fix(response-viewer): keep a path link's label in the prose font, pin its edges

Merge-time fix for #665.

- A markdown link converted to a preview link became `a.rv-path`, so its
  label ("Our incident record") took the path style: monospace, 0.92em
  and `word-break: break-all`, which split prose mid-word on a phone. The
  anchor now also carries `rv-path-link`, and
  `.rv-text a.rv-path.rv-path-link` resets font and word-break, as the
  File Viewer does for its labelled document links.
- The first new test adds `/tmp/a.json?raw=true` (pins the `?query`
  strip) and `/tmp/` (pins the trailing-slash folder check, since
  findFilePathLinks finds no folder in a bare `/tmp/`), and checks the
  new class.
- The `_linkifyFilePaths` JSDoc and docs/architecture-invariants.md say
  the function also rewrites anchors whose href is a scheme-less,
  non-`//` path, on purpose without FILE_PATH_LINK_PATTERN's root and
  extension filter.
- Mobile Guide: "a web link" in the response viewer opens a tab.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -386,7 +386,7 @@ A file path an agent prints is a link on both surfaces it can appear on, and cli
 
 **One pattern, two consumers.** `FILE_PATH_LINK_PATTERN` / `absoluteFilePathPattern()` live in `constants.js`; the xterm link provider (`registerFilePathLinkProvider`, terminal-ui.js) and the response viewer's `_linkifyFilePaths()` (app.js) both reach it through `findFilePathLinks()` (below), which builds a fresh instance per call. ⚠️ Fresh per call, never one shared object: `lastIndex` is per-object state on a `/g` regex. The pattern is anchored on a known absolute root and terminated by a known extension, so a fraction (`3/4`) or a date can't match and trailing punctuation stays out. Roots include `Users` and `mnt`, without which nothing was clickable on macOS or WSL. The linear-time guard and the "terminal-ui builds from the factory" structural check are in `test/link-provider-regex.test.ts`.
 
-**The chat linkifier walks text nodes.** `_linkifyFilePaths()` builds anchors with `createElement`/`textContent` on the rendered subtree, never by rebuilding sanitized markup as a string — the source is model output. Subtrees already inside an `<a>` are skipped (marked autolinks URLs; a nested anchor would swallow the click), and the anchor's text is the path verbatim so "copy code" still yields what the agent printed. `test/response-viewer-file-links.test.ts` pins both properties.
+**The chat linkifier walks text nodes.** `_linkifyFilePaths()` builds anchors with `createElement`/`textContent` on the rendered subtree, never by rebuilding sanitized markup as a string — the source is model output. Subtrees already inside an `<a>` are skipped (marked autolinks URLs; a nested anchor would swallow the click), and the anchor's text is the path verbatim so "copy code" still yields what the agent printed. Before the walk it also rewrites existing anchors whose href is a scheme-less, non-`//` path (Codex cites files as `[label](/abs/path.json)`, which otherwise opens as a same-origin URL) into the same `a.rv-path` shape, plus `rv-path-link` so the label keeps the prose font, on purpose without `FILE_PATH_LINK_PATTERN`'s root and extension filter: the href is a link target the agent chose. `test/response-viewer-file-links.test.ts` pins both properties and the anchor rewrite.
 
 **Out-of-workspace paths go through the attachment routes, not the file routes.** `file-content`/`file-raw` resolve against `workingDir` and 404 anything that escapes it, which is correct and unchanged — but the paths agents most often print (a `/tmp` capture, Claude's own scratchpad, another checkout) are exactly that, so clicking one used to report "File not found" for a file sitting on disk. `openFilePreview()` now detects the case (`_isExternalPreviewPath`, a string compare for ROUTING only; the real decision stays server-side) and registers the path via `POST /api/sessions/:id/attachments` first, rendering by id. ⚠️ That registration passes `notify: false`, which suppresses ONLY the `attachment:detected` broadcast — the guard, the registry entry and the by-id routes are identical either way. Without it every click also popped an attachment card announcing the file already filling the screen. ⚠️ The click is an explicit user action on the **explicit, Origin-guarded** registration route, which is why it may cross the workspace boundary at all; the passive magic-link scanner stays force-confined. A type outside `SUPPORTED_ATTACHMENT_EXTENSIONS` (`.svg`, `.bmp`) is refused with a message naming what IS previewable, rather than the registry's own policy term.
 

docs/wiki/Mobile-Guide.md

@@ -131,7 +131,7 @@ already writing in the editor.
 
 ## Tapping, links and copying
 
-- **Tap a link** in terminal output and it opens in a new tab. Same for a link in an agent's
+- **Tap a link** in terminal output and it opens in a new tab. Same for a web link in an agent's
   answer in the response viewer — it opens a tab rather than navigating the dashboard away,
   which on a phone would unload the whole session view.
 - **Tap a file path** an agent printed, or a link to one in its answer (Codex writes