives in its own type-only package, [dsh-brand](../../packages/util/brand) (no runtime code, no harness-package dependency), so any package can brand the ids it owns without depending on an unrelated capability package.
The two core IDs are `CallId` (correlates a tool call with its result; dsh-llm) and `SessionId` (the shared live agent and durable session identity; dsh-session). Capability packages brand their own ids too, such as `TaskId` in [tasks.md](tasks.md).
The block interfaces (full fields in source): `TextBlock` (`text`), `ReasoningBlock` (thinking, distinct from visible text), `ToolCallBlock` (`id: CallId`, `name`, raw-JSON `arguments`), `ToolResultBlock` (`toolCallId`, nested `content: ContentBlock[]`, `isError?`). `ContentBlock = ContentBlockMap[ContentBlockType]`. The core set is limited to blocks every shipping path honors — multimodal content (images, audio, …) has no core block type; a feature that needs one adds it via the merge-extensible map together with the adapter/UI/compaction support that honors it.
A `Message` is one identified, immutable role/source/content value. Model-produced assistant messages carry provider/model ownership and optional adapter-private replay metadata in their source:
Adapters emit a raw **chunk** protocol; the loop logs the chunks (replay fidelity) while feeding the same chunks through a `BlockAssembler` to rebuild blocks and messages. `StreamChunk` is a closed discriminated union over `type` — `block-start`, `text-delta`, `reasoning-delta`, `tool-call-delta`, `block-end`, `usage`, `finish`.
The full union, the adapter contract (usage-before-finish, raw-JSON tool arguments, the two sanctioned error paths), and `BlockAssembler` live on **[llm-streaming.md](llm-streaming.md)**.
One model call is a fully-assembled `GenerateOptions`. The adapter answers with a raw `StreamChunk` stream; the consumer assembles it with `BlockAssembler` (see [llm-streaming.md](llm-streaming.md)).
Provider and model discovery uses small provider-neutral descriptors. A model catalog is advisory: routing still keys on a registered provider, and an adapter may accept unlisted model ids.
Adapter plugins additionally declare which routes *could* run through `registerConfigurableProviders()`, addressing each one's user-settings section, so configuration surfaces can offer dormant providers before any route registers.
```ts type-equiv
/**
* One provider route an adapter plugin can activate through configuration,
* whether or not the route is currently registered. Configuration surfaces
* merge this directory with `listProviders()` to offer every configurable
* provider alongside its live/dormant state.
*/
interface LlmConfigurableProvider {
/** Provider route key this entry activates when configured. */
provider: string
/** Human-readable provider name for configuration surfaces. */
displayName: string
/** User-settings namespace whose section configures this provider. */
settingsNs: string
/**
* Path from that namespace's section root to this provider's profile
* object; empty when the whole section is the profile.
Correctness-sensitive metadata is resolved separately from the advisory catalog and is owned by the adapter serving the exact route. Context capacity, adapter call defaults, and reasoning choices share one exact-model result so consumers do not repeat authoritative model resolution.
Reasoning effort is another exact-route capability. The core brands identifiers but does not enumerate their values; each adapter owns the ordered set, display names, and optional deployment default.
```ts type-equiv
/** Adapter-owned identifier for one model's selectable reasoning effort. */
type ReasoningEffortId = Branded<'ReasoningEffortId'>
```
```ts type-equiv
/** Display metadata for one adapter-owned reasoning effort. */
interface LlmReasoningEffortInfo {
/** Opaque stable value accepted by {@link GenerateOptions.reasoningEffort}. */
id: ReasoningEffortId
/** Human-readable effort name for selectors and diagnostics. */
name: string
/** Optional user-facing distinction from otherwise similar efforts. */
description?: string
}
```
```ts type-equiv
/** Selectable reasoning efforts for one exact provider/model route. */
interface LlmModelReasoningInfo {
/** Supported efforts in adapter-preferred display order. */
efforts: readonly LlmReasoningEffortInfo[]
/**
* Adapter-configured default materialized into requests when callers omit
* an effort. Absence preserves the provider's own default.
