Pane(fix[wait_for_text]): waits for new output, joins wrapped lines, prefers wait-for-channel for completion#47
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Pane(fix[wait_for_text]): waits for new output, joins wrapped lines, prefers wait-for-channel for completion#47tony wants to merge 22 commits into
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…onger matches (#45) why: wait_for_text returned found=True on the first poll whenever the pattern was already present in the pane when the call began, so agents using it to synchronise on command output saw the wrong result. The sibling wait_for_content_change already snapshots a baseline; wait_for_text now mirrors that pattern. what: - Snapshot (history_size, cursor_y) at entry; compute baseline_abs as the absolute grid index. Each poll re-reads history_size and captures from baseline_abs - hs_now + 1 onward, so the matched region tracks the pane's grid even as content scrolls into history. - Add _read_grid_position and _read_history_size helpers that expand the corresponding tmux format strings via display-message. - Drop content_start / content_end parameters; the baseline anchor supersedes them. Pre-alpha API contract makes this a clean drop. - Rewrite the docstring around the new "wait for new appearance" semantics, cross-reference search_panes for synchronous matches, and document edge cases (scrollback truncation, reverse-index sequences, clear/reset).
…#45) why: The baseline-anchor fix changes the user-visible contract for wait_for_text: a pattern already in the pane before the call must now return found=False, not the stale match the old code produced. The test suite needs to encode that contract so a future regression lands red. what: - Restructure WAIT_FOR_TEXT_FIXTURES with separate pre_command and during_command fields so fixtures can model "pattern was already on screen when wait_for_text started." - Add stale_scrollback_does_not_match: emit the pattern before wait_for_text starts and assert found=False on timeout. - Add matches_new_output_after_baseline: start the wait task, sleep, emit the marker via send_keys, assert found=True. Covers the positive path the baseline anchor was designed for.
why: The libtmux 0.56 bump merged on trunk ships Pane.display_message
as a typed wrapper around display-message, and every other tool
module in this package adopted it. The two helpers introduced for
baseline anchoring (_read_grid_position, _read_history_size)
reached back to raw pane.cmd("display-message", ...) instead.
Bringing them in line keeps the codebase consistent with the
same release-notes entry that markets the wrapper migration.
what:
- _read_grid_position and _read_history_size call
pane.display_message(fmt, get_text=True) directly; the parse logic
and empty-output fallback are unchanged.
- Rename the local "result" binding to "stdout" to match the call
surface used in meta.py.
why: capture-pane -S clips a below-visible start back to the bottom
visible row (cmd-capture-pane.c, in every tmux release we
support). When the cursor sits at the last visible row at entry,
start_line = cy0 + 1 lands below the pane and tmux returns the
bottom row's content. Stale text on that row — a fresh shell
prompt, a printed marker — matches the pattern instantly, before
any new output has appeared. The baseline-anchor fix that
motivated this branch did not close this corner: the math is
correct, but it assumed an empty capture result when start_line
pointed below the visible region.
what:
- Add _read_pane_height alongside _read_history_size. Read pane_height
once at entry; the bottom-row clip fires on entry-state, and a
per-tick read costs another tmux round-trip without changing
anything for the common case.
- Before each capture, short-circuit lines to [] when
start_line >= pane_height. Route through the existing deadline /
sleep tail so the loop honours the timeout instead of tight-
spinning.
- tests/test_pane_tools.py: regression for #45. Respawn the pane with
a sh -c that pre-fills, prints the marker without a trailing
newline, and sleeps — freezing hsize and cursor_y for the wait
window so the guard's first-tick contract is what's actually
tested.
…dget
why: start_time was captured after the initial _read_grid_position
and _read_pane_height calls, so a stalled tmux server could
block the tool for an arbitrary period before the user-supplied
timeout deadline even started. libtmux's tmux_cmd uses
Popen.communicate() without a subprocess timeout, so the worst
case is real, not theoretical: a server-side stall on the first
display-message leaks past the wall-clock budget the caller
asked for.
what:
- Move start_time and deadline to the start of the resolved-pane
block, before the baseline and pane-height reads. Same total work,
no new branches; only the budget accounting changes.
why: Three parameter values turn the wait loop into a footgun rather
than a wait primitive:
- ``pattern=""`` — ``re.compile('')`` matches the zero-width
position of every line, so the first poll returns
``found=True`` against whatever was already in the pane.
