feat(coder/modules/agentapi): add state persistence

[mafredri]

AgentAPI can save and restore conversation state across workspace restarts.
The base module exports env vars (AGENTAPI_STATE_FILE, AGENTAPI_SAVE_STATE,
AGENTAPI_LOAD_STATE, AGENTAPI_PID_FILE) that the binary reads directly.
No consumer module start scripts need changes.

New variables:

• enable_state_persistence (bool, default true)
• state_file_path (string, defaults to $HOME/<module_dir_name>/state.json)
• pid_file_path (string, defaults to $HOME/<module_dir_name>/agentapi.pid)

State persistence requires agentapi >= v0.12.0. A shared version_at_least
function in scripts/lib.sh gates both the env var exports in main.sh and
SIGUSR1 in the shutdown script. Old binaries get a warning and graceful
skip instead of breakage.

Shutdown script now performs a three-phase shutdown:

1. SIGUSR1 to trigger state save (gated on version + persistence enabled)
2. Log snapshot capture (existing behavior, now fault-tolerant via subshell)
3. SIGTERM for graceful termination with wait loop

Also bumps agentapi module version to 2.2.0 and claude-code to 4.7.6.

Closescoder/internal#1257
Refs coder/internal#1256
Refs #696

[DevelopmentCats]

LGTM aside from what has already been pointed out.

@35C4n0r You might have some better insight on this since agentapi.

[35C4n0r]

Code LGTM!
I'd test it once before approving.

[mafredri]

FYI I flipped enable_state_persistence to default false. The feature would be silently skipped anyway while emitting a confusing warning on every start. I think it's better if modules opt in when they bump (as claude-code does in #749).

[johnstcn]

LGTM, nice work!