Why a model response stopped is a merge-extensible reason. Terminal provider failures carry the streaming contract's [`LlmFailure`](llm-streaming.md#llmfailure):
`FinishReason = FinishReasonMap[keyof FinishReasonMap]`. `TokenUsage` (per-call accounting with disjoint cache fields) is detailed on [llm-streaming.md](llm-streaming.md).
`GenerateOptions.tools` carries `ToolSchema` — the JSON-schema description of a tool, as sent to the model. It is declared in dsh-llm (not dsh-tools) precisely because it is part of the request the loop assembles every step:
The loop builds each request from logged state. `EpochHeader` records call config, adapter-default provenance, rendered prompt, and authoritative returned tool order (configured by `toolOrder`, or lexicographic when unset) through full `request/header` snapshots. Together with derived history, this makes the request reconstructable from the session log. See [session.md](session.md#the-request-header-event-requestheader) and the [reconstructability Agent Note](../../.agents/notes/implemented/architecture/2026-07-05-reconstructable-requests.md).
`agent/request` receives a frozen call-config seed and may return a replacement to switch provider, model, reasoning effort, or sampling. Before the waterfall, the loop removes values marked as adapter defaults so exact-model preparation materializes the selected route's current values; unmarked explicit settings remain in the proposal. After the waterfall, preparation rejects unsupported explicit effort ids without clamping and logs the effective config plus provenance under the turn signal. The prepared call keeps one adapter registration through dispatch. Requests reaching `llm/stream` are deep-frozen, so mutation throws, and carry a process-local loop identity so observers do not confuse separately logged frozen auxiliary calls with conversation requests.
On the wire, a loop-built request reads the `system` slot (the rendered prompt assembly) followed by the derived history — the boundary snapshot, whose tail is the newest `user/message` on a turn's first step and the previous step's tool results on later steps. The dev invariant recomputes exactly this equation against every loop-built request.
FIXME(call-config-shape): revisit which remaining fields are genuinely epoch-level for cache purposes (`model` and the model-owned reasoning effort are explicit; the sampling scalars sit here out of caution).
A `Session` is an **append-only log** of typed `SessionEvent`s — the single source of truth. The LLM message history is *derived* from the log (`deriveMessages()`), not stored separately. The event vocabulary derives from `SessionEventMap`:
The session event variants, `deriveMessages()` projection rules, `TurnEndReason` vocabulary, and execution-enclosure and standalone-event rules are on **[session.md](session.md)**. How the log is made durable — the `SessionPersistence` seam, JSONL/SQLite backends, the `session/flush` checkpoint, crash recovery, and `SessionHeader` — is on **[persistence.md](persistence.md)**.
`Agent` is the surface every plugin (UI, hooks, orchestrators) programs against. The concrete implementation is package-internal to dsh-agent-loop; nothing outside the loop depends on it.
Every pending occurrence is its `UserMessage`; `MessageId` is the sole identity. `Inbox.append`, `prepend`, `replace`, `remove`, `clear`, `splice`, and `claim` record normalized durable `agent/inbox/spliced` mutations and reject duplicate pending ids. `replace(messageId, newMessage)` and `remove(messageId)` locate the pending message across both lists; replacement may change identity and emits the old message as discarded followed by the new message as inserted. Ordinary removals and `clear()` are cancellations. `claim(target)` removes the proposed step batch — all `next-step` input plus, at a turn boundary, one `next-turn` message — through pure deletion splices without emitting discarded notifications, and the loop separately emits per-message claimed notifications. Whole-queue consumers such as UI projections reconstruct `nextTurn` and `nextStep` from the durable splices, while consumers following one message use the exact `agent/inbox/inserted`, `claimed`, and `discarded` notifications.
`Agent` is an interface over the public live-agent contract. Its unified `send` method exposes target and wakeup routing directly; `followup`, `steer`, and `inject` are fixed-preset aliases.
