Merge remote-tracking branch 'origin/master' into session-surface

Reconciles the session-surface work (surfaceOp/sourceEventSeqs provenance as
the sole derivation path) with master's worktree-subagent series (fork-seed
boundary + out-of-process subagent backends).

Semantic reconciliations beyond the textual auto-merge:
- SQLite SCHEMA_VERSION: both sides bumped 2->3. Merged to a single v3 carrying
  BOTH column families — master's seed_length on `sessions` and surface's
  source_event_seqs/surface_op on `events`. writeRow + both INSERT sites bind
  the full set; the schema doc lists all three added columns as the v2->v3 gap.
- agent-loop runStep request: master's `sessionId: session.id` and surface's
  per-append surfaceOp/sourceEventSeqs coexist (different regions).
- Fork seed + surface: a fork seeds the child from the parent's LIVE events,
  which now carry surfaceOp, so the child's surface rebuilds correctly. Verified
  end-to-end — the subagent-fork replay recalls the inherited "SAFFRON" codeword
  through the seeded prefix.
- Subagent snapshot fixtures (recorded pre-surface) re-enriched via KEYLESS
  deterministic replay: only surfaceOp/sourceEventSeqs added onto existing
  recorded lines (matched by seq), no recorded value changed. Not re-recorded
  against the live API.

Gates: typecheck, test (1112), test:snapshot (14), doc-sync, lint, build,
hygiene all green.

packages/session-persistence/session-persistence-sqlite/src/index.ts

@@ -241,19 +241,21 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
    */
   private writeRow(meta: SessionHeader): void {
     this.db.prepare(`
-      INSERT INTO sessions (id, version, created_at, cwd, parent_session)
-      VALUES (?, ?, ?, ?, ?)
+      INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length)
+      VALUES (?, ?, ?, ?, ?, ?)
       ON CONFLICT(id) DO UPDATE SET
         version = excluded.version,
         created_at = excluded.created_at,
         cwd = excluded.cwd,
-        parent_session = excluded.parent_session
+        parent_session = excluded.parent_session,
+        seed_length = excluded.seed_length
     `).run(
       meta.id,
       meta.version,
       meta.createdAt,
       meta.cwd ?? null,
       meta.parentSession ?? null,
+      meta.seedLength ?? null,
     )
   }
 }