Addresses #22833, #22245, #23067
## Why
`/goal` can keep synthesizing turns even when the next turn cannot make
meaningful progress. Hard usage exhaustion can replay failing turns, and
repeated permission or external-resource blockers can keep burning
tokens while waiting for user or system intervention.
## What changed
- Add resumable `blocked` and `usageLimited` goal states. As with
`paused`, goal continuation stops with these states.
- Move to `usageLimited` after usage-limit failures.
- Allow the built-in `update_goal` tool to set `blocked` only under
explicit repeated-impasse guidance. Updated goal continuation prompt to
specify that agent should use `blocked` only when it has made at least
three attempts to get past an impasse.
Most of the files touched by this PR are because of the small app server
protocol update.
## Validation
I manually reproduced a number of situations where an agent can run into
a true impasse and verified that it properly enters `blocked` state. I
then resumed and verified that it once again entered `blocked` state
several turns later if the impasse still exists.
I also manually reproduced the usage-limit condition by creating a
simulated responses API endpoint that returns 429 errors with the
appropriate error message. Verified that the goal runtime properly moves
the goal into `usageLimited` state and TUI UI updates appropriately.
Verified that `/goal resume` resumes (and immediately goes back into
`ussageLImited` state if appropriate).
## Follow-up PRs
Small changes will be needed to the GUI clients to properly handle the
two new states.
Adds the app-server v2 goal API on top of the persisted goal state from
PR 1.
## Why
Clients need a stable app-server surface for reading and controlling
materialized thread goals before the model tools and TUI can use them.
Goal changes also need to be observable by app-server clients, including
clients that resume an existing thread.
## What changed
- Added v2 `thread/goal/get`, `thread/goal/set`, and `thread/goal/clear`
RPCs for materialized threads.
- Added `thread/goal/updated` and `thread/goal/cleared` notifications so
clients can keep local goal state in sync.
- Added resume/snapshot wiring so reconnecting clients see the current
goal state for a thread.
- Added app-server handlers that reconcile persisted rollout state
before direct goal mutations.
- Updated the app-server README plus generated JSON and TypeScript
schema fixtures for the new API surface.
## Verification
- Added app-server v2 coverage for goal get/set/clear behavior,
notification emission, resume snapshots, and non-local thread-store
interactions.
