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.
Eric Traut