Fix terminal drag hover overlay flicker

[austinywang]

Summary

• update vendor/bonsplit to render pane drop hover indicators as non-layout overlays
• keep portal-hosted terminal geometry stable while drag hover targets change
• add bonsplit regression coverage for hover overlays not resizing hosted content

Related

• closes Terminal flickers and re-renders when drag target hovers over it #1045
• bonsplit PR: Make pane drop hover overlay non-layout-affecting bonsplit#18

Verification

• cd vendor/bonsplit && swift build --build-tests
• ./scripts/reload.sh --tag fix-drop-hover-overlay currently fails on an unrelated existing compile error in Sources/Update/UpdateTitlebarAccessory.swift:324

---

Summary by cubic

Fixes terminal drag-hover flicker by updating bonsplit to render drop targets as non-layout overlays, keeping terminal geometry stable. Closes #1045.

• Dependencies
  • Update vendor/bonsplit to include the overlay fix and regression tests preventing hover overlays from resizing hosted content.

^{Written for commit e019293. Summary will update on new commits.}

Summary by CodeRabbit

• Chores
  • Updated dependency to latest version. No functional changes.

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Project	Deployment	Actions	Updated (UTC)
cmux	Ready	Preview, Comment	Mar 7, 2026 6:32pm

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 416e6157-c2ae-4681-aa7a-c98856d245f1

📥 Commits

Reviewing files that changed from the base of the PR and between 0c11bc1 and e019293.

📒 Files selected for processing (1)

• vendor/bonsplit

---

📝 Walkthrough

Walkthrough

The vendor/bonsplit submodule reference is updated to a newer commit. No functional code changes, control flow modifications, or exported entity declarations are altered. This is a straightforward dependency version bump with minimal impact.

Changes

Cohort / File(s)	Summary
Submodule Update vendor/bonsplit	Submodule reference updated from commit c5b3dd4cd314f7452bd27ffacd00ebeb19d96d17 to 6739829 with no functional code changes.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

🐰 A version bump so clean and small,
Just one line changed, no fuss at all,
The bonsplit grows to newer heights,
No flickering terminals in sight! ✨
Hop along, the code still right!

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch issue-1045-drag-hover-terminal-flicker

---

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[cubic-dev-ai]

No issues found across 1 file

[greptile-apps]

Greptile Summary

This PR advances the vendor/bonsplit submodule pointer from c5b3dd4 to 6739829 to pull in a fix (bonsplit PR #18) that renders pane drop hover indicators as non-layout overlays, preventing the SwiftUI layout engine from resizing portal-hosted terminal views whenever a drag target changes. No Swift source files in the main cmux repo were modified.

Key changes

• vendor/bonsplit bumped to 6739829bb54a2293dfcea6e6717fbe0d2e4b966b; actual implementation changes (overlay rendering, portal geometry stability, regression tests) live in the bonsplit repo.

Points to verify before merging

• The new bonsplit commit must be reachable from origin/main in the manaflow-ai/bonsplit repo (per the submodule safety policy in CLAUDE.md/AGENTS.md). The PR links to bonsplit PR Fix zsh ZDOTDIR wrapper + log parsing for -- tokens #18 but does not explicitly confirm it has been merged to main.
• The full cmux build remains unverified because of the pre-existing compile error in Sources/Update/UpdateTitlebarAccessory.swift:324. While unrelated to this change, it means CI cannot currently give a clean green signal on this bump.

Confidence Score: 4/5

• Safe to merge once the bonsplit commit is confirmed on origin/main; the change is self-contained and low-risk.
• The diff is a single submodule pointer update with no changes to cmux source files, making regression risk minimal. The score is held at 4 rather than 5 because the submodule safety policy (commit must be on main before the parent pointer is updated) has not been explicitly confirmed, and the full end-to-end build is currently blocked by a pre-existing unrelated compile error.
• vendor/bonsplit — verify the new commit SHA is on the remote main branch of manaflow-ai/bonsplit before merging.

Important Files Changed

Filename	Overview
vendor/bonsplit	Submodule pointer bumped from c5b3dd4 to 6739829; intended to change hover drop indicators to non-layout overlays and stabilise portal-hosted terminal geometry during drags. Actual bonsplit source changes are in the linked bonsplit PR #18 and cannot be reviewed here. Whether 6739829 is on bonsplit's remote main branch — required by the submodule safety policy — is unverified in this diff.

Sequence Diagram

sequenceDiagram
    participant User as User (drag gesture)
    participant BSV as BonsplitView
    participant PD as PaneDragContainerView
    participant OL as HoverOverlay (non-layout)
    participant TW as TerminalWindowPortal

    User->>BSV: begin drag over split pane
    BSV->>PD: hover target changes
    PD->>OL: show/hide drop indicator (overlay only)
    Note over OL,TW: Old behaviour: layout recalculated → portal resized → flicker
    Note over OL,TW: New behaviour: overlay is out-of-layout → portal geometry unchanged
    OL-->>TW: geometry stable (no resize event)
    User->>BSV: drop or cancel drag
    BSV->>PD: clear hover target
    PD->>OL: hide drop indicator

Loading

_{Last reviewed commit: e019293}

[greptile-apps]

Verify bonsplit commit is on remote main

CLAUDE.md and AGENTS.md both document a hard submodule safety rule:

Always push the submodule commit to its remote main branch before committing the updated pointer in the parent repo. Never commit on a detached HEAD or temporary branch — the commit will be orphaned and lost.
Verify with: cd vendor/bonsplit && git merge-base --is-ancestor HEAD origin/main

This PR points vendor/bonsplit at 6739829 and links to bonsplit PR #18, but the description does not confirm that PR has been merged to main in the manaflow-ai/bonsplit repo. If 6739829 lives only on a feature branch or a detached HEAD, it could be garbage-collected and the parent-repo pointer would become dangling.

Please confirm the bonsplit commit is reachable from origin/main before merging.

[greptile-apps]

End-to-end build is unverified

The PR's verification section notes:

./scripts/reload.sh --tag fix-drop-hover-overlay currently fails on an unrelated existing compile error in Sources/Update/UpdateTitlebarAccessory.swift:324

While the failure is attributed to a pre-existing issue, it means the full cmux build with this new bonsplit version has not been confirmed clean. If the pre-existing error is blocking CI it may mask any new failures introduced by this bonsplit bump. Consider tracking the UpdateTitlebarAccessory.swift:324 compile error so it does not continue to obscure build health on future PRs.