fix(subagent): inherit parent policy overrides in continuable children

A continuable background child (the default backgroundMode for both
delegation tools) never received the parent session's explicit
sandbox/approval overrides: materialization applied only child
composition, so a danger-full-access parent produced workspace-write
children whose every out-of-workspace operation raised an approval
prompt.

Move the one-shot driver's capture/append pair into the shared
child-agent module (captureDelegatedPolicyOverrides /
appendDelegatedPolicyOverrides) and call it from both paths:
startContinuable captures before its first await, only fresh
materialization appends the source-tagged events (after any fork seed),
and a cold resume replays the persisted delegation events instead of
re-capturing the parent.

Adds the continuable inheritance unit suite, the ACP snapshot scenario
subagent-continuable-inheritance (fails without the fix), the
continuable policy-inheritance Agent Note, and the seam-level README
contract, with bilingual counterparts.

Fixes #1692

packages/subagent/subagent/package.json

@@ -37,6 +37,8 @@
     "@deepseek-ai/dsh-brand": "^0.0.1",
     "@deepseek-ai/dsh-invariants": "^0.0.1",
     "@deepseek-ai/dsh-llm": "^0.0.1",
+    "@deepseek-ai/dsh-sandbox": "^0.0.1",
+    "@deepseek-ai/dsh-sandbox-policy": "^0.0.1",
     "@deepseek-ai/dsh-scope": "^0.0.1",
     "@deepseek-ai/dsh-session": "^0.0.1",
     "@deepseek-ai/dsh-session-persistence": "^0.0.1",
@@ -44,9 +46,16 @@
     "@deepseek-ai/dsh-session-projection-cache": "^0.0.1",
     "@deepseek-ai/dsh-tasks": "^0.0.1",
     "@deepseek-ai/dsh-tools": "^0.0.1",
+    "@deepseek-ai/dsh-user-approval": "^0.0.1",
     "cordis": "^4.0.0-rc.7"
   },
   "peerDependenciesMeta": {
+    "@deepseek-ai/dsh-sandbox": {
+      "optional": true
+    },
+    "@deepseek-ai/dsh-sandbox-policy": {
+      "optional": true
+    },
     "@deepseek-ai/dsh-session-persistence": {
       "optional": true
     },
@@ -58,6 +67,9 @@
     },
     "@deepseek-ai/dsh-tasks": {
       "optional": true
+    },
+    "@deepseek-ai/dsh-user-approval": {
+      "optional": true
     }
   },
   "devDependencies": {
@@ -65,6 +77,8 @@
     "@deepseek-ai/dsh-brand": "workspace:^",
     "@deepseek-ai/dsh-invariants": "workspace:^",
     "@deepseek-ai/dsh-llm": "workspace:^",
+    "@deepseek-ai/dsh-sandbox": "workspace:^",
+    "@deepseek-ai/dsh-sandbox-policy": "workspace:^",
     "@deepseek-ai/dsh-scope": "workspace:^",
     "@deepseek-ai/dsh-session": "workspace:^",
     "@deepseek-ai/dsh-session-persistence": "workspace:^",
@@ -74,6 +88,7 @@
     "@deepseek-ai/dsh-storage-domain": "workspace:^",
     "@deepseek-ai/dsh-tasks": "workspace:^",
     "@deepseek-ai/dsh-tools": "workspace:^",
+    "@deepseek-ai/dsh-user-approval": "workspace:^",
     "cordis": "^4.0.0-rc.7"
   }
 }