fix(agent-manager): detect agent at tmux pane PID

[codeaholicguy]

Summary

• evaluate the tmux pane PID with the same strict agent command matcher used for descendants
• preserve BFS descendant traversal and deepest-match selection
• add a regression test for agents that replace the pane shell

Root cause

TmuxManager.findAgentPid started its BFS at pane_pid but deliberately skipped command matching for that root node. When Claude or Codex replaces the tmux pane shell, the stable live agent is pane_pid and may have no matching descendant, so every managed-start poll returned null until the 15-second timeout killed the session.

Risk

Controlled and narrow: pane_pid is not accepted blindly. It must pass the existing per-agent strict command matcher, and the existing five stable PID polls remain unchanged. Descendant traversal and deepest-match behavior are preserved.

Regression proof

The new focused test expects a matching pane root PID. It failed before the fix with expected 100 / received null, passed with the fix, failed again when the old pane-root exclusion was temporarily restored, and passed again after restoring the fix.

Validation

• focused TmuxManager suite: 15 passed
• agent-manager suite: 480 passed
• agent-manager typecheck: passed
• agent-manager lint: passed
• agent-manager build: passed
• repository test suite: 901 passed
• repository build across 6 projects: passed
• commit hook repository lint: passed with pre-existing warnings only
• git diff --check: passed