fix(sessions): verify session id in liveness check to prune ghost sessions

[tarkatronic]

Problem

Navi was showing more sessions than were actually running (e.g. 8 shown for 5 live Claudes). The liveness check was PID-only:

public var isAlive: Bool { pid > 0 && kill(pid, 0) == 0 }

kill(pid, 0) == 0 only asks whether some process holds that PID — not whether it's still the Claude session that created it. Two things defeated it:

1. Navi never updated a session's stored PID. When a session id is reused under a new process (a --resume, or /clear/compaction minting a new id on the same process), the stored PID drifts from reality.
2. A drifted PID stays "alive" via PID reuse. Once the original PID exits, the OS hands that number to another process, so kill(oldPid, 0) returns 0 and the dead session lingers as a ghost.

Confirmed concretely: a session id with hook activity but no live session file was still being counted because its recorded PID resolved to an unrelated live process.

Fix

• discoverSessions() now returns the set of session IDs whose own ~/.claude/sessions/<pid>.json points at a live PID — the authoritative identity-verified live set.
• Pruning keeps a session only when its own id is in that set (SessionInfo.isAlive(among:)), so a reused/drifted PID can no longer keep a dead session alive.
• Tracked sessions refresh their stored PID when a resume moves the id to a new process, keeping the PID-based display guard and terminal focus correct.
• Pruning is skipped entirely on a transient sessions-dir read error, so live sessions are never wiped.

Performance

Zero new filesystem work — this reuses the per-poll directory scan discoverSessions() already performs (1 readdir + a handful of small file reads). The only added cost is building a small Set<String> and one dictionary filter by set membership — microseconds. No process spawns; poll cadence unchanged.

Testing

• swift build clean
• swift test — all 95 tests pass, including 3 new isAlive(among:) cases (id in live set, ghost id with a live-but-wrong PID, empty set)

Version bumped 1.2.1 → 1.2.2 in .claude-plugin/plugin.json and Sources/NaviCore/Version.swift.

🤖 Generated with Claude Code