- ``interval=0`` — ``asyncio.sleep(0)`` yields the event loop
without idling, so the loop fires tmux subprocesses as fast
as the scheduler hands them out (a self-inflicted server-
side DoS).
- ``timeout<=0`` — the loop body runs one probe before the
deadline check, so a non-positive timeout silently turns
"wait" into "synchronous probe" without saying so.
Each is rejected at function entry so the failure surfaces as
an explicit ``ToolError`` instead of corrupting the contract.
what:
- Inline parameter checks before the regex compile in wait_for_text;
raise ToolError with the offending value in the message.
- tests/test_pane_tools.py: one test per rejection, asserting the
matching ToolError message.
why: The baseline-anchor mechanism assumes the pane's process and
grid stay coherent for the duration of the wait. Two events
break that assumption silently:
- respawn-pane mid-wait. screen_reinit (screen.c) resets cy to 0
but preserves hsize, so the absolute anchor keeps pointing at
the old process's grid — the new process's output ends up at
rows the capture skips, and the wait times out as if nothing
arrived.
- pane death. With remain-on-exit set, tmux keeps the pane alive
after its child exits and #{pane_dead} flips to 1. Without
detection, the loop just keeps polling a stale frozen grid
until the deadline.
Both cases now surface as explicit ToolErrors so callers can
react instead of timing out in the dark.
what:
- Replace _read_grid_position, _read_history_size, and
_read_pane_height with a single _PaneState NamedTuple read via one
display-message round-trip. Per-tick subprocess count drops from
three reads (entry + per-tick history + per-tick we'd need height)
to two (state + capture) without losing any fields.
- Capture pane_pid at entry; each tick checks pane_dead first and
then verifies pane_pid is unchanged. Either condition raises
ToolError naming the affected pane and the transition.
- tests/test_pane_tools.py: regression for respawn (asyncio.gather
pattern: start wait_task, respawn after 0.1s, expect ToolError)
and for pane death (set remain-on-exit, respawn into ``true``,
poll #{pane_dead}, expect ToolError).
…me-row blind spot
why: Two parts of the wait_for_text docstring oversold the
baseline-anchor model:
- The reverse-index note claimed ``\eM`` "rewrites history
below the baseline." It does not. screen_write_reverseindex
(screen-write.c) scrolls the visible region within
[rupper, rlower] or decrements cy. ``hsize`` is never
touched. A maintainer reading the tmux source to verify a
related claim would lose trust in the docstring.
- The "What 'new' means" block sells the tool as observing
NEW text without saying that in-place updates to the entry
cursor row (carriage-return rewrites, progress spinners,
single-line status updates) are excluded by design. Users
wiring this against TUIs that update in place see a silent
timeout.
what:
- Rewrite the reverse-index note around the real hazard — in-place
repaints below the baseline — and cite screen-write.c for the
visible-region scroll behaviour rather than asserting history is
rewritten.
- Add a paragraph under "What 'new' means" that explicitly
disclaims same-row rewrites and points readers at
wait_for_content_change for the in-place case.
…md format
why: The prior CHANGES entries on this branch carried commit-message
shape (why: / what: bodies, mechanism-heavy bullets) into a
changelog that AGENTS.md specifies as user-vocabulary prose
under Bold subheadings. Three CHANGES commits were dropped from
the branch via rebase; this single commit replaces them with
prose entries in the project's actual changelog format.
what:
- Breaking changes: parameter drop with before/after migration block.
- Fixes: one prose paragraph covering the baseline-anchor behaviour
change (stale-scrollback fix, bottom-row clip handling,
death/respawn surfacing) under a single user-vocabulary subheading.
- Fixes: one prose paragraph covering input validation.
- Section ordering: Breaking changes / Dependencies / Fixes, per
AGENTS.md line 420.
