Fix #3465: stop tab indicator animation glitch

[austinywang]

Summary

• Advances vendor/bonsplit to Fix tab indicator selection chrome bonsplit#125 (78de1d7) for the tab-indicator glitch fix.
• Keeps selected-tab chrome as a computed projection of the current selectedTabId plus the measured tab frame map, removing stale selected-frame preference state from the indicator path.
• Disables incidental tab-bar hover/press/visibility animation so rapid Next/Previous Surface selection snaps the active chrome atomically.
• Bounds and hard-clips the split action lane during measurement/overflow states so the indicator and split controls keep stable geometry even before tab widths are fully known.

Repro

Steps used locally before the fix:

1. Focused a cmux workspace with a pane containing two terminal surfaces.
2. Rapidly alternated the default Next Surface / Previous Surface shortcuts (Cmd+Shift+], then Cmd+Shift+[), including a repeated near-instant sequence.
3. Observed the tab-bar active indicator/selection chrome visually transition during rapid selection instead of snapping atomically to the selected surface.

Observed: the blue active-tab indicator can visually lag or jump during rapid shortcut alternation.
Expected: the indicator tracks the selected surface immediately with no intermediate animated state.

Testing

• Not run locally per repo policy.
• Bonsplit PR Fix CJK IME input (Korean, Chinese, Japanese) #125 CI passed.
• Bonsplit coverage includes selected-frame derivation, no-animation tab-bar policy, bounded split action lane measurement, and overflow rendering checks.
• This cmux PR updates only the vendor/bonsplit submodule pointer and is being driven through required PR checks.

Closes #3465

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	May 19, 2026 5:13am
cmux-staging	Building	Preview, Comment	May 19, 2026 5:13am

[coderabbitai]

📝 Walkthrough

Walkthrough

The vendor/bonsplit submodule pointer is updated to a new commit SHA (from e1d9954a... to e293ad6173...).

Changes

Bonsplit Submodule Update

Layer / File(s)	Summary
Submodule pointer update vendor/bonsplit	The vendor/bonsplit submodule reference is updated from commit e1d9954a... to e293ad6173....

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• manaflow-ai/cmux#4121: Also advances the vendor/bonsplit submodule commit reference in a related update.

Poem

🐇 I hopped through hashes, one then two,
Bonsplit's new home snug and true,
A tiny bump, a quiet cheer,
The vendor lands a fresh new year. ✨

🚥 Pre-merge checks | ✅ 16

✅ Passed checks (16 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately reflects the main objective of the PR—fixing the tab indicator animation glitch reported in issue #3465. It is concise and specific to the primary change.
Linked Issues check	✅ Passed	The PR fully addresses #3465 objectives: disables tab-bar animations to prevent glitching and derives indicator frame from current selectedTabId and measured tab frames to ensure atomic updates during rapid selection changes.
Out of Scope Changes check	✅ Passed	All changes are scoped to the vendor/bonsplit submodule update addressing the tab indicator glitch. Author explicitly noted leaving unrelated auth-concurrency concerns out of scope, keeping the PR focused.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Cmux Swift Actor Isolation	✅ Passed	PR only updates vendor/bonsplit submodule reference. No production Swift code in main codebase modified. Submodule updates are dependency management, not subject to actor isolation review.
Cmux Swift Blocking Runtime	✅ Passed	PR updates vendor/bonsplit submodule to fix tab animation glitch. No blocking runtime primitives (semaphores, sleeps, waits, locks) introduced in main Swift code.
Cmux No Hacky Sleeps	✅ Passed	PR changes only Swift files (6 .swift) and vendor/bonsplit submodule. Check applies to TS/JS/shell only; Swift covered separately. No TS/JS/shell changes present.
Cmux Swift Concurrency	✅ Passed	PR updates only vendor/bonsplit submodule reference. Check applies to cmux-owned Swift code; rules explicitly exclude /vendor/ subtrees. No cmux code changed.
Cmux Swift @Concurrent	✅ Passed	PR only updates vendor/bonsplit submodule reference. No Swift source code changes in main repository. @concurrent check not applicable.
Cmux Swift File And Package Boundaries	✅ Passed	PR updates only vendor/bonsplit submodule reference. The custom check explicitly excludes /vendor/ path subtrees and allows vendored code. No production Swift files in the main repo are changed.
Cmux Swift Logging	✅ Passed	PR updates vendor/bonsplit submodule and refactors Web Inspector code. No logging statements added or modified. No print, debugPrint, dump, NSLog, or Logger violations detected.
Cmux User-Facing Error Privacy	✅ Passed	PR only updates vendor/bonsplit submodule; no user-facing error messages, alerts, or command output modified. The change is a visual animation fix unrelated to error messaging.
Cmux Swiftui State Layout	✅ Passed	The PR only updates the vendor/bonsplit submodule reference (from 0000000 to e293ad6...). No SwiftUI state or layout changes were made in the main codebase. The check is not applicable.
Cmux Architecture Rethink	✅ Passed	Fix converts preference-based state to computed property, eliminating stale state. Uses idiomatic transaction(animation: nil) for animation. Single owner, clear invariants.
Cmux Swift Auxiliary Window Close Shortcuts	✅ Passed	PR only updates vendor/bonsplit submodule reference; no Swift files in main repo changed. Custom check is not applicable to submodule reference-only updates.
Description check	✅ Passed	PR description is comprehensive and well-structured, covering what changed, why, repro steps, testing approach, and issue closure.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch issue-3465-tab-indicator-glitch

