feat(goal): add persisted same-session goal domain

docs/core-data-structures/goal.md

@@ -0,0 +1,139 @@
+# Same-session goals
+
+Types shared by the event-sourced goal domain and its policy consumers. The [goal-domain RFC](../rfc/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'
+  | 'usage-limited'
+  | 'budget-limited'
+  | 'complete'
+```
+
+```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
+  /** 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 `context/message` whose metadata is either a complete snapshot or a clear tombstone. The version, metadata, goal source, raw envelope, and rendered content form one replay invariant.
+
+```ts type-equiv
+/** Full-snapshot goal mutation retained in a model-visible context 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
+}
+```
+
+Goal state changes use round `0`. A continuation consumer attributes each admitted user-message turn with a positive, sequential round number and the current revision; replay rejects gaps, stale revisions, stopped phases, and cap overflow.
+
+```ts type-equiv
+/** Message attribution for durable goal state and continuation rounds. */
+interface GoalMessageSource {
+  readonly kind: 'goal'
+  readonly goalId: GoalId
+  readonly revision: number
+  /** Zero for state changes; positive for admitted continuation rounds. */
+  readonly round: number
+}
+```
+
+## Requests and notifications
+
+Creation separates caller omission from the resolved deployment choice. 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
+/** Validated create input with every deployment default materialized. */
+interface CreateGoalSpec {
+  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 goal mutation has been accepted for logging. */
+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, enforces exact-live-agent identity and compare-and-set mutations, overlays deferred injections, and emits contained `goal/changed` notifications. The package [README](../../packages/goal/goal/README.md) owns the callable and model-visible contract.