Document UI release verification

TESTING.md

@@ -1,7 +1,11 @@
 # Testing Gotcha
 
-Use this checklist for every iOS release. Add checks when a new screen or
-interaction ships so the document remains the release regression suite.
+This document is the source of truth for iOS visual verification. Every UI
+change must update its relevant scenarios in the same commit. For ordinary
+commits, run the build gates and every scenario affected by the change. A
+release test means completing this entire checklist successfully on the stated
+simulators and devices; record failures as open issues and do not sign off until
+every scenario passes.
 
 ## Test record
 
@@ -141,6 +145,31 @@ xcrun simctl launch booted de.rfc1437.gotcha
       horizontal scrolling for long lines.
 - [ ] Long-press diff text and verify normal selection and copying.
 
+## Repository files
+
+- [ ] Switch a repository between **History** and **Files**. Each mode displays
+      the expected content and switching back preserves normal navigation.
+- [ ] In Files, traverse several nested folders using rows, the navigation-bar
+      Back button, and the left-edge swipe. Folder contents and titles match the
+      repository hierarchy.
+- [ ] Open representative source files in several languages, including Rust,
+      Swift, and a scripting or markup language. Keywords, strings, comments,
+      types, and punctuation use plausible language-specific highlighting.
+- [ ] Open a source file containing a line wider than the screen. It does not
+      word-wrap; horizontal dragging pans smoothly across the complete line
+      without blank, black, clipped, delayed, or jumping text. Vertical
+      scrolling, selection, and copying still work.
+- [ ] Open Markdown files using the supported extensions (`.md`, `.markdown`,
+      `.mdown`, and `.mkd`). **Preview** is selected by default and renders
+      headings, paragraphs, emphasis, links, lists, task lists, blockquotes,
+      fenced code blocks, tables, and thematic rules as structured content.
+- [ ] Switch a Markdown file from **Preview** to **Source**. The literal Markdown
+      is syntax-highlighted, selectable, does not word-wrap, and scrolls
+      horizontally for long lines. Switch back and verify the rendered preview
+      is restored without stale or overlapping content.
+- [ ] Open representative image, PDF, audio, and video files. Each uses the
+      native preview appropriate to its media type and returns cleanly to Files.
+
 ## Pull requests
 
 - [ ] The list defaults to the saved Open/Closed filter.
@@ -184,4 +213,4 @@ xcrun simctl launch booted de.rfc1437.gotcha
 - [ ] All build gates passed.
 - [ ] Fresh-install and upgrade passes completed.
 - [ ] Every supported iOS version and required device class completed.
-- [ ] Failures are linked in the test record; release blockers are resolved.
+- [ ] Every scenario passed; any discovered failures were resolved and retested.