docs: rename core-data-structures/ to subsystems/

The folder is becoming the home of one-doc-per-subsystem pages (intro +
data structures + cordis services/events), so the name must describe the
whole contract, not just the type-vocabulary third of it. Mechanical
rename rebuilt on current master: every inbound Markdown link, generator
constant, website route, type-equiv manifest path, and spec expectation
moves together; the zh sides of the notes whose prose names the folder
are aligned (子系统) in the same change; touched bilingual pairs
re-recorded; translation-prompt snapshot re-recorded (its example embeds
development.md). Historical Agent Note slugs keep their dated
filenames.

docs/subsystems/goal.md

@@ -0,0 +1,145 @@
+# Same-session goals
+
+English | [中文](goal.zh.md)
+
+Types shared by the event-sourced goal domain and its policy consumers. The [goal-domain Agent Note](../../.agents/notes/implemented/feature/2026-07-19-persisted-same-session-goal-domain.md) owns the persistence and activation decisions; this page records the literal shapes from [`packages/goal/goal/src/types.ts`](../../packages/goal/goal/src/types.ts).
+
+## Identity and lifecycle
+
+`GoalId` is a [branded id](core.md#branded-ids). A caller mutates one exact revision through `GoalRef`; every accepted durable mutation increments the revision.
+
+```ts type-equiv
+/** Compare-and-set identity for one exact goal revision. */
+interface GoalRef {
+  /** Stable goal identity. */
+  readonly id: GoalId
+  /** Positive revision; every durable mutation increments it. */
+  readonly revision: number
+}
+```
+
+The durable phase answers what happened to the objective. Process-local activation separately answers whether a continuation consumer may start another round.
+
+```ts type-equiv
+/** Durable continuation phase. Activation is process-local and separate. */
+type GoalPhase =
+  | 'active'
+  | 'paused'
+  | 'blocked'
+  | 'complete'
+```
+
+Blocking is the single durable stopped-by-a-problem state. Its policy-owned reason carries a stable lower-kebab-case code for routing and a free-form explanation for humans and models.
+
+```ts type-equiv
+/** Machine-routable and human-readable explanation for a blocked goal. */
+interface GoalBlockReason {
+  /** Stable lower-kebab-case classification chosen by the blocking policy. */
+  readonly code: string
+  /** Non-empty explanation shown to humans and models. */
+  readonly message: string
+}
+```
+
+```ts type-equiv
+/** Full durable state written by every non-clear goal mutation. */
+interface GoalSnapshot extends GoalRef {
+  /** Human-requested completion objective. */
+  readonly objective: string
+  /** Durable lifecycle phase. */
+  readonly phase: GoalPhase
+  /** Present exactly while `phase` is `blocked`. */
+  readonly blockedReason?: GoalBlockReason
+  /** Total admitted goal-round cap. */
+  readonly maxGoalRounds: number
+}
+```
+
+```ts type-equiv
+/** Current goal projection, including values derived from the session log. */
+interface GoalView extends GoalSnapshot {
+  /** Highest admitted round number for this goal. */
+  readonly roundsStarted: number
+  /** Epoch milliseconds of the create mutation. */
+  readonly createdAt: number
+  /** Epoch milliseconds of the latest mutation. */
+  readonly updatedAt: number
+  /** Process-local continuation eligibility; never persisted. */
+  readonly activation: GoalActivation
+}
+```
+
+## Durable changes
+
+Every mutation is a durable `goal/change` session event whose payload is either a complete post-mutation snapshot or a clear tombstone. The strict fold and persisted projection derive lifecycle state only from these events; inbox mutations do not affect goal state.
+
+```ts type-equiv
+/** Full-snapshot goal mutation committed by a durable `goal/change` event. */
+interface GoalSnapshotChangeMeta {
+  readonly kind: 'goal/change'
+  readonly version: 1
+  readonly operation: Exclude<GoalOperation, 'clear'>
+  readonly goal: GoalSnapshot
+  readonly roundsStarted: number
+  readonly createdAt: number
+  readonly updatedAt: number
+}
+```
+
+```ts type-equiv
+/** Tombstone retained when the current goal is cleared. */
+interface GoalClearChangeMeta {
+  readonly kind: 'goal/change'
+  readonly version: 1
+  readonly operation: 'clear'
+  readonly cleared: GoalRef
+  readonly clearedAt: number
+}
+```
+
+A continuation consumer attributes each admitted user-message turn with a positive, sequential round number and the current revision; only these admitted `user/message` events advance `roundsStarted`. Replay rejects non-positive rounds, gaps, stale revisions, stopped phases, and cap overflow.
+
+```ts type-equiv
+/** Message attribution for admitted continuation rounds. */
+interface GoalMessageSource {
+  readonly kind: 'goal'
+  readonly goalId: GoalId
+  readonly revision: number
+  /** Positive admitted continuation round. */
+  readonly round: number
+}
+```
+
+## Requests and notifications
+
+Creation separates caller omission from the deployment choice, which `create()` resolves internally. An edit is a partial replacement whose runtime validator requires at least one field. Every mutation notification carries the accepted operation and exact revision; clear omits `goal`.
+
+```ts type-equiv
+/** Input whose omitted round cap is resolved by the service configuration. */
+interface CreateGoalRequest {
+  readonly objective: string
+  readonly maxGoalRounds?: number
+}
+```
+
+```ts type-equiv
+/** Fields changed by an edit; at least one must be present. */
+interface EditGoalRequest {
+  readonly objective?: string
+  readonly maxGoalRounds?: number
+}
+```
+
+```ts type-equiv
+/** Live notification after one durable goal mutation commits. */
+interface GoalChanged {
+  readonly operation: GoalOperation
+  readonly ref: GoalRef
+  /** Absent for a clear tombstone. */
+  readonly goal?: GoalView
+}
+```
+
+## Service behavior
+
+[`GoalService`](../../packages/goal/goal/src/index.ts) resolves creation defaults, folds strict replay from durable `goal/change` events, enforces exact-live-agent identity and compare-and-set mutations, and emits contained `goal/changed` notifications. The package [README](../../packages/goal/goal/README.md) owns the callable and model-visible contract.