Headed E2E default drops required frame-rate override

Context

PR #16138 resolved #16128 by making PRESENTING_LAUNCH_ARGS the unconditional headed-E2E default. At dev head be17257b3f, that profile is defined by filtering --disable-frame-rate-limit out of BASE_LAUNCH_ARGS; only exact NEO_E2E_ENGINE_PROFILE=1 restores the flag.

Post-merge physical evidence on the active macOS Workstation seat reverses that ticket's premise: ordinary/default launches opened multiple real Chrome windows whose semantic app state stayed live while the visible windows were completely empty. The controlled rerun with --disable-frame-rate-limit present rendered application content. The operator identified animated OffscreenCanvas work as a likely contributor; that mechanism remains a hypothesis and is not required to repair the launch contract.

This is new evidence after the predecessor resolved, so it needs a successor rather than reopening #16128.

Live latest-open sweep: checked the 30 newest open issues plus the 50 most recent A2A messages at 2026-07-29T22:32:47Z; no equivalent ticket or in-flight claim exists.

The Problem

The launcher now encodes the wrong baseline for UI tests:

standard E2E command
→ activeLaunchArgs() with no sentinel
→ PRESENTING_LAUNCH_ARGS
→ BASE_LAUNCH_ARGS without --disable-frame-rate-limit
→ physically empty native windows on the current seat

An empty-window profile is not a valid UI-test profile. Worker, DOM, and Neural Link assertions can remain green while the visual subject does not exist, producing a semantically plausible false-green receipt.

This must not be a flag peers remember, a sentinel they select, or a host-specific command copied between sessions. The standard E2E configuration must include the required launch baseline automatically. Specialized profiles may add benchmark or GPU-intent flags; no UI-test profile may remove the flag required to render content.

The Architectural Reality

• test/playwright/e2e/utils/gpuIntent.mjs is the single launch-argument authority. Its current default removes the required flag.
• test/playwright/playwright.config.e2e.mjs passes activeLaunchArgs() to both gl-probe and the Chromium project, so the selector owns the physical browser process rather than documentation alone.
• NEO_E2E_ENGINE_PROFILE=1 selects additional GPU-intent/benchmark flags. That distinction may remain useful, but it must not decide whether application pixels exist.
• NEO_FILM_TAKE=1 is a pacing/recording signal in Workstation specs. It must not carry browser-correctness responsibility.
• The earlier #15912 / #16128 evidence described a historical host/harness observation. The new post-merge physical receipt proves that it cannot remain an unqualified universal launch contract.
• No product-side docking class owns this problem. The repair belongs in the E2E launch authority and its focused selector tests.

The Fix

1. Make --disable-frame-rate-limit an unconditional member of the shared UI-test browser baseline.
2. Make the no-sentinel/default activeLaunchArgs() result inherit that baseline.
3. Make every retained UI-test variant—including film and engine/benchmark selection—inherit the same baseline. A specialized variant may add flags, but it must not remove --disable-frame-rate-limit.
4. Remove the flag-less PRESENTING_LAUNCH_ARGS UI profile. If a future non-UI experiment needs a flag-less browser, it belongs behind a separate explicitly non-visual harness contract, never the E2E UI default.
5. Keep film pacing/recording semantics independent of browser launch correctness.
6. Update launcher JSDoc and affected comments so the ordinary command is the whole user contract; peers should not need to know this flag exists.
7. Pin the selector with focused tests and retain an exact-head headed Workstation screenshot showing populated application pixels under the ordinary no-sentinel command.

Contract Ledger

Acceptance Criteria

• With all E2E profile sentinels unset, activeLaunchArgs() contains --disable-frame-rate-limit.
• Every exported launch list consumed by the E2E UI configuration contains --disable-frame-rate-limit.
• Film-only, engine-only, false-like, arbitrary, and ordinary selector values all retain --disable-frame-rate-limit; profile selection can only add or otherwise tune flags.
• No UI-test command, spec, or peer workflow needs to set NEO_E2E_ENGINE_PROFILE merely to obtain rendered content.
• Both the GL probe and Chromium project consume the same corrected default list.
• An exact-head headed Workstation witness launched with the standard no-sentinel command passes and retains a populated application frame; semantic-only green is insufficient.
• No touched JSDoc, runner example, or test comment instructs peers to remember the flag or calls a flag-less path the safe/default presenting profile.
• The PR records the superseded evidence boundary: historical #15912 / #16128 host observations do not override the current physical receipt.

Out of Scope

• Product-side QT docking fixes or visual taxonomy work from #15955.
• Diagnosing the likely animated-OffscreenCanvas mechanism before restoring the safe default.
• Film editing or capture choreography.
• Reopening resolved #16128 or #15912.
• Proving a universal Chromium rule across every host; this ticket repairs the repository UI-test contract from current physical evidence.
• Running another known-invalid flag-less headed window merely to reproduce emptiness again.

Avoided Traps

• Documentation-only reminder: rejected; the ordinary command must already be correct.
• Engine-profile workaround: rejected as the UI contract; peers should not need to know or remember the flag.
• Semantic assertion as visual proof: rejected; this failure class keeps worker truth green behind empty windows.
• Flag-less “presenting” variant: rejected for UI tests; a profile with nothing to present cannot establish UI evidence.
• Bundling with a docking product ticket: rejected; launch authority is independently owned and one-PR-resolvable.
• Reopening the predecessor: rejected; the regression is post-merge successor evidence.

Related

Successor to #16128 and PR #16138.

Related: #15912, #15955.

Decision Record impact: none.

Origin Session ID: 019fac4d-7844-7422-9486-7f73ccf308f5

Retrieval Hint: "post-16138 default drops disable-frame-rate-limit empty headed Workstation windows"