bug(sessions): restart kills healthy opencode terminal sessions that take longer than 30 s to become input-ready #772

Symptom

After an app restart every OpenCode Terminal pane comes back blank and, about 32 s later, flips to failed ("Timed out waiting for agent to become ready for input"); the process is gone. Waking the same pane manually afterwards works in 2–4 s. Owner's report: "opencode terminal resume is fucked up".

Evidence

Incidents journal ~/.config/agent-code/incidents/runs/2026-09-03T23-43-59-…/events.jsonl (app restart after app.prior_unclean_shutdown):

• 23:44:02.6 recover.request ×3 (caller agent-terminal-leaf.attach-retry, hasResumeId: true).
• 23:44:04.9 recover.spawned … lifecycle: "live", ready: false (providerStart 2–3 ms; ps shows opencode --session ses_… --auto, the correct CLI form on 1.18.27).
• 23:44:34.9 kill.request cause: "live-entry" + wake.result ok:false code:"start-failed" durationMs: 32283/32415/32447 for all three; no exit in between — the processes were alive.
• ~/.local/share/opencode/log/opencode.log has no run between 23:06 and 23:45:33: the three TUIs never reached their first log line inside 30 s (ten Claude sessions were rehydrating concurrently; opencode.db is 1.47 GB and every invocation opens it).
• Same session re-woken manually at 23:45:33 → ready: true in 1.7 s.

Mechanism

src/renderer/src/workspace/hook/actions/session.ts ensureSessionLive (~699-736): after session:recover returns disposition: 'spawned', ready: false, it runs waitForSessionInputReady with a hard-coded 30 s (~198-201, 703) and on timeout calls killSessionBackendIfOwned and marks the pane failed/start-failed (~734-773). For the terminal runtime "input ready" is merely first PTY byte + 250 ms (src/providers/opencode/runtime/opencodeTerminalSession.ts:130-146) — a boot-latency measurement, not a health signal — and on this machine TUI boot ranges from 0.5 s idle to >30 s during restart. AgentTerminalLeaf.tsx (~366-372) only retries its attach after the wake resolves, so the pane is also blank for the whole boot even when it succeeds.

Identity capture and the CLI resume form are correct (opencodeCliSessions.ts:97-118, opencodeTerminalSession.ts:112-123; workspace.json holds providerSessionId: "ses_…").

Expected

1. A readiness timeout must never kill a backend that has not exited: leave the pane started and not-ready (the existing "accepted cost" comment already argues this); keep the kill only for exited/failed. For providerRuntime === 'terminal' skip the readiness wait, like the adoptedLiveBackend short-circuit.
2. AgentTerminalLeaf retries the attach as soon as the recover RPC resolves (backend live), not after readiness, so the booting TUI is visible immediately.

Tests

• sessionRecovery.renderer.test.tsx: spawned terminal-runtime backend that never publishes ready → wake resolves ok, no kill, pane started; spawned non-terminal backend past the deadline but not exited → not killed.
• Leaf test: first attach null, recover resolves before readiness → attach retried and buffer replayed before ready.
• Deterministic repro: point setup.json.toolPaths.opencode at a wrapper that sleeps 35 s then execs opencode; restart with one OpenCode Terminal pane.

Related: deliverPromptText has a 15 s readiness cap (opencodeTerminalSession.ts:14, 206-227) that fails under the same load; rehydrate.ts:64 shares the fragile 30 s constant. Also a factor in the ~3-minute boot the owner reports.

Refs #596, #739.