fix(panel): the #779 silence detector — a selected tab that never paints must say so, verified live on real 1.50.3

[artokun]

What this PR is, and what it is not

The blank-panel-on-1.50.x cause was already fixed on main before this branch existed: #784 (the sidebar guard must not destroy on an unknown active tab), #785 (a throwing render() paints a failure shell instead of nothing), #786 (the second reader of the moved tab-button marker). The sidebar-tab contract never moved — 1.50.3 calls render(); our own guard deleted the content the instant it was attached.

This PR is the two halves that were still missing:

1. The silence detector — the diagnostic that would have made Agent panel renders completely blank on a fresh 0.11.44 install — tab registers, content never paints, no error attributed to us #779 a one-line support answer, and the only thing that will speak the next time a frontend change breaks us in a way nobody predicted.
2. Live verification on a real 1.50.3 — which the fix(panel): the sidebar guard must not destroy on an UNKNOWN active tab #784 thread explicitly recorded as still owed ("I would still rather see the panel render on a real 1.50.3 before calling it confirmed").

Closes #779 (the issue auto-closed when #784 merged; this branch carries the remaining halves discussed in its thread).

1. The watchdog (web/js/lib/sidebar-render-watchdog.js)

#785 covers a render() that throws. A render() that is never called — which is exactly what a real sidebar-tab contract change in a future frontend would produce — still failed in perfect silence. Two evidence-only checks close that:

• Starvation: our tab is provably the selected one (dual-generation marker read via the fix(panel): the sidebar guard must not destroy on an UNKNOWN active tab #784 helper — data-testid first, class fallback) and neither .cmcp-root nor the fix(panel): a blank tab is never an acceptable failure state #785 failure shell exists, continuously for 3s, re-verified at expiry. One console.error, ever, naming the panel version, the frontend version, that it is not a connection problem, that reinstalling cannot help, where to report, and a working --front-end-version pin.
• Appearance: the sidebar rail exists but our tab button never joined it within 10s of the rail being seen — the shape of a frontend that accepts registerSidebarTab() and silently drops the legacy spec. Same message structure.

The false-positive bar was treated as the primary requirement, because this line will be read as "something is broken":

• an unreadable tab marker disarms rather than counts — the fix(panel): the sidebar guard must not destroy on an UNKNOWN active tab #784 lesson applied to diagnostics ("I cannot tell" must never be reported as "it is broken");
• no rail recognized = permanent silence, watchdog-wide (hardened in codex round 1);
• keep-alive detaches (user switches tabs mid-window) disarm; a slow first build is absorbed by the deadline re-check — it fires on fresh evidence, never a stale sample; a stalled main thread cannot fire early, because the deadline is itself a timer;
• a glimpse of paint retires nothing — only a paint that survives 1.5s while our tab is active retires the watchdog. This is not theoretical: the first draft trusted the glimpse, and a live drill reproducing the actual Agent panel renders completely blank on a fresh 0.11.44 install — tab registers, content never paints, no error attributed to us #779 shape (root attached, then removed in the same mutation flush) put the watchdog to sleep instead of firing it. Caught live on the rig, fixed, re-drilled on both frontends, and pinned by unit tests.

The remedy line, corrected against reality

The pin names Comfy-Org/ComfyUI_frontend — not comfyanonymous/ComfyUI, the spelling the issue thread circulated. The flag fetches GitHub releases from the repo it names; the frontend's 1.x tags exist only in the frontend repo, and the wrong spelling silently falls back to the installed default package (watched happen in a live boot log; confirmed against 0.30.2's frontend_management.py and the GitHub API). The pin also derives from VERIFIED_FRONTENDS (#787's registry) and prefers the newest verified frontend that differs from the one failing — never a hardcoded relic, never the version the user is already stuck on.

