feat: three-prong session lifecycle fuse for opencode adapter

[c-h-]

Problem

opencode run (non-interactive mode) doesn't write session files to opencode's native storage directory. This means:

• Sessions launched via agentctl launch --matrix are invisible to agentctl list
• The events() generator never sees them start or stop
• No session.stopped lifecycle events are emitted to OrgLoop
• The supervisor never gets notified when coding agents finish

Discovered during ENG-8709 and ENG-8669 autonomous implementation runs: agents did real work (Kimi committed code, modified 5+ files) but died before pushing/opening PRs, and the supervisor was never woken.

Session meta files ARE written to ~/.agentctl/opencode-sessions/*.json with PIDs, but the discovery logic in list() and events() only enumerates from opencode's native storage (~/.local/share/opencode/storage/session/).

Design: Three-Prong Fuse

When agentctl launches an opencode session, register three signals. First to fire cancels the others (AbortController per session).

Signal 1: Wrapper Exit Hook (primary, immediate)

• Launch a thin wrapper script instead of opencode directly
• Wrapper runs opencode, captures exit code, writes it to a .exit file alongside the session meta
• On next poll cycle (≤15s), agentctl detects the exit file → emits session.stopped with exit code
• Gives us exit code for free, which PID poll alone can't provide

Signal 2: PID Death Poll (fallback, ≤15s latency)

• The events() generator polls kill(pid, 0) every ~15s for all tracked sessions
• Catches crashes, OOM kills, SIGKILL — anything the wrapper wouldn't survive
• Uses stored startTime from session meta to detect PID recycling
• If PID dies without an exit file: emit session.stopped with unknown exit code

Signal 3: Master Timeout (safety net, configurable)

• Configurable per-session, default 3 hours
• Emits session.timeout (distinct event type from session.stopped)
• Does NOT kill the process — the supervisor decides what to do
• Catches: zombie PIDs, PID recycled to another matching process, poll bugs

Fuse Pattern

launch → register { pid, exitFileWatcher, pollInterval, timeout, abortController }
any signal fires → emit event → controller.abort() → cancels the other two

Each session gets its own AbortController. Daemon tracks Map<sessionId, AbortController>.

Implementation Notes

• Wrapper collapses signals 1+2: exit file is the fast path, PID poll is the fallback
• Poll interval: 15s (cheap, kill(pid, 0) is ~0 cost)
• The list() method should also enumerate from the meta dir as a primary source, not just supplementary
• session.timeout should be a new event type in the lifecycle types
• Timeout is configurable via launch opts or agentctl config, not hardcoded

Current State

• Session meta files: ~/.agentctl/opencode-sessions/<uuid>.json (already written on launch ✅)
• PID stored with startTime for recycling detection ✅
• events() async generator exists but only watches opencode's native storage ❌
• No wrapper, no PID poll, no timeout ❌

Acceptance Criteria

• agentctl list -a shows sessions launched via --matrix / launch opencode
• session.stopped fires within 15s of opencode process exit
• session.timeout fires after configurable duration (default 3h)
• First signal cancels the other two (fuse pattern)
• Exit code captured when available (via wrapper)
• PID recycling detected and handled
• Existing claude-code/codex lifecycle behavior unchanged