v0.8.1 fix: make hub lifecycle safe in nested tmux

[minglong51]

Summary

• Reliable hub return: clilane hub now restores the invoking shell or outer c/cdev tmux pane when its popup closes.
• Generation-owned input: stale popup processes cannot detach a client, switch its session, or overwrite a newer switcher generation.
• Clear nesting behavior: recursive entry on the same CLI Lane tmux server is blocked with guidance, while valid outer-tmux nesting on another socket remains supported.
• Inert backing session: the hidden hub pane uses a non-interactive standby process instead of leaving a login shell behind.

Test Coverage

CODE PATHS                                      USER FLOWS
[+] Recursive hub entry                        [+] Start and reopen switcher
  ├── TESTED: outside tmux proceeds               ├── TESTED: normal shell launch
  ├── TESTED: same managed server is rejected     ├── TESTED: existing-task switch
  ├── TESTED: different outer socket proceeds     └── TESTED: new-session launch + retry
  └── GAP: malformed socket metadata fallback

[+] Popup ownership and cleanup                [+] Popup loss and replacement
  ├── TESTED: forced close clears owned state     ├── TESTED: forced close cleanup
  ├── TESTED: stale generation is a no-op         ├── TESTED: overlap keeps newest generation
  ├── TESTED: moved client is not detached        └── TESTED: nested popup returns to outer tmux
  ├── TESTED: raw and launch claims clean up
  └── GAP: defensive malformed-state branches

[+] Hub UI generation flow                     [+] Recursive invocation
  ├── TESTED: generation registration             ├── TESTED: same server blocked with guidance
  ├── TESTED: popup failure cleanup               └── TESTED: different server remains usable
  ├── TESTED: detach, switch, launch, retry
  └── GAP: invalid stale-at-entry guards

[+] Shell-free hub standby
  ├── TESTED: Python standby replaces shell
  ├── TESTED: existing hub reuse and reopen text
  └── GAP: non-TTY/EOF defensive branches

COVERAGE: 27/32 changed paths (84%) | USER FLOWS: 6/6 (100%)

PTY assertions: 56 → 108 (+52).

Pre-Landing Review

No issues found. Independent testing, maintainability, and concurrency reviews were clean.

Design Review

No frontend files changed; design review skipped.

Eval Results

No prompt-related files changed; evals skipped.

Scope Drift

Scope Check: CLEAN

Plan Completion

• Deterministic regressions cover popup loss, stale generations, same-server recursion, valid outer-tmux nesting, and standby behavior.
• Exact-generation cleanup and tagged-server recursion detection are implemented.
• New hub sessions use the non-interactive standby process.
• Fresh verification covers provider evidence, the hub PTY smoke suite, and all unit tests.

Completion: 4/4 done, with no deferred items.

Verification Results

The plan contained no separate manual-verification section. Automated verification is listed below.

Test plan

• 95 unit tests pass across profile, release, and provider-evidence suites.
• Real tmux PTY lifecycle smoke passes, including forced popup close and nested tmux return.
• Provider evidence check passes for all 24 cells.
• Python 3.10 syntax parse and git diff --check pass.

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