feat(sync): F2 — origin-gated conflict-detection

Closes the false-positive conflict-toast loop on history-replay. Conflict
notifications now fire only when the local field meta records origin='user'
AND the pull is not an initial hydration round.

Origin source-of-truth:
- shared-ai/field-meta.ts → originFromActor(actor) maps actor.kind onto
  the FieldOrigin enum: user→'user', ai→'agent', system+SYSTEM_MIGRATION
  →'migration', any other system source→'system'.
- Dexie creating/updating hooks call it once per write so every persisted
  field carries the right pipeline tag.
- repair-silent-twin + legacy-avatar wrap their writes in
  runAsAsync(makeSystemActor(SYSTEM_MIGRATION, ...)) so the hook stamps
  origin='migration'. Future replays of those rows from another device
  will not surface as conflicts.

applyServerChanges options:
- New ApplyServerChangesOptions { isInitialHydration?: boolean }.
- Push-response and pull-paged-loop callers compute it from the cursor
  state (`!oldestCursor` / `!cursor`). Pagination resets the flag after
  the first page.
- Conflict-trigger gates on `!options.isInitialHydration && localMeta[k]
  ?.origin === 'user'` in addition to the prior tests.

Tests (sync.test.ts):
- New: replay-burst (10 sequential server updates → 0 conflicts)
- New: agent-origin local write + server overwrite → 0 conflicts
- New: isInitialHydration suppresses everything → 0 conflicts
- New: real user edit + server overwrite → 1 conflict
- All 25 prior tests still pass.

29/29 vitest sync.test.ts cases green; svelte-check 0 errors over 7647
files.

Plan: docs/plans/sync-field-meta-overhaul.md F2 done-criteria met.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shared-ai/src/field-meta.ts

@@ -23,6 +23,7 @@
  */
 
 import type { Actor } from './actor';
+import { SYSTEM_MIGRATION } from './actor';
 
 /**
  * Pipeline that produced a given field value, from the perspective of
@@ -67,3 +68,23 @@ export function makeFieldMeta(at: string, actor: Actor, origin: FieldOrigin): Fi
 export function isUserOriginatedField(meta: FieldMeta | undefined): boolean {
 	return meta?.origin === 'user';
 }
+
+/**
+ * Map an actor onto the pipeline-origin we stamp at the Dexie hook.
+ *
+ * Rules:
+ *   - `kind: 'user'`   → `'user'`
+ *   - `kind: 'ai'`     → `'agent'`
+ *   - `kind: 'system'` with `principalId === SYSTEM_MIGRATION` → `'migration'`
+ *   - any other system source                                  → `'system'`
+ *
+ * Server-replay is set explicitly by `applyServerChanges`, never derived
+ * here — the local hook only sees writes the local code initiated.
+ */
+export function originFromActor(actor: Actor): FieldOrigin {
+	if (actor.kind === 'ai') return 'agent';
+	if (actor.kind === 'system') {
+		return actor.principalId === SYSTEM_MIGRATION ? 'migration' : 'system';
+	}
+	return 'user';
+}

packages/shared-ai/src/index.ts

@@ -38,7 +38,7 @@ export {
 } from './actor';
 
 export type { FieldMeta, FieldOrigin } from './field-meta';
-export { makeFieldMeta, isUserOriginatedField } from './field-meta';
+export { makeFieldMeta, isUserOriginatedField, originFromActor } from './field-meta';
 
 export type {
 	IterationPhase,