TMUX boundary refactor — move ~2,073 LOC from Advance to OCA (O1)

[JRedeker]

Summary

Advance contains a full tmux infrastructure layer (~2,073 LOC) that conflicts with OCA's session management. Move tmux execution to OCA; keep intent/decision logic in Advance.

Why

• Advance uses default tmux socket; OCA uses -L oca named socket → windows invisible to OCA session management
• Advance's openTmuxWindow ignores OCA's Pattern B per-project session topology
• Both implement mutex serialization independently
• ~1,500 LOC can be deleted from Advance after migration

Acceptance Criteria

• OCA adds oca session rename-window, oca terminal detect, oca session current
• Advance replaces openTmuxWindow() → calls oca session ensure-window
• Advance replaces rename-window → calls oca session rename-window
• ~1,500 LOC deleted from Advance
• Both test suites pass

Proposal

docs/proposals/2026-05-08-cross-repo-boundary-audit.md § O1 + § TMUX Refactor

Cross-repo

This is a cross-repo change. OCA adds CLI surface first (Phase 1), then Advance migrates (Phases 2–4).

WSJF Estimate

Value: 9 | TC: 7 | RROE: 8 | Effort: 8 | WSJF: 3.0