Render Gemini streaming responses without replacing source DOM

[kangjoseph90]

Streaming currently skips parser fixes because replacing a Gemini paragraph's innerHTML removes the Text nodes its renderer owns. Removing that guard can leave stale output or append cumulative text next to the parsed prefix. Initial-disabled sessions also miss later toggle messages.

Render each supported text block in an extension-owned shadow tree while keeping its light-DOM children intact. A clipped original slot preserves native text readers; disabling switches to a plain slot, cancels queued work and restores native display. Re-enabling reads the current source, including updates made while disabled. Streaming and completed responses now share one renderer.

• Coalesce ordinary token updates in a fixed 40 ms window. Process new hosts/structural finalization before the next paint, recognize Gemini path/index metadata and inert native formula expressions, and reconcile the preview to retain unchanged text/formula nodes. Finished tokens keep the same streaming fonts/styles. Inline code includes a visible themed background, spacing, and font inside the shadow tree; native code box styles survive disabling code repair. Rediscover replaced chat containers.
• Use markdown-it's balanced inline tokens and KaTeX's DOM renderer with MathML; keep unfinished/invalid math literal and code/math opaque to other formatting. Repair punctuation-ended emphasis before Korean suffixes, preserve literal entity spellings, normalize code whitespace/backslashes, pair nested underline tags, support bracket LaTeX delimiters, and avoid matching adjacent dollar prices as formulas. Metadata-only spans can split one token.
• Preserve native visibility, opacity, and explicit inline styles. Refresh copied styles when an ancestor inside the chat changes class/style.
• Share the engine between the Chrome adapter and generated userscript, retain listeners while disabled, and propagate storage changes across tabs. Add a persistent userscript menu toggle.
• Bundle KaTeX fonts and register their font faces at document scope. Share projection stylesheets, and hide disclaimers with removable CSS instead of deleting content.
• Keep interactive/mixed-content blocks and bare td/th text native. Paragraphs/headings inside table cells remain eligible. Shadow roots cannot be detached; disabled supported hosts retain only a plain slot.

Validation: all 58 browser tests pass, including retained source identity, 500 cumulative updates, sustained streaming, 30 rapid toggles, feature/color reset, response/SPA replacement, native button handlers, layout, selection/accessibility, font loading and Trusted Types. Completion regressions verify first-frame mounting, retained inline/formula identity, and identical streaming/final fonts. Audit regressions cover Korean quoted emphasis, code backslashes/whitespace, literal entities, bracket math, nested underline with opaque content, prices, metadata-split tokens, hidden native text/math, and nested ancestor themes. An actual installed MV3 extension also passes popup/storage and initially-disabled cross-tab tests on an intercepted gemini.google.com fixture. Public-registry npm ci, generated-userscript consistency and git diff checks pass. CI runs the same suite.

Live Gemini DOM and the installed inline-code presentation were inspected. Native response-copy, virtualization, and auto-scroll remain only partially verified; automated tests do not submit prompts to live Gemini.