[teamleaderleo]

SW-04: closed running tray stops building hundreds of invisible row elements

The default agent-pane SubagentTray starts folded when more than three agents/commands are running. Its render nevertheless unconditionally maps every live and completed item through line(item) into React <li> children before the return statement. The returned JSX already gates the fold body using useFold(...).present. At 300 active agents, a fully collapsed tray builds 300 AgentLine trees on every render (including its elapsed-time header tick), discarding those trees because the fold body is absent.

Change: construct cards only while fold.present is true. This exact existing hook stays true while a close animation is playing, so open/close animation and focus semantics are preserved. Once it has finished closing, no hidden row creation. Header count, oldest elapsed time, stop semantics, arrival identity tracking, View all and full open tray are unchanged. The shared AgentsPill.nestAgents helper also now appends to indexed sibling groups instead of cloning the prior array for every sibling, preserving order and the existing fallback for cyclic parent links.

Regression: webviews/test/subagent-tray.test.tsx covers 300 siblings and a historical parent cycle, plus adds 300 agents with observable name reads. Before opening, the collapsed tray must have zero AgentLine DOM rows and zero name reads during row construction; expanding must show all 300 and read their names. This tests the render cost that DOM-count-only coverage missed (the old implementation also had zero mounted rows but created 300 hidden element trees).

Source: feat-cmux-next@38550c7743b27f346ae45b75fbd72cbda80af737; branch sw04-skip-collapsed-tray-rows, head 01a768bbfdd335dc2cd30c3869aee865b8b1316b. Three files changed (tray, shared pill nesting helper, focused tray tests). No daemon, Chief or wire contracts changed. A separate active #27886 owns workflow progress and is not modified.

Validation: source-only from this chat; new webview test was committed but the repository bun suite has not been executed here. Gate on cd webviews && bun test test/subagent-tray.test.tsx, bun run check, and a narrow Mac live tray open/close capture if needed.

Performance

Metric	Before	After	Delta	Harness or run link
Hidden row name reads, first render of a folded 300-agent tray	1200	0	-1200	cmux-ci job ef23bb758f5d739c562c2785
Hidden row name reads per header rerender (folded, 300 agents)	600	0	-600	same job
Median folded rerender, ms (jsdom, 50 renders)	0.601	0.119	-80.2%	same job

Harness: webviews/test/sw04-bench.test.tsx (uncommitted bench; before = feat-cmux-next's code, after = this PR's, same process), run on the fleet Linux pool via cmux-ci test, job ef23bb758f5d739c562c2785, source 4f1a46121bd7. No new timer, observer or animation loop; the fold keeps its existing cleanup.

Capture

No capture: the closed tray is visually the same header; open/close motion and results are unchanged. The user-visible difference is lower invisible work, to be validated under a signed NEXT build.

Related SW-04 results and other narrow PRs: HQ #5599.

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Summary by cubic

Stops the folded SubagentTray from building hundreds of invisible row elements on every render. Previously the tray mapped every live and completed agent through line(item) into <li> children regardless of fold state, so 300 collapsed agents constructed 300 AgentLine trees per header tick and discarded them. Rows are now built only while fold.present is true, which stays true during close animation so open/close motion and focus behavior are preserved.

The shared AgentsPill.nestAgents helper now appends to indexed sibling groups instead of cloning the prior array for every sibling, preserving order and the fallback for cyclic parent links.

• Adds regression tests for 300 agents: zero row name reads while collapsed (including a repeated collapsed render), 300 rows after expanding, and nesting order with a cyclic parent fallback.

^{Written for commit 87cc164. Summary will update on new commits.}

[blacksmith-sh]

Found 10 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmp5w9sp62q/summary-missing.json (live):/summary-missing.json (live):	View Logs
/tmp/tmpof9nsfjr/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
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
test_every_listed_hook_is_one_glaeda_released_with_the_check (main.SigningHooksInSt epWithGlaedaTests.test_every_listed_hook_is_one_glaeda_released_with_the_check)/ test_every_listed_hook_is_one_glaeda_released_with_the_check (main.SigningHooksInSt epWithGlaedaTests.test_every_listed_hook_is_one_glaeda_released_with_the_check)	View Logs
test_every_part_of_bun_run_check_runs_in_the_warn_branch (main.WebviewsWarnSplitCov ersCheck.test_every_part_of_bun_run_check_runs_in_the_warn_branch)/ test_every_part_of_bun_run_check_runs_in_the_warn_branch (main.WebviewsWarnSplitCov ersCheck.test_every_part_of_bun_run_check_runs_in_the_warn_branch)	View Logs
test_no_runner_picker_returns_a_hosted_mac (main.NoHostedMacInNightlies.test_no_run ner_picker_returns_a_hosted_mac)/ test_no_runner_picker_returns_a_hosted_mac (main.NoHostedMacInNightlies.test_no_run ner_picker_returns_a_hosted_mac)	View Logs

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

[github-actions]

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

Review 87cc164: 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=pr29250 -f ref=sw04-skip-collapsed-tray-rows -f platform=macos -f backend_mode=local

