subagent: carry inherited policy overrides in the child session header

Review fix (ds-review-bot critical #2 on #623): the first-turn event stamp
had a durability hole no turn anchoring can close — an idle SessionStart-
style injection persists a complete one-shot turn before any prompt turn
opens, so a crash in that window left a resumable-looking child with no
inherited policy, falling back to a possibly wider deployment default.

The captured overrides now ride the child's creation meta into its
immutable SessionHeader (sandboxMode/approvalPolicy, neutral strings at the
session boundary — the delegationDepth precedent), durable from the moment
the session exists: no listener ordering can starve the baseline and no
crash window can lose it. overrideOf(session) on both policy services
resolves fold(events past header.seedLength) ?? header baseline, validating
against the closed vocabulary on read; stampOverride and the prompt-submit
listener machinery are deleted. The header field rides both persistence
backends (JSONL header line; SQLite sessions columns, SCHEMA_VERSION 11 —
pre-release, no migration). pty-local reads through overrideOf so PTY
spawns see the baseline too.

Red-first: header-durability-before-any-turn test (the injection crash
window shape), baseline/seed-boundary/closed-vocabulary contract tests in
both service suites; the real-wall suite (race, veto, fork stale-seed,
grandchild) re-anchored on header assertions and green. The Agent Note's
Alternatives now records the superseded event-stamping iteration with the
review evidence; bilingual docs updated.

packages/pty/pty-local/src/index.ts

@@ -9,10 +9,12 @@ import * as nodePty from 'node-pty'
 import type { IPtyForkOptions } from 'node-pty'
 import type { Agent } from '@deepseek-ai/dsh-agent'
 import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
+// Type-only: the `ctx.sandboxPolicy` Context merge and the `sandbox/mode`
+// SessionEventMap merge; the service itself arrives via `inject`.
+import type {} from '@deepseek-ai/dsh-sandbox-policy'
 import { PtyBackendCleanupError } from '@deepseek-ai/dsh-pty'
 import type { PtyBackend, PtyBackendSpawnSpec } from '@deepseek-ai/dsh-pty'
 import type { SandboxMode } from '@deepseek-ai/dsh-sandbox'
-import { effectiveSandboxMode } from '@deepseek-ai/dsh-sandbox-policy'
 import { type Config, type ResolvedConfig, validateConfig } from './config.ts'
 import { createProcessInspector } from './process-inspector.ts'
 import type { ProcessInspector } from './process-inspector.ts'
@@ -47,7 +49,7 @@ function ensureSandboxModeFence(ctx: Context, owner: Agent): void {
     if (eventName !== 'session/event') return
     const [session, event] = args as [Session, SessionEvent]
     if (session !== owner.session || event.type !== 'sandbox/mode') return
-    const currentMode = effectiveSandboxMode(session.events) ?? state.sandboxPolicy.defaultMode
+    const currentMode = state.sandboxPolicy.overrideOf(session) ?? state.sandboxPolicy.defaultMode
     if (event.data.mode === currentMode || !state.pty.hasOwnerActivity(owner)) return
     throw new Error(
       `cannot change sandbox mode from "${currentMode}" to "${event.data.mode}" while persistent terminal sessions are open or being created; wait for creation to settle and close them first`,
@@ -76,7 +78,7 @@ function childEnvironment(spec: PtyBackendSpawnSpec): NodeJS.ProcessEnv {
 
 function spawnArgv(ctx: Context, config: ResolvedConfig, spec: PtyBackendSpawnSpec): string[] {
   const argv = [config.shellPath, ...config.shellArgs]
-  const mode: SandboxMode = effectiveSandboxMode(spec.owner.session.events) ?? ctx.sandboxPolicy.defaultMode
+  const mode: SandboxMode = ctx.sandboxPolicy.overrideOf(spec.owner.session) ?? ctx.sandboxPolicy.defaultMode
   if (mode === 'danger-full-access') return argv
   return ctx.sandbox.confine(argv, {
     mode: mode,