…'t match the implementation
why: Two comments in tests/test_pane_tools.py — the WaitForTextFixture
docstring and the docstring on
test_wait_for_text_matches_new_output_after_baseline — describe
the positive-path coordination as using asyncio.gather. The
implementation actually uses asyncio.create_task + a sequenced
await on the emit coroutine, because gather would schedule both
coroutines concurrently and lose the start-baseline-then-emit
ordering the test relies on. A future maintainer following the
comments would either rewrite the test incorrectly or doubt the
existing shape.
what:
- WaitForTextFixture pre_command docstring: replace the
asyncio.gather mention with asyncio.create_task plus a sequenced
await.
- test_wait_for_text_matches_new_output_after_baseline docstring:
describe the actual create_task + sequenced-await mechanism and
note explicitly that asyncio.gather is unsuitable here because it
loses the ordering guarantee.
…t precedent
why: The _stale_settled helper inside the wait_for_text parametrized
test waited 2 seconds for (history_size, cursor_y) to stabilise
across two consecutive polls. Every other settle-loop in this
file (_pane_dead, _ready, _bottom_row_ready) uses a 5-second
budget for similar tmux-state stability under shell activity.
The 2-second outlier risked flaking on CI nodes whose zsh
async-prompt hooks keep firing for longer than the budget,
missing the two-consecutive-identical-reads window that
signals settlement.
what:
- retry_until(_stale_settled, 2, raises=True) becomes
retry_until(_stale_settled, 5, raises=True). Happy-path wall-clock
is unaffected (the predicate returns True as soon as state
stabilises, usually within milliseconds); only the failure-mode
budget widens.
…nchor stays sound Adds a rollover guard inside the poll loop: when ``state.history_size < entry.history_size`` (grid_collect_history fired, clear-history ran, or the session's history-limit option was shrunk mid-wait), the absolute baseline ``hs0 + cy0`` is no longer recoverable. There is no server-side way to disambiguate "trimmed" from "still anchored", so surface the lost anchor as ToolError with a steer toward wait_for_channel for deterministic synchronization. Also fixes the stale ``pane_height`` reference in the bottom-row clip guard — it was captured once at entry and never refreshed, so a pane resize mid-wait left the guard keyed to a stale height. Compare against ``state.pane_height`` re-read each tick so the guard tracks the live visible region. Refs tmux grid.c grid_collect_history; verified against tmux master HEAD.
Passes ``join_wrapped=True`` (tmux ``-J``) to ``Pane.capture_pane`` so a pattern that crosses the pane's visual wrap is matched against the joined logical line. Without this, long error strings like "Build failed: module not found" got split across two rows by tmux and a naive ``re.search`` against each row in isolation never matched. The returned ``matched_lines`` entry for a wrap-crossing hit is the joined line and can therefore be longer than ``pane_width``; documented in the Notes section so agents that bound output understand the implication.
…nistic primitive Re-frames the wait family so agents pick the cheaper, race-free option first. Three coordinated doc edits: * ``send_keys`` docstring now forks the post-send choice into deterministic (``wait_for_channel`` + ``tmux wait-for -S``), pattern-match (``wait_for_text`` for output the agent doesn't control), and any-change (``wait_for_content_change``). * Server ``_INSTR_WAIT_NOT_POLL`` system instruction names ``wait_for_channel`` first; the 2 KB instruction budget is preserved by tightening the supporting prose. * ``wait_for_text`` docstring gains a ``When NOT to use this`` section that names the sequential-send_keys race and steers callers to the channel pattern with a pointer at the ``run_and_wait`` recipe. Tests: - ``test_base_instructions_prefer_wait_over_poll`` now requires ``wait_for_channel`` to appear in the system instructions and to be named before the fallbacks. - ``test_send_keys_docstring_cross_links_wait_for_channel`` is a cheap regression against future docstring drift.
The Phase 1 rollover predicate (``state.history_size < entry.history_size``) fires correctly on real row eviction — ``grid_collect_history`` trim, ``clear-history``, ``set-option history-limit <smaller>`` on tmux master — but ALSO fires on resize-grow when ``hscrolled > 0``. tmux's ``screen_resize_y`` (screen.c:451-465) decrements ``gd->hsize`` on a vertical grow by pulling rows from history back into the visible region. The rows are not freed; only the history/visible-region partition shifts and absolute indices stay valid. The Phase 1 predicate raised a spurious ``ToolError`` in that case. Trim and resize-grow are distinguished by ``pane_height``: trim leaves it unchanged, resize-grow increases it. Adding ``state.pane_height <= entry.pane_height`` as a conjunct makes the predicate the actual signature of row eviction, exempting resize-grow. Also walks back two over-broad claims that shipped with Phase 1: the "monotonically non-decreasing" framing in CHANGES (resize-grow proves it is not monotone) and the parenthetical about "shrinking history-limit mid-wait" — that retroactive-trim path requires tmux commit 195a9cf which is not in any tagged release as of tmux 3.6a. Adds test_wait_for_text_survives_resize_grow_with_scrolled_history.