`AgentStatus` is `'idle' | 'running'`, and `SessionId` is branded. Disposal removes the agent from the registry and emits `agent/disposed`; it is not a terminal status value. `running` describes the driver-wide drain interval and may span consecutive queued turns; it does not prove a turn is still open. `followup()` returns no handle: its `MessageId` identifies durable inbox insertion, claim, and discard facts, not a later assistant output or turn ending. `whenIdle()` observes the whole agent, so callers may call a receipt-to-idle interval a run only when they explicitly own that interval ([decision](../../.agents/notes/implemented/architecture/2026-07-30-followup-enqueue-and-owned-runs.md)). `AgentOptions` is merge-extensible: core declares `provider?`, `model?`, and `maxTokens?` (dispatch requires provider and model after `agent/request`). When present, `maxTokens` must be a positive safe integer and caps every conversation-model request; omission allows the exact-model adapter default to materialize before the request header, or otherwise leaves provider behavior unchanged. Persona belongs to `dsh-system-prompt`: an agent-scoped `deployment:persona` may shadow the global default.
The cause is a TypeScript-enforced same-process input. An active cancellation holder copies it into the runtime-only `AbortSignal.reason`; a signal grants cooperating listeners no classification authority. Durable `turn/end` retains the coarse `{ kind: 'aborted' }` outcome; request provenance would require a separate durable event rather than overloading the terminal result.
The [event taxonomy](../architecture.md#event) owns the `agent/*` lifecycle, checkpoint, and waterfall contracts. Turn and step boundaries are durable session events rather than agent emits.
The process-local initiator carried by `ctx.agents` is the exact `Agent` above, not a separate frame or copied identity. Ambient presence is neither liveness proof nor authorization; the [initiator-scope decision](../../.agents/notes/implemented/architecture/2026-07-15-agent-initiator-scope.md) owns its lifetime and boundary rules.
Pre-step decisions use the same identified `UserMessage` shape as durable user-role input. The entered batch is authoritative and preserves every message's identity and provenance. Hook bridges map their native decision fields onto this typed result.
`agent/pre-step` receives the exclusive claimed batch and the proposed step's coordinates and cancellation signal. The initial proposal runs inside an open turn before any step; a tool continuation may submit an empty claimed batch between steps:
/** Coordinates and cancellation for a proposed step. */
interface PreStepContext {
/** Turn that will own the step. */
readonly turn: number
/** Step proposed by the loop. */
readonly step: number
/** Current turn cancellation signal. */
readonly signal: AbortSignal
}
```
It returns a `PreStepDecision`. Reject opens no step. Enter supplies the complete message batch appended after `step/start`; claimed messages omitted by the final decision remain removed, while input inserted after the claim stays pending:
```ts type-equiv
/** Whether and with which messages the loop enters a proposed step. */
`agent/request-error` runs after a failed model step closes and before its turn closes. Listeners can repair durable state or await policy work while the failed turn's signal is still live. A handling listener returns `{ kind: 'retry' }` without calling `next()`; the default `undefined` leaves the failure terminal.
```ts type-equiv
/** Action returned by a listener that owns model-request recovery. */
type RequestErrorAction = { kind: 'retry' } | undefined
`agent/pre-step` is the single serial boundary before request derivation. `agent/turn-stopping` runs when a turn has no tool or steering continuation, before one final steering drain.
The one pipeline-authoring type that is core: what every registered tool *is* — a model-facing `ToolSchema` plus an `execute` function and optional final-content and UI callbacks. A tool author rarely constructs it by hand (the `defineTool` DSL builds it with typed args), but it is the contract the registry holds and the loop dispatches through.
Its full fields, the `defineTool`/`ValueSchemaSpec`/`ParameterSchemaSpec` typed schema DSL, the `ToolExecution`/`ToolExecutionResult` waterfall shapes, and the tool-presentation UI vocabulary are on **[tools.md](tools.md)**.