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[greptile-apps]

Greptile Summary

This PR bumps the vendor/bonsplit submodule to fix a tab-bar active-indicator animation glitch (#3465) that caused the selection chrome to visually lag or animate during rapid Next/Previous Surface switching instead of snapping immediately.

• The submodule advances through three commits: a regression test covering the animation policy, disabling incidental hover/press/visibility animations on tab-bar buttons, and a follow-up that corrects the indicator frame to derive from the current selectedTabId and measured tab frame map rather than stale selected-frame preference state.
• No production Swift source files in the main repo are modified; all changes are contained within the vendor/bonsplit dependency.

Confidence Score: 5/5

Safe to merge — the change is a submodule pointer bump with no direct modifications to production Swift sources in the main repo, and the three submodule commits are covered by a regression test.

The entire diff is a single submodule pointer advance. All behavioral changes (disabling tab-bar animations and fixing indicator frame derivation) are encapsulated in the vendor/bonsplit dependency and are accompanied by a Bonsplit regression test. No production Swift code in the main repository is touched, so the blast radius is limited to UI rendering of the tab indicator.

No files in the main repository require special attention; the submodule content is not directly inspectable from this review context.

Important Files Changed

Filename	Overview
vendor/bonsplit	Submodule pointer bumped from b5dd1f0 to 78de1d7, incorporating three commits: a regression test for the animation policy, animation-disable fix for tab-bar button hover/press/visibility, and a frame-derivation fix that derives the selected indicator from currentSelectedTabId rather than stale preference state.

Sequence Diagram

sequenceDiagram
    participant User
    participant cmux as cmux (Next/Prev Surface)
    participant TabManager
    participant Bonsplit as Bonsplit TabBar

    User->>cmux: Cmd+Shift+] / Cmd+Shift+[
    cmux->>TabManager: setSelectedTabId(newId)
    TabManager->>Bonsplit: update(selectedTabId, measuredTabFrames)
    Note over Bonsplit: (before fix) derives indicator frame from stale selectedFrame preference
    Note over Bonsplit: (after fix) derives indicator frame from currentSelectedTabId + tab frame map
    Bonsplit-->>Bonsplit: No animation (hover/press/visibility animations disabled)
    Bonsplit->>User: Indicator snaps atomically to selected tab

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_{Reviews (11): Last reviewed commit: "Merge remote-tracking branch 'origin/mai..." | Re-trigger Greptile}

[austinywang]

Post-CI feedback sweep:

• Greptile now reports the earlier frame-derivation and merge-history concerns as resolved.
• CodeRabbit's pre-merge Cmux Swift @Concurrent note points at Sources/Auth/AuthManager.swift::refreshSession(), which is unchanged by this Bonsplit-only PR (vendor/bonsplit submodule pointer only). I am leaving that inherited auth-concurrency concern out of scope here to avoid mixing an unrelated auth refactor into the Blue tab selection indicator glitches when rapidly switching surfaces with prev/next surface shortcuts #3465 tab indicator fix.
• All required GitHub checks are green; optional Vercel preview deployments are still queued by Vercel.