The wording (starvation; appearance is analogous)

[comfyui-mcp-panel] the Agent tab has been selected for ~3s but no panel content exists (no .cmcp-root in the document). The tab registered and was selected, yet the panel was either never asked to render or its content was removed as soon as it was attached. That is a compatibility fault between panel <ver> and ComfyUI frontend <ver>. This is NOT a connection problem, and reinstalling the pack or ComfyUI cannot change it. Please report it at <issues> and include both version numbers from this message. Until it is fixed, relaunching ComfyUI with --front-end-version Comfy-Org/ComfyUI_frontend@<pin> restores the panel (frontends 1.47.12 and 1.50.3 are verified to render this panel version).

It reports what was observed (naming both shapes it cannot distinguish), never a guessed cause — the same rule as #785, learned from the hour this reporter spent reinstalling on a guess.

2. Verification — all live, real browsers, real frontends

Isolated second ComfyUI instance (CPU, scratch --base-directory, this branch via junction, port 8388) — the owner's rig on 8188 was never restarted or repointed.

check	frontend	result
panel renders, .cmcp-root connected + visible	1.50.3 (real bundle, data-testid-only buttons)	PASS — the verification the #784 thread recorded as owed
keep-alive: detach on switch-away, re-attach on return	1.50.3	PASS
watchdog silent through open → dwell → switch → return	1.50.3	PASS (0 lines)
drill: root removed on attach (the historical failure shape)	1.50.3	PASS — exactly one line, names frontend 1.50.3, pin backs off to @1.47.12
panel renders + keep-alive + watchdog silent	1.47.12 (this branch)	PASS
drill: root removed on attach	1.47.12	PASS — exactly one line, names frontend 1.47.12
main's #784–#786 render + keep-alive, no panel console errors	1.47.12, owner's live rig, read-only	PASS

Static cross-check of the extracted 1.50.3 bundle confirmed every marker this branch depends on: "data-testid":\${e.id}-tab-button`, side-bar-button-selected, side-tool-bar-container, and mountCustomExtension=(e,t)=>{e.render(t)}` (render IS invoked; no handler).

Unit: 29 watchdog tests (state machine, both wordings, installer against a hand-cranked clock and fake rail in both marker generations, the live-drill regression, integration greps). Full suite 3045/3045. The #787 DOM-reach gate passes — the watchdog reads only already-declared selectors, whose registry entries now name it as a reader.

Codex self-gate: round 1 raised two P1s — one accepted and fixed (pre-rail arming hole), one declined with reasons and pinned by a test (appear-then-vanish is out of the "never appeared" charter). Round 2: PASS.

Out of scope, deliberately

• No version bump — releasing (which every 1.50.x user is still waiting on; main is unreleased at 0.11.44) belongs to the release owner.
• The TODO(v2): defineSidebarTab migration stays a TODO: the contract demonstrably did not move, and migrating under a P0 label would be churn, not fix.
• Playwright browser tests were not run (they require --workers=1 against the live ComfyUI and are not in CI); the checks above were performed directly in a real browser instead.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds a sidebar render watchdog to diagnose blank or missing Agent tabs.

Changes:

• Detects render starvation and missing tab buttons.
• Reports panel/frontend versions with recovery guidance.
• Adds comprehensive watchdog unit tests and DOM dependency documentation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
web/js/lib/sidebar-render-watchdog.js	Implements watchdog detection and reporting.
web/js/lib/comfyui-dom-deps.js	Documents added DOM dependencies.
web/js/comfyui-mcp-panel.js	Installs the watchdog after tab registration.
browser_tests/unit/sidebar-render-watchdog.test.mjs	Tests reports, state transitions, and integration.

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[artokun]

Superseding the earlier body: this was never stranded work — the worktree was live and mid-verification when it was surfaced (the same file-heuristic trap as the documented dont-kill-agents-on-file-heuristics incident). The branch is now COMPLETE and fully verified: live on a real 1.50.3 (isolated second instance, correct Comfy-Org/ComfyUI_frontend pin via local dist cache) and on 1.47.12, healthy paths silent, drills fire exactly one correctly-worded line on both frontends, codex gate round 2 PASS, full suite 3045/3045. See the updated PR body for the verification table. Not merging — that call belongs to the merge/release owner.