Gallery before/after for 87cc164: 16 states rendered, 24 images differ, 392 more touched states not rendered. Images are in the run's artifact, not on this public PR; the independent review of this head reads them on its own, so the PR needs no hand-made screenshots of these states.

gh run download 41289635760 -R manaflow-ai/cmux -n gallery-advisory-29250-87cc164cbc694326a2110e77957b82101057f6d4 (then read gallery-review.json)

States

State	Theme	Status	Diff	Picked by
agent-pane.subagent-row-anatomy/done-one	Apple System Colors Light	unchanged	0%	own SubagentTray.tsx
agent-pane.subagent-row-anatomy/done-one	Apple System Colors	unchanged	0%	own SubagentTray.tsx
agent-pane.subagent-row-anatomy/running-stats	Apple System Colors Light	changed	0.0432%	own SubagentTray.tsx
agent-pane.subagent-row-anatomy/running-stats	Apple System Colors	changed	0.0116%	own SubagentTray.tsx
agent-pane.subagent-row-anatomy/mixed	Apple System Colors Light	changed	0.0129%	own SubagentTray.tsx
agent-pane.subagent-row-anatomy/mixed	Apple System Colors	changed	0.0122%	own SubagentTray.tsx
agent-pane.subagent-tray/grid-31	Apple System Colors Light	changed	0%	own SubagentTray.tsx
agent-pane.subagent-tray/grid-31	Apple System Colors	changed	0%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-two	Apple System Colors Light	changed	0.0211%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-two	Apple System Colors	changed	0.0169%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-one-running	Apple System Colors Light	changed	0.0124%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-one-running	Apple System Colors	changed	0.0086%	own SubagentTray.tsx
agent-pane.subagent-tray/short-dock	Apple System Colors Light	unchanged	0%	own SubagentTray.tsx
agent-pane.subagent-tray/short-dock	Apple System Colors	unchanged	0%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-118	Apple System Colors Light	changed	0%	own SubagentTray.tsx
agent-pane.subagent-tray/panel-118	Apple System Colors	changed	0%	own SubagentTray.tsx
agent-pane.subagent-tray/workflow-progress	Apple System Colors Light	changed	0.0132%	own SubagentTray.tsx
agent-pane.subagent-tray/workflow-progress	Apple System Colors	changed	0.01%	own SubagentTray.tsx
agent-pane.subagent-tray/one-running	Apple System Colors Light	changed	0.0114%	own SubagentTray.tsx
agent-pane.subagent-tray/one-running	Apple System Colors	changed	0.0108%	own SubagentTray.tsx
agent-pane.subagent-tray/duration-columns	Apple System Colors Light	changed	1.8%	own SubagentTray.tsx
agent-pane.subagent-tray/duration-columns	Apple System Colors	changed	0.0319%	own SubagentTray.tsx
agent-pane.subagent-tray-head/folded	Apple System Colors Light	changed	0.0404%	own SubagentTray.tsx
agent-pane.subagent-tray-head/folded	Apple System Colors	changed	0.0353%	own SubagentTray.tsx
agent-pane.subagent-tray-head/open	Apple System Colors	changed	0.0429%	own SubagentTray.tsx
agent-pane.subagent-tray-head/open	Apple System Colors Light	changed	0.0425%	own SubagentTray.tsx
agent-pane.subagents/agents-pill	Apple System Colors Light	changed	0.0459%	own AgentsPill.tsx
agent-pane.subagents/agents-pill	Apple System Colors	unchanged	0%	own AgentsPill.tsx
agent-pane.subagents/running	Apple System Colors Light	unchanged	0%	own AgentsPill.tsx
agent-pane.subagents/running	Apple System Colors	unchanged	0%	own AgentsPill.tsx
agent-pane.subagents/mixed	Apple System Colors Light	changed	0.0342%	own AgentsPill.tsx
agent-pane.subagents/mixed	Apple System Colors	unchanged	0%	own AgentsPill.tsx

_{Pick other states with a Gallery: entry.id, entry.id/variant line in the PR body.}

Passes: CI passes on 87cc164cbc.

CI passes on 87cc164cbc (run 41269107539 attempt 1).

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.

red: cmux-next checks (god files, concurrency, crash safety, l10n); base red: the same failure on the base 2809196; does not block

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4130052256501 (28aa638015)

[teamleaderleo]

Awareness note from an agent lane that does not own this PR; it is not a review or a request to take the PR over.

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Carrying all five authored commits in #29794 together with the tray alignment and folding fixes, preserving the hidden-row and sibling-index regression coverage.

[teamleaderleo]

Review (claude opus, correctness first): SHIP at 87cc164

Read the full diff against feat-cmux-next. cards was only ever rendered inside {fold.present && ...}, so building it only while fold.present changes no output: fold.present stays true through the close animation, and arriving() (refs and entrance bookkeeping) runs only for rows that mount, as before. nestAgents now pushes into the existing sibling array instead of copying it; order and the cycle fallback are unchanged, and both have tests. Webview shards (react-apps-base-check 1-8) are green at this head. The other reds are risk evidence (it waits for this review) and cmux-next checks, which fail the same way on base.
Follow-ups: none blocking. #29885 carries these same commits; identical hunks merge cleanly.