[t3-code-sandboxes]

Stacked on #71.

Problem. In a normal T3 chat, when the agent wakes on its own (a background task or subagent finishing, a Monitor line, a scheduled task), the reply appears in the chat on every client. In a sandbox chat seen through the host (the phone, or a desktop not paired with the sandbox), it didn't. The bridge only relayed the sandbox run carrying the host's forwarded message, and after #68 it only reported the background roster. The agent woke on the sandbox, but its reply never reached the host's mirror, not even on the next turn.

Fix (bridge and host ACP adapter; orchestration unchanged).

• The bridge treats a sandbox run whose message nobody typed (createdBy !== "user", or a scheduledTaskId) as a wake. It only considers runs that started after the newest run a host turn followed, so no history is replayed. For each wake it sends a new ACP notification (SANDBOX_BRIDGE_WAKE_METHOD) with the sandbox's message id, text and notice, without sandbox-only ids.
• The sandbox flavor turns it into a provider continuation through the existing offerContinuationRun, which keeps one request pending and ignores notices during a running turn. The host message reuses the sandbox's message id, text and notice.
• The wake run's prompt carries the sandbox's message id, so the existing turnTargetOf attaches and relays it with the same TurnTracker as normal turns, starting at that message. A continuation whose message the sandbox doesn't have does nothing, and its text never reaches the sandbox.
• fix(sandbox): a sandbox chat stays Working while its sandbox thread works on #68's follow now keeps going until the next prompt or until the bridge process ends, because a task's end and the wake it causes arrive separately. That costs one subscription per live bridge, on perf(sandbox): sandbox chat turns reuse one connection and send less #66's shared compact connection, bounded by idle session release.
• Left as is:
  • A wake right after a user's Stop isn't shown until the next host turn, because the adapter blocks wakes after a Stop.
  • If a user's message waits on the sandbox behind a wake, the wake's remaining output shows in the user's turn.

Test plan

• bridge.test.ts: shows a run the sandbox starts itself as a run of the host's, once. It asks the host once with the cleaned notice, streams the reply, and dispatches nothing to the sandbox (fails on the base).
• AcpRegistryAdapterV2.test.ts: starts a run when the bridge reports one the sandbox began itself. A repeated notice gives one continuation, and the prompt carries the sandbox's message id (fails on the base).
• bridge.test.ts, AcpRegistryAdapterV2.test.ts and AcpAdapterV2.test.ts (206 tests), and typecheck of contracts, provider-acp, provider-acp-registry, sandbox-bridge and server pass. In check:changed, only the known base failures fail (remote-parent fixture, the tailscale host leak), both fixed in test: fix the tests that fail on the sandbox branch itself #69.

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