fix(adapters): tell a failed window listing apart from an empty session (#525) - #751
fix(adapters): tell a failed window listing apart from an empty session (#525)#751dracic wants to merge 2 commits into
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`BaseTmuxBackend.list_window_ids` folded every non-zero `list-windows` exit
to `[]`, so a server erroring while its windows were alive read as an empty
session — a crash to the liveness probe, and a verified kill to the ctl-window
prune.
Answer `[]` only when stderr proves the session gone; raise `MultiplexerError`
otherwise. The proof wordings live in `BaseTmuxBackend._SESSION_GONE_STDERR`
("no server running", "can't find session"), matched case-insensitively, and a
leaf whose multiplexer words absence differently overrides the tuple.
Measured on the real binaries rather than the docs — tmux 3.4 and psmux 3.3.8
(66cf613), probed under an isolated registry so no live session was touched:
tmux list-windows -t =ghost rc 1 can't find session gone
tmux no server rc 1 no server running gone
psmux list-windows -t =ghost rc 1 no server running gone
psmux tampered key, windows ALIVE rc 1 Invalid session key unknowable
psmux wrong port, windows ALIVE rc 1 connection timed out unknowable
The last two are the defect made reproducible: identical exit code, session
demonstrably still serving its windows. They also rule out the simpler fixes —
a `has_session` round trip folds those same faults to False by its own
contract, and raising on every non-zero makes an ordinary vanished session
unverifiable, inventing a phantom survivor the prune re-reports forever.
Both psmux gone-wordings contain "no server running", so the leaf needs no
override; that is a measurement, not an omission.
All seven `_window_alive` call sites plus `prune_ctl_windows` already handle
`MultiplexerError` as "unknown, not dead" — the seam and its callers were
written for this, only the backend never raised. No engine change was needed.
`list_windows` and `session_options` get the same lens with the opposite
conclusion: they read metadata, not liveness, and their sentinel degrades
toward doing nothing, so `[]`/`{}` stays — but they now warn when the failure
proved nothing.
Known gaps:
- The full Windows suite last ran before the final fix: 7196 passed, 16 failed,
249 skipped, every failure in the known environmental categories (symlink
privilege x10, skill-sync drift x6). Post-fix verification covered the five
touched test files on both platforms: Windows 693 passed, Linux 718 passed,
no failures either side. The remainder of the Windows suite is unverified
against the final commit by choice; CI is the backstop.
- `uv run pyright` reports 7 pre-existing errors, all POSIX-only `os`
attributes in untouched `platform_util.py`. None in changed files.
- The metadata siblings keep their sentinel, so bmad-code-org#562 and bmad-code-org#538 stay open.
Closes bmad-code-org#525
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No actionable comments were generated in the recent review. 🎉 ℹ️ Recent review info⚙️ Run configurationConfiguration used: Organization UI Review profile: CHILL Plan: Team Run ID: 📒 Files selected for processing (2)
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Included review availability: Your plan provides up to 2 included reviews per hour; 0 remain after this review. WalkthroughThe tmux-family backend now uses stderr to distinguish a proven-gone session from an unproven listing failure. Liveness queries raise when the result is unknowable. Metadata queries retain sentinels and emit warnings. ChangesSession listing semantics
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The change distinguishes confirmed missing sessions from failed window queries so existing callers can preserve unknown states; no actionable merge-blocking risk remains after normal checks and review. Sequence Diagram(s)sequenceDiagram
participant Caller
participant BaseTmuxBackend
participant tmux_or_psmux
participant prune_ctl_windows
Caller->>BaseTmuxBackend: list_window_ids(session)
BaseTmuxBackend->>tmux_or_psmux: run list-windows
tmux_or_psmux-->>BaseTmuxBackend: windows or stderr failure
alt stderr proves session gone
BaseTmuxBackend-->>Caller: []
Caller->>prune_ctl_windows: classify candidates as removed
else failure is unproven
BaseTmuxBackend-->>Caller: MultiplexerError
Caller->>prune_ctl_windows: classify candidates as unverifiable
end
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🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Linked Issues checkExplanation The changes satisfy issue Full details: Docstring CoverageExplanation Docstring coverage is 58.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 48 functions across 7 files. (1 skipped: 1 unsupported.)
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Inline comments:
In `@CHANGELOG.md`:
- Around line 183-188: Condense the changelog entry to one terse, scannable,
imperative line summarizing the tmux-family window-listing behavior change:
distinguish confirmed missing sessions from other failures and raise on unproven
failures while retaining sentinel behavior where applicable.
