Tear-out popup flashes white between route admission and theme bootstrap

Context

The full #15252 Take 17 native corpus closes #15955's previously untested popup-birth surface. A visible white flash occurs while a tear-out popup is created mid-gesture.

The frame sequence and source falsify the obvious diagnosis: the staged about:blank window is not the white frame. The flash belongs to the final document's pre-theme bootstrap interval.

Measured Failure

A 50 ms probe series over native media SHA-256 8771781bca0cd33d8c836804d023c37214132d362074c35d195959358a3a9667 shows:

The interval is approximately 150–200 ms in this take and is visible inside the continuous product gesture.

Authority Correction

The first proposed repair—a fixed <meta name="color-scheme" content="dark">—was falsified before review.

It removes the white excursion for Workstation's dark state, but it is not theme-correct: Workstation can explicitly run neo-theme-neo-light, while a fixed dark declaration forces the opposite bootstrap canvas. content="dark light" is not a repair either; CSS Color Adjustment lets the user agent choose from that list using host preference, which is not Neo's active runtime theme.

The exact authority already exists before popup URL construction: apps/workstation/view/Workspace.mjs#openTearOutVessel() owns me.theme. That exact selected Neo theme must cross the popup boundary and govern both:

1. the final document's color scheme synchronously before MicroLoader.mjs; and
2. the child viewport's initial Neo theme before its first VDOM paint.

The existing setWorkspaceTheme() same-app fan-out remains the authority for toggles after the popup is open.

Mechanism

src/Main.mjs#windowOpen() intentionally:

1. opens same-origin children at about:blank;
2. writes a one-use native-route token into the blank realm's sessionStorage;
3. calls location.replace(stagedUrl).

That ordering was introduced by #15396 / PR #15573 because direct-opening the final URL can let a warm shared-worker child call getWindowData() before route authority exists.

The final apps/workstation/index.html begins MicroLoader.mjs; the loader imports neo-config.json, boots Main, and only then does the Stylesheet addon apply the configured boot theme and append asynchronous CSS links. A child born while the workspace is light therefore cannot infer its correct initial theme from Workstation's dark-first config or from prefers-color-scheme.

This is a #15955 navigation/bootstrap canvas gap, compounded by a cross-window initial-theme carrier gap. It is neither style-delta frame splitting nor dock add/remove churn.

Proposed Fix

1. Add the validated current me.theme to the tear-out URL before Neo.Main.windowOpen().
2. In Workstation's final document, synchronously map only neo-theme-neo-dark → dark and neo-theme-neo-light → light before MicroLoader.mjs; direct main-window boot keeps the configured dark-first default.
3. Seed the child Workstation viewport with that same validated theme before its first VDOM paint.
4. Keep the existing post-open same-app theme fan-out for later toggles.
5. Preserve the #15573 route-token ordering and all failure paths.

Architectural Requirements

• Workspace.me.theme is the popup theme authority. OS/browser preference is only a falsifier and must not choose the Neo theme.
• One carried value governs pre-paint canvas polarity and initial viewport theme; two independently inferred values are not acceptable.
• Only the two configured Workstation theme identifiers are admitted. Arbitrary query values must not become DOM classes or config.
• Preserve the staged same-origin route-token sequence. Direct-opening the final URL is not an acceptable visual shortcut.
• Keep the repair Workstation-local unless a separately justified framework contract is proven necessary.
• Do not create a parallel skin or copy the SCSS palette into HTML.

Acceptance Criteria

• openTearOutVessel() carries the exact validated me.theme into the child URL before windowOpen().
• Workstation's final document establishes the matching dark or light color scheme synchronously in <head> before MicroLoader.mjs.
• The child viewport's initial Neo theme equals the carried theme before its first VDOM paint.
• Discriminating matrix: Neo dark + host prefers light remains dark from final-document bootstrap through first themed pane.
• Discriminating matrix: Neo light + host prefers dark remains light from final-document bootstrap through first themed pane.
• The witness distinguishes staged about:blank, final-document pre-theme, and first themed viewport frames.
• Mutation control: removing or corrupting the theme carrier restores a detectable mismatch or safe configured-default fallback; it never admits an arbitrary theme class.
• Negative control: styling only staged about:blank does not satisfy the final-document or initial-viewport assertions.
• content="dark light" fails the contract because it delegates the choice to host preference.
• The same-origin native-route token is written before navigation and consumed once by the correct child; every #15573 authority-ordering and failure-path test remains green.
• An open popup follows a later Workstation dark↔light toggle and lands on the new palette, not merely a different class.
• The full five-beat Workstation journey remains green, including popup birth, conversion, docking, and reintegration.
• #15955 records this as a confirmed class with the native frame timestamps and repaired carrier.

Avoided Traps

• Fixed content="dark": correct for only one Workstation state and wrong for explicit light.
• content="dark light": selects from host preference, not Neo's active theme.
• prefers-color-scheme as authority: OS preference and Workstation runtime theme are independent axes.
• Styling only about:blank: the measured white frames continue after the final URL appears.
• Retheming only after child connection: permits an opposite-theme viewport frame before correction.
• Removing route staging or direct-opening the final URL: reopens the authority-less-popup race fixed by #15573.
• document.write, a synthetic boot document, or duplicated palette CSS: unnecessarily takes ownership of navigation, CSP, base URL, caching, or skin authority.
• <meta name="theme-color">: addresses browser UI, not the document canvas.
• Calling the flash a recorder artifact: it is a physical popup surface inside the live product gesture and is source-correlated.

Prior Art / Duplicate Sweep

• #15955 owns enumeration and explicitly left the full Take 17 popup path untested; this ticket is its confirmed-class repair leaf.
• #15396 / PR #15573 own staged route admission and must not regress.
• #15923 / PR #15928 moved the token bridge to the vessel viewport and added same-app post-open theme fan-out; that establishes the later-toggle authority but not the child birth carrier.
• Live title/body, latest-open, Memory Core, Knowledge Base, and A2A sweeps found no exact open duplicate.

Related: #15252, #15396, #15573, #15923, #15928, #15955.

Origin Session ID: 019f9e1e-2ef1-72c3-a04d-6bc67a531a8b

Implementation Session ID: 019fa906-0873-7e63-aa2b-2728755b3357

Retrieval hint: query_raw_memories("popup first paint carried Neo theme opposing OS preference")

Correction 2026-07-28: The fixed-dark proposal and dark-only AC were withdrawn after exact-head native evidence exposed the missing light-theme parity axis. The ticket now names Workspace.me.theme as authority and requires an opposing Neo-theme/OS-preference matrix.