Reload a thread's provider session from current config

[SawyerHood]

Human comments

What was wrong

Changing a provider's configuration (pi extensions, AGENTS.md, skills, plugin agent config, dynamic tools) needed a new thread; an idle thread's provider session could not be rebuilt in place.

What changed

• AgentRuntime.reloadThread → daemon thread.reload (stop with intent release, then resume the same providerThreadId, no timeline events) → POST /api/v1/threads/:id/reload → sdk.threads.experimental_reload → bb thread reload [id] [--self] → useReloadThread. Both composers treat an exact /reload as the operation, not model input.
• The server re-resolves environment, execution options, instructions, and tools at request time and refuses with 409 while the thread is active, has queued messages, or has a pending interaction; idle and error threads may reload.
• Wire change: HOST_DAEMON_PROTOCOL_VERSION 170 → 171 (new daemon command). Guide (bb guide threads), bb-cli skill, and docs/api_to_audit.md updated.

Prerequisite: #2444 (stack order; shares routes/threads/actions.ts context only).

How you verified

turbo run typecheck; turbo run test for @bb/server (public-thread-reload.test.ts), @bb/host-daemon (thread-dispatch.test.ts, dispatch/runtime-manager mocks), @bb/agent-runtime, @bb/cli, @bb/app (thread-detail, embedded-chat), @bb/host-daemon-contract, @bb/server-contract, @bb/sdk.

Fixes: none (upstream stack split).

AGENT GENERATED