… guard catches a subset A 2 ms high-frequency repro over ~3000 hsize samples showed the rollover guard's strict-inequality predicate (state.history_size < entry.history_size) never observes a dip during real history-limit overflow: tmux's grid_collect_history trims (~10% of hlimit) then immediately scrolls new lines back, so sampled hsize stays clamped near the cap. The predicate only fires when entry.history_size happened to land exactly at hlimit (environment luck). All earlier claims that "wait_for_text raises on history rollover" were therefore over-broad. Walk back the contract: * Docstring's "Scrollback rollover raises" Note now says "rollover detection is partial" and enumerates what is and isn't caught (clear-history yes; retroactive history-limit shrink on tmux >= 3.7 yes; grid_collect_history trim during continuous output NO). Points to the upcoming risk-band warning and to wait_for_channel for deterministic synchronization. * ToolError message changes from "history rolled over during wait" to "history shrank below entry baseline" -- describes what we actually detected (a shrink), not what we assumed (a rollover). * CHANGES breaking-change entry: same walk-back; references the new ### Fixes warning entry and the tracking issue filed in libtmux. * test_wait_for_text_raises_on_history_rollover renamed to test_wait_for_text_raises_when_history_is_cleared, since that is the path it actually exercises. Docstring trimmed to describe the test mechanism, with no dev-history narrative. * Same dev-history narrative removed from test_wait_for_text_survives_resize_grow_with_scrolled_history (same anti-pattern, same project guidance about not referencing the task or fix history in code comments). No behavior change beyond the message text and test rename. Phase 7 follow-up adds the risk-band warning predicate that catches what this guard does not.
… band The strict-shrink rollover guard misses grid_collect_history trim during continuous output: tmux trims ~10% of history-limit then immediately scrolls a line back, so sampled hsize stays clamped at the cap and the predicate state.history_size < entry.history_size never fires. A 2 ms high-frequency probe across ~3000 samples confirmed there is no sub-poll window where hsize dips below entry once entry was sub-cap. Emit a one-shot ctx.warning when sampled state enters the trim-risk band (top 10% of history-limit) AND the pane has advanced since the wait's baseline. MCP clients subscribed to notifications/message see "correctness is best-effort here. For deterministic synchronization use wait_for_channel." and can decide whether to keep waiting, retry, or switch primitives. Warning is one-shot per call so we don't spam. Adds history_limit: int to _PaneState; the field is read in the same display-message round-trip as the other per-tick fields, so the loop still costs two subprocesses per tick (state + capture). No CHANGES update in this commit -- the consolidated wait-for-text CHANGES entry will land in a later commit per the Narrative Bleed doctrine (no published-release user saw "no warning" to be "fixed"; this warning is just part of the new contract).
… output Adds the test the rollover claim should have had from the start. Earlier test_wait_for_text_raises_when_history_is_cleared exercises clear-history only -- not the grid_collect_history trim that fires during bursty output. This new test covers the actual real-rollover path. Shape: set history-limit=50 globally, split a fresh pane that inherits the small limit, attach a stub Context that records ctx.warning calls, start wait_for_text against a never-appearing pattern, burst 200 echo lines through the pane. tmux's grid_collect_history fires repeatedly, sampled history_size enters the risk band (>= 45), and the wait emits the one-shot trim-risk-band warning. The wait's found / timed_out result is intentionally not asserted -- the contract is best-effort once polling enters the risk band, so pinning a specific result would be over-specifying what tmux's grid model can't actually guarantee. The test pins the warning contract (what the tool guarantees) only.
