fix: handle --agent-name flag by resolving and reviving target session

[elecnix]

Problem

pi --agent-name solar-falcon-55 registered the flag but never acted on it. The --agent-name flag was registered via pi.registerFlag() but the extension never called pi.getFlag("agent-name") to process it. The flag was originally handled by a postinstall patch (patch-pi.mjs) that was later removed, leaving the flag orphaned.

This caused users to land in a new random agent instead of reviving the named one.

Fix

• resolveTargetSession() (new in daemon-client.ts): resolves a flag value to a session file, guarding against re-entry (skips when flag matches current agent name).
• session_start handler: checks pi.getFlag("agent-name"), and when it names a different agent registered in the daemon, spawns a new pi --session <file> process (mirroring the daemon's own resumeSession) and exits the current process.
• 5 new tests cover all edge cases: undefined flag, boolean flag, self-match, found, not-found.

How it works

pi --agent-name solar-falcon-55
  → session_start: polar-lemur-69 (new random name)
  → pi.getFlag("agent-name") → "solar-falcon-55" ≠ polar-lemur-69
  → query daemon for solar-falcon-55 → /path/to/session.jsonl
  → spawn pi --session /path/to/session.jsonl (detached)
  → exit current process
  → new pi loads solar-falcon-55's session ✓

— swift-badger-66