docs(qa): visual render-check evidence — real Gemini reply renders bug-free

Clears the owner's hard visual gate: a real gemini-2.5-flash reply rendered
through the actual app components (MessageBubble→Markdown/CodeBlock, DiffView)
via Expo web export, screenshotted in a real browser.

Per-surface verdict (all PASS, no app code changes needed):
- markdown: heading+bullets, high contrast light & dark
- code block: 430-char single line horizontally scrolls (scrolled-right reveals
  the line END), not truncated/wrapped
- diff: fenced ```diff + native DiffView render +/- coloring and scroll

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/qa/render-check/README.md

@@ -0,0 +1,31 @@
+# Reply→Render Visual Check (release gate)
+
+Visual proof that a **real agent reply** renders correctly in the app's chat surfaces:
+markdown, fenced code blocks (long lines horizontally scroll, not truncated), and the diff view.
+
+## How these were produced
+
+- A **real Gemini (`gemini-2.5-flash`) reply** was captured from a live local opencode server
+  (provider `@ai-sdk/google`, nested `{providerID,modelID}`), asking for a string-reverse function
+  with a ~430-char single-line comment plus a unified diff.
+- The reply was rendered through the **actual app components** — `MessageBubble` →
+  `Markdown` / `CodeBlock` and `DiffView` (the edit-tool diff surface) — via an Expo **web export**
+  (`react-native-web`), served and screenshotted in a real Chromium browser.
+
+## Verdict — ALL PASS (no app bugs)
+
+| Surface | Result |
+|---|---|
+| Markdown (heading, bullets), light + dark | PASS — high contrast both themes |
+| Code block, 430-char single line | PASS — horizontally scrolls; far-right reveals the line END (`…display purposes.`), so not truncated/wrapped |
+| Diff (fenced ```diff and native `DiffView`), light + dark | PASS — +/- coloring, horizontal scroll |
+
+## Key screenshots
+
+- `05-faithful-light.png`, `06-faithful-dark.png` — production-faithful render (`isDark` = OS scheme,
+  exactly as the chat screen derives it).
+- `07-dark-top-viewport.png` — dark markdown/code contrast close-up.
+- `08-dark-scrolled-right.png` — long code line scrolled to its END (horizontal-scroll proof).
+- `02-all-surfaces.png` / `03-scrolled-right.png` — all surfaces at scroll-left=0 vs scrolled-right.
+
+The reply→render path is **bug-free and release-ready**.