…t for a published-release reader CHANGES walk-back and Phase 5 "spurious resize-grow" entries described intra-branch transitions a 0.1.0a6 user never saw. Consolidate the wait-for-text section into entries that describe only what the published release reader gets: * Breaking changes: one entry under "waits for new output, not stale scrollback" covers the #45 fix (real published bug), the new baseline-loss ToolErrors, the resize-grow exemption, the trim-risk-band warning, and the wait_for_channel cross-link. Reader needs zero branch context. * Fixes: keep the wrapped-line match and footgun-rejection entries (both real published bugs). Drop the "no longer raises spuriously on resize-grow" entry (phantom fix: 0.1.0a6 had no rollover guard to raise, spuriously or otherwise). The duplicate "waits for new output" Fixes entry is also dropped -- the consolidated Breaking changes entry covers it. Docstring Notes section in wait.py scrubbed of the tmux-commit-SHA citation and the forward-looking libtmux tracking-issue cross-reference. The tracking issue exists (filed at libtmux as part of this PR) but that's branch-internal narrative; users running the shipped wait_for_text don't need to know about a follow-up investigation issue to use the tool correctly.
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Code reviewFound 2 issues:
Lines 28 to 44 in 91ea744 AGENTS.md rule: Lines 419 to 421 in 91ea744
libtmux-mcp/tests/test_pane_tools.py Lines 2072 to 2076 in 91ea744 🤖 Generated with Claude Code - If this code review was useful, please react with 👍. Otherwise, react with 👎. |
…y_limit once The risk-band warning's `advanced` conjunction (state.history_size > entry.history_size OR state.cursor_y != entry.cursor_y) gated the warning on the wait having moved since entry. Three real cases that warning was meant to cover slipped past it: * Entry already in the risk band, idle wait -- no output happens, nothing advances, warning never fires even though the baseline is in dangerous territory from tick zero. * Cursor pinned at the bottom row of the visible region -- subsequent scrolls advance history_size but leave cursor_y unchanged; if hsize also stayed at the cap across two polls, advanced returned False. * Trim+scroll bounce keeping hsize stable at the cap -- entry at 49, every subsequent poll also sees 49; advanced returns False. Drop the conjunction. The one-shot warned_risk_band flag is already the right noise filter -- it limits warnings to one per call regardless of how long the wait sits in the band. Firing on any tick where state.history_size >= risk_floor catches all three cases. Also cache baseline_hlimit at entry instead of re-reading state.history_limit each tick. history-limit is fixed at pane creation (retroactive change only lands in tmux 3.7+), so per-tick reads are redundant. The warning message uses the cached value too. Adds test_wait_for_text_warns_when_already_in_risk_band -- pre-fills a fresh pane past the risk floor, then runs an idle wait with no further output. Asserts the warning fires anyway. Pairs with the existing test_wait_for_text_warns_in_history_limit_risk_band which covers the advance-into-the-band path.
…ooting at wait_for_channel
Two doc surfaces still recommended the send_keys -> wait_for_text ->
capture_pane pattern that the wait-family re-framing walked back:
* docs/topics/prompting.md has a "For general tmux workflows" code
block tagged ``:class: system-prompt`` -- specifically meant for
agents to copy into their AGENTS.md / CLAUDE.md / .cursorrules.
Higher leverage than tool descriptions because it shapes the
agent's mental model before any tool call.
* docs/topics/troubleshooting.md item 3 ("Timing") had the same
recommendation in a "what to check" bullet -- lower visibility
but still misleading.
Both now lead with wait_for_channel + composed tmux wait-for -S as
the deterministic primitive for command completion, and demote
wait_for_text / wait_for_content_change to "output you don't author"
duty. Matches the send_keys docstring, server instructions, and the
wait_for_text "When NOT to use this" section.
No CHANGES update -- the underlying re-framing already shipped under
### Documentation. These are stragglers being brought in line with
the announced change.
…proportions and ordering
Three corrections against the Changelog Conventions in AGENTS.md:
* **Section order.** The fixed subheading order is Breaking changes ->
Dependencies -> What's new -> Fixes -> Documentation -> Development.
The unreleased block had Documentation in the wrong slot (between
Breaking changes and Dependencies) and Fixes ahead of Documentation
out of order. Reordered to match.
