[teamleaderleo]

Leo, 2026-11-03: "likewise i don't want to see flickers of the session info or anything when there's random re-renders EVER"

Closes #33201. Builds on #33203, which stopped Session Info from re-rendering on every streamed update. This PR adds the painted-frame guard the issue asked for: it covers the chat header too, runs in WebKit as well as Chromium, and drives the real pane instead of a harness.

What flickered

Nothing, at base or at the commit just before #33203 (a86fae3). Every Session Info box (the panel, the Environment and Context sections and their bodies) and every chat header box (the header, its status slot, its tools) kept the same element, the same box, the same opacity and visibility, and its text, on every painted frame of the stream. No animationstart, transitionstart or transitionrun fired inside either one, and no element was removed from either one. The re-renders #33203 removed never reached the screen as a visible flicker. So this PR changes no product code and lands the test as a guard.

Test

webviews/test/agent-pane-streaming-no-flicker.test.ts (browser lane, Chromium and WebKit). The test serves the pane's dev entry and connects it to a stand-in acpmux. It turns Session Info on, then streams a long turn: 12 steps, each sending reply tokens one word at a time, a tool call that starts and finishes, and a usage tick with session_changed. After every painted frame (support/paintedFrames.ts) it reads each box of Session Info and of the header. It fails on any of these:

• a remount (a new element, or an element removed per the MutationObserver)
• a box that moves or resizes by more than 0.5 px
• an opacity or visibility change
• a box that had text and paints empty
• an animation or transition that starts

A control at the end of the test replaces a section with a copy, dims the header for one frame and starts a CSS animation on a header tool. It asserts that the sampler reports all three, so a green run means nothing flickered, not that the sampler saw nothing.

Command: cmux-ci test --setup playwright -- bash -c 'export "$(bash scripts/ci/ensure-system-chrome.sh --optional | tail -1)"; cd webviews && CMUX_BROWSER_TESTS=1 bun test test/agent-pane-streaming-no-flicker.test.ts'

run	chromium frames	webkit frames	remounts / moves / blinks / empties / animations
base db4c64e	385	311	0 / 0 / 0 / 0 / 0
before #33203 (a86fae3)	373	287	0 / 0 / 0 / 0 / 0
head (with control)	475	392	0 / 0 / 0 / 0 / 0; control caught 2 remounts, 2 blinks, 1 animationstart in each engine

There is no red-on-base run because no flicker reproduces; the control is what shows the test can fail.

Observed / Not run

• Observed: the runs in the table above, on the fleet, both engines green, with the frame counts and the control's catches as listed. scripts/web-lint.sh (with CMUX_LOCAL_HEAVY_CHECKS=0) and prepush-gate.py are clean.
• Not run: the type-aware lint and type check, which are left to CI on this host. Sections that need a daemon with a git worktree, subagents or tasks (Changes, Tasks, Agents) do not appear in the stand-in, so the test does not cover them.

Changelog

none

Agent session: agent session

🤖 Generated with Claude Code

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Summary by cubic

Adds a guard test that a streamed agent turn never flickers Session Info or the chat header, in Chromium and WebKit.

• Drives the real pane's dev entry with a stand-in acpmux over a long streamed turn, sampling every painted frame for remounts, layout shifts, opacity/visibility blinks, empty text, and starting animations or transitions.
• A control at the end confirms the sampler catches each kind of flicker, so a green run means nothing flickered.
• No product code changes; no flicker reproduces at base, so this lands as regression protection for the issue's "no flicker ever" requirement.

^{Written for commit 3506a43. Summary will update on new commits.}

[github-actions]

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

Review 3506a43: 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=pr33526 -f ref=lane/si-no-flicker -f platform=macos -f backend_mode=local

Unclear: web / react-apps-check failed: no known signature; failed step: Check webview test shards. This PR merged before its CI finished: fix forward on main.

CI failed on 3506a43f5e (run 41612168964 attempt 1): 1 code, 1 unknown.

Job	Verdict	Why
web / react-apps-check (1)	code	a web test failed
web / react-apps-check	unknown	no known signature; failed step: Check webview test shards

Failures:

• seen on other PRs message-preview-browser.test.ts sent preview has no fade or partial chip and Show more reveals all of it: failed (job)

Matched log lines

web / react-apps-check (1): (fail) sent preview has no fade or partial chip and Show more reveals all of it [6335.90ms]

Not re-run automatically: web / react-apps-check (1), web / react-apps-check are not machine failures.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's; yours means the failing file is one this PR changes, also red on main that main's latest full suite fails the same way, seen on other PRs that it failed on another pull request's run lately.

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4162023985101 (c8f5046a98)

[blacksmith-sh]

Found 6 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmp39hc0tdv/summary-missing.json (live):/summary-missing.json (live):	View Logs
/tmp/tmpviba5geh/summary-fail.json (live):/summary-fail.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

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

[teamleaderleo]

Review (subagent claude-opus-5-5 medium): SHIP at 3506a43

Visual verdict: unchanged by this diff

Checked the test against agent-pane-turn-end-keeps-place.test.ts and support/paintedFrames.ts. Every read goes through cmuxAfterPaint or cmuxPaintFrame, and there is no requestAnimationFrame read, so check-frame-reads has nothing to flag. The stand-in daemon matches the sibling's protocol (initialize, watch, attach, events, _acpmux/event, session_changed), and requireBrowserLane plus the l10n-allow-file and cmux-web-test-timeout headers are in place. It cannot pass vacuously: it asserts the panel, header and a [data-section] key exist, asserts more than 100 frames, and a control shows the sampler catches a remount, a removal, a blink and an animation. The control's one-frame blink is safe, since the sampler's frame callback is registered before cmuxPaintFrame's and its read task is queued first.

Follow-ups: (1) only keys present on the first sampled frame are checked, so a section or header tool that mounts mid-stream is never itself checked (its effect on its neighbours' boxes still is); (2) moves and blinks stop at the first hit per key, so a report can hide a later, different flicker of the same box. Neither blocks.