[teamleaderleo]

What this fixes

Three suites fail on the feat-cmux-next tip: ColumnStripFitTests, ColumnCloseMotionTests and DividerCursorUnderDockTests (tip suite job). All three come from one line in ColumnStripGeometry.frames, added by 0f8696c ("fix(layout): columns that fit the strip end on the viewport edge"):

let room = viewport.width - gap - x
if width > room { width = max(1, room) }

The commit meant to trim rounding: equal columns, each rounded to a pixel on its own, overflowed by up to 1.5 pt. The line trims any column past the trailing edge, though, including one that is meant to overflow:

• A second full-width column collapses to 1 pt. In ColumnCloseMotionTests, revealing it leaves the chat on screen.
• A 0.6 column no longer runs on under a right dock. DividerCursorUnderDockTests finds no divider under the dock.
• Rounded-down columns still stop short. In ColumnStripFitTests, equal columns end 0.25 to 2.25 pt before the edge.

The change

A column now takes the room left in two cases, and only before any column was widened to its minimum:

• it fits before rounding, and rounding pushes it past the edge;
• its unrounded end is the trailing edge.

A column whose own fraction runs past the edge keeps its width, and the strip scrolls, as it did before 0f8696c.

Test changes

• New test, aColumnPastTheEdgeKeepsItsWidth: two full columns stay equal and the strip scrolls.
• Changed expectation, screenGeometryOfEqualColumnsHasNoOverflow: it still requires zero overflow wherever the equal share is at least the column's minimum width. Below that minimum it now expects the strip to scroll. Columns widen to the pane minimum so panes never collapse; that is the existing minimumWidths contract. The old expectation (fit 5 columns into 600 pt) contradicted it, and the 23 to 435 pt "overflow" in that check is that widening.

Order this serves:

"Find the common failure ... fix it so swift test goes green on base, and confirm on PR runs. A base red that hides signal blocks Swift-surface landings until it's green"

Source change: 0f8696c, with its test c35c180. This is a minimal forward fix that keeps that commit's intent (no overflow from rounding).

No capture: a pure geometry fix whose visible effect (columns end on the strip edge; a second full column or a column under a dock keeps its width) is asserted pixel-exact by the three suites above. Two cmux-ci capture --state tour:core attempts on fleet minis released their lease before the app could be driven ("the lease has 13s left" and "45s left: too little to drive the app").

Risk: low. Pure geometry, one function, covered by the three suites above.

Review (codex gpt-6-astra xhigh): SHIP at fa681c4

Agent session: agent session

🤖 Generated with Claude Code

[teamleaderleo]

Owned by an agent session · session

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review fa681c4: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr26100 -f ref=fix/next-column-strip-base-red -f platform=macos -f backend_mode=local

red: cmux-next checks (god files, concurrency, crash safety, l10n); no finished base run on 8ff9fcf to compare; do not merge until green; see lane-rules

[blacksmith-sh]

Found 15 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmp0p8_o4_4/summary-fail.json (live):/summary-fail.json (live):	View Logs
/tmp/tmpsc2dp4at/summary-missing.json (live):/summary-missing.json (live):	View Logs
[new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows/ [new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows	View Logs
[new_workspaces] the window draws no frames/[new_workspaces] the window draws no frames	View Logs
[tabs] debug.tab_switch timed 0 of 40 switches/ [tabs] debug.tab_switch timed 0 of 40 switches	View Logs
[tabs] the window draws no frames/[tabs] the window draws no frames	View Logs
main.DeveloperIdAppTests.test_download_prints_the_active_profile_only/ test_download_prints_the_active_profile_only	View Logs
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
stubs: /System/Library/Frameworks/Security.framework/Versions/A/Security has no stub/ Security has no stub	View Logs
stubs: CoreFoundation.tbd: install-name /System/Library/Frameworks/ CoreFoundation.framework/Versions/A/CoreFoundation, missing 1: ['_CFRetain']/ CoreFoundation, missing 1: ['_CFRetain']	View Logs

...and 5 more test failures. View all on Blacksmith: run 40481711284, run 40481710740

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[teamleaderleo]

Bead cx-5luhpt created for this PR by the cmux coordinator.

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4050816581101 (88afd5fb41)
• cmux NEXT nightly 1.0.0-nightly.4050852156901 (baa0bf0028)
• cmux NEXT nightly 1.0.0-nightly.4051163715101 (3dbd6fe575)
• cmux NEXT nightly 1.0.0-nightly.4051466928001 (57dd76e81c)
• cmux NEXT nightly 1.0.0-nightly.4051568197101 (5d261477be)
• cmux NEXT nightly 1.0.0-nightly.4052516359101 (86ebb89edf)
• cmux NEXT nightly 1.0.0-nightly.4055612617201 (f83ddd6b20)