* **Proportional prose.** Dropped backend-mechanism phrasing
("trim-then-scroll bounce", "sampled hsize clamped near history-limit",
"no longer falls back to raw cmd() calls") that violates the
"internal jargon" anti-pattern. The big breaking-change entry is now
three short paragraphs in user vocabulary (what changed, what
raises, what the warning means). The Dependencies entry no longer
walls-of-text 9 specific {meth} method names; it describes the
capability ("typed wrappers for tmux commands the server invokes").
* **PR ref form.** Replaced the lone `(#45 follow-up)` qualifier with
bare `(#45)` to match the project's pattern across 25+ other entries.
The Documentation entry also picks up the doc-fragment work that
Phase 12 + Phase 14a actually shipped (quickstart, gotchas, prompting,
troubleshooting, recipes, send-keys topics), not just the three
docstring surfaces named originally.
The reordered breaking change pair leads with the bigger semantic
change (waits for new output) and follows with the syntactic break
(content_start / content_end removal) so readers see the meatier
fix first.
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Closes #45.
What changed for users
wait_for_textbecomes a "wait for output written after this call" primitive instead of "match anything currently in the pane." For agents whose first poll used to returnfound=Trueon stale scrollback, this is a real fix. The CHANGES## libtmux-mcp 0.1.x (unreleased)section describes the published-release-reader contract.Concrete user-visible changes vs
0.1.0a6:(history_size, cursor_y)at entry; only matches lines written after the call begins.content_start/content_endparameters removed (the anchor supersedes them).-Jflag — long error strings that wrap across rows now match.pattern, sub-10 msinterval, non-positivetimeoutat entry.ToolErroron pane death, pane respawn, orclear-historymid-wait.notifications/messagewarning when polling approacheshistory-limit— the band where tmux'sgrid_collect_historytrim+scroll bounce keepshsizeclamped at the cap and the strict-shrink guard can't catch every trim.send_keysdocstring, andwait_for_textdocstring all point agents atwait_for_channel(composed withtmux wait-for -S) as the deterministic primitive for command completion. The polling-scraperwait_for_textis now framed for output the agent does not author.docs/topics/prompting.mdsystem-prompt fragment anddocs/topics/troubleshooting.md"Timing" bullet brought in line with the channel-first guidance.Theoretical grounding
Reviewed against tmux source pinned at
134ba6c:cmd-capture-pane.c:158(top = gd->hsize + n)cmd-capture-pane.c:159-160grid.c:386(grid_collect_historydecrementshsizebyhlimit/10)grid-view.c:106(grid_view_scroll_region_up)screen.c:451-465(screen_resize_y)hsize:screen.c:127(screen_reinit)format.chistory format strings +options-table.chooks list both checked, no monotonic counter orhistory-trimmedhookThe rollover detection's partial coverage is acknowledged explicitly. A 2 ms high-frequency probe across ~3000 samples confirmed there is no sub-poll window where
hsizedips below entry once entry was sub-cap — so the strict-shrink guard catchesclear-historyand the entry-at-cap edge but not bursty trim. The runtimectx.warningin the trim-risk band is the agent-facing mitigation;wait_for_channelis the deterministic alternative.Test plan
Green at every commit. 461 tests pass.
New regression tests cover: stale scrollback no-match (#45), bottom-row clip, mid-wait respawn, pane death under
remain-on-exit, input rejection (empty pattern / tiny interval / non-positive timeout), wrap-spanning patterns, resize-grow not raising, history shrinking viaclear-historyraising, idle wait already in trim-risk band warning, burst wait advancing into trim-risk band warning, cancellation propagation, server instruction substring assertions,send_keysdocstring cross-link.Filed follow-ups (deferred, not in this PR)
wait_for_texttwo-call state/capture race within a single tick (architecture)include_baseline_row=Trueopt-in for same-row writes (enhancement)wait_for_content_changelifecycle parity withwait_for_text(enhancement)Breaking changes
content_start/content_endparameters removed fromwait_for_text. Pre-alpha API; CHANGES carries a before/after block.wait_for_textraisesToolErroron emptypattern,interval < 0.01,timeout <= 0, pane death, pane respawn, andhistory_sizeshrink below entry baseline. Previously most of these silently miscaptured or returnedfound=Falseafter the full timeout.