In `@tests/test_psmux_backend.py`:
- Around line 209-210: Update the test documentation describing the
missing-binary behavior: state that list_windows makes one _run spawn attempt
and suppresses only the resulting warning, rather than returning silently
without spawning. Preserve the documented distinction from sessions already
proven gone, and do not change the tested behavior.
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CHANGELOG.mdsrc/bmad_loop/adapters/multiplexer.pysrc/bmad_loop/adapters/psmux_backend.pysrc/bmad_loop/adapters/tmux_base.pysrc/bmad_loop/tui/launch.pytests/test_multiplexer.pytests/test_psmux_backend.pytests/test_tui_launch.py
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…ment CodeRabbit, both accepted: - The CHANGELOG entry was a six-line narrative where AGENTS.md asks for terse, scannable and imperative. Condensed to one line; the reasoning lives in the commit and the PR, which is where it belongs. - `test_list_windows_does_not_probe_options_for_an_empty_listing` still said the base answers `[]` for a missing binary "silently, without spawning". That described the discarded pre-gate revision; the test's own assertion two dozen lines below proves one `list-windows` spawn happens and only the warning is suppressed. Left as written it invites restoring the early PATH return, which is exactly the regression the Linux gate caught on this branch.
1 participant
BaseTmuxBackend.list_window_idsfolded every non-zerolist-windowsexit to[], so a server erroring while its windows were alive read as an empty session — a crash to the liveness probe, and a verified kill to the ctl-window prune.The discrimination rule
Answer
[]only when stderr proves the session gone; raiseMultiplexerErrorotherwise. The proof wordings live inBaseTmuxBackend._SESSION_GONE_STDERR = ("no server running", "can't find session"), matched case-insensitively as substrings, and a leaf whose multiplexer words absence differently overrides the tuple.The
needs-designlabel was the point — the decision was which non-zero exits are proved-gone versus unknowable, and it is backend-specific. It was settled by measuring the real binaries, not by reading docs.The measurement
tmux 3.4 and psmux 3.3.8 (
66cf613), probed under an isolated registry so no live session was touched:tmux list-windows -t =ghostcan't find session: ghosttmux list-windows, no serverno server running on ...tmux -F #{bogus_field}psmux list-windows -t =ghostpsmux: no server running on session 'ghost'psmux, tampered.key, windows alivepsmux: Invalid session keypsmux, wrong.port, windows alivepsmux: connection timed outThe last two rows are the defect made reproducible: identical exit code, session demonstrably still serving its windows. Both psmux gone-wordings contain
no server running, and its client-side variant carriescan't find sessiontoo, so the leaf needs no override — a measurement, recorded at the call site, not an omission. A rejected-Fformat exits 0 on both binaries, so there is no such arm to discriminate.Rejected alternatives
A
has_sessionconfirmation round trip cannot arbitrate: that predicate folds every non-zero toFalseby its own documented contract, so it answers "gone" for exactly the auth and timeout faults this discrimination exists to catch. A tri-state return changes the seam's return type for every backend and caller to fix one branch. Raising on all non-zero makes an ordinary vanished session unverifiable, which invents a phantom survivor the prune re-reports forever — the same dishonest report from the other side.Blast radius
All seven
_window_alivecall sites inadapters/generic.pyplustui/launch.py:prune_ctl_windowsalready handleMultiplexerErroras "unknown, not dead". The seam contract and the callers were written for this; only the backend never raised. No engine change was needed — the fix lets the existing unknowable arms finally fire.list_windowsandsession_optionsget the same lens with the opposite conclusion: they read metadata, not liveness, and their sentinel degrades toward doing nothing, so[]/{}stays — but they now warn when the failure proved nothing.list_sessionsis deliberately untouched; its docstring already states that it conflates "no sessions" with "no multiplexer". #562 and #538 therefore stay open.Verification, and one caught regression
An earlier revision added a
shutil.whichpre-gate at the top oflist_windows. It short-circuited before the injected transport, so on a box without the binary the answer came fromPATHrather than from_run— green on Windows where psmux is installed, 15 failures on Linux where it is not. The pre-push Linux gate caught it. Thewhichcheck now sits inside the warning helper, where it gates only the warning, andlist_windows_answer_comes_from_run_not_from_pathpins the behaviour on both platforms.uv run pyright: 7 pre-existing errors, all POSIX-onlyosattributes in untouchedplatform_util.py. None in changed files.Closes #525
Summary by CodeRabbit
Bug Fixes
Documentation