fix(files): open file paths agents print, from the terminal and the chat

A path an agent prints was already underlined in the terminal, but clicking
one opened the preview overlay on "File not found": file-content/file-raw
resolve against the session workingDir and refuse anything outside it, and the
paths agents print most (a /tmp capture, Claude's own scratchpad, another
checkout) are outside it by definition. In the response viewer those paths were
not links at all.

- openFilePreview() detects an out-of-workspace path and registers it through
  POST /api/sessions/:id/attachments first, rendering by attachment id. That is
  the surface built for live external files, so the server-side guard is
  unchanged: secret trees blocked, symlinks resolved, extension allowlist. The
  workspace routes keep refusing escapes exactly as before.
- New optional `notify` field on that route. `notify: false` suppresses only the
  attachment:detected broadcast, so a click does not also pop a card announcing
  the file already filling the screen. Default stays true for the CLI and
  publish callers.
- _linkifyFilePaths() links paths in rendered response-viewer markdown. It walks
  text nodes and builds anchors with DOM APIs (the source is model output; never
  a string rebuild of sanitized markup), skips subtrees already inside an <a>,
  and keeps the message text byte-identical so copy-code is unaffected.
- One path pattern in constants.js now feeds both the xterm link provider and
  the chat linkifier, a fresh instance per call since lastIndex is per-object
  state. It picks up /Users and /mnt roots (nothing was clickable on macOS or
  WSL), plus docx/pptx and video/audio extensions.
- .file-preview-overlay moves to z-index 5100, above the response viewer at
  5000. At its old 2000 a path clicked in the chat opened the overlay behind the
  panel it was launched from.

Verified end to end on an isolated instance, desktop and phone viewport: real
clicks in the terminal and the chat both render the image, external md and pdf
render, /etc/hosts is still refused, workspace previews unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/web/public/constants.js

@@ -893,6 +893,45 @@ function computeRewriteScrollLine(input) {
   return Math.max(0, (input?.baseY || 0) - linesFromBottom);
 }
 
+/**
+ * Absolute file paths in agent output, as ONE pattern with two consumers: the
+ * xterm link provider (terminal-ui.js) and the response viewer's markdown
+ * linkifier (app.js). They used to be able to drift, and a path that is
+ * clickable in the terminal but inert in the chat reads as a bug, not a policy.
+ *
+ * Anchored on a known absolute root (so an ordinary fraction or a date can
+ * never match) and terminated by a known extension (so the end of the path is
+ * unambiguous — a trailing `)` or `.` after the extension stays out). Longer
+ * extensions come first in each family (`tsx|ts`), so the trailing `\b` cannot
+ * be satisfied by the shorter branch mid-word.
+ *
+ * ⚠ Consumers must never share one instance: `lastIndex` is per-object state on
+ * a `/g` regex, so {@link absoluteFilePathPattern} mints a fresh one per call.
+ */
+const FILE_PATH_LINK_PATTERN =
+  /(\/(?:home|Users|tmp|var|private|etc|opt|mnt|srv|media|data|workspace)\/[^\s"'<>|;&\n\x00-\x1f]*\.(?:log|txt|json|md|ya?ml|csv|xml|sh|py|tsx|ts|jsx|js|mjs|cjs|css|html|toml|ini|sql|png|jpe?g|gif|webp|bmp|svg|pdf|docx|pptx|mp4|webm|mov|mp3|wav))\b/g;
+
+/** A fresh, zero-state instance of {@link FILE_PATH_LINK_PATTERN}. */
+function absoluteFilePathPattern() {
+  return new RegExp(FILE_PATH_LINK_PATTERN.source, 'g');
+}
+
+/**
+ * Extensions the file-preview overlay renders itself. Everything else a link
+ * points at goes to the tail/log viewer, which is the right home for a growing
+ * text file and the wrong one for bytes (tailing a PNG shows binary noise).
+ */
+const FILE_PREVIEW_EXTENSIONS = new Set(
+  ('png jpg jpeg gif webp bmp svg pdf docx pptx mp4 webm mov mp3 wav').split(' ')
+);
+
+/** Whether a path's extension is one {@link FILE_PREVIEW_EXTENSIONS} covers. */
+function previewsInFileViewer(filePath) {
+  const ext = String(filePath || '').split('.').pop().toLowerCase();
+  return FILE_PREVIEW_EXTENSIONS.has(ext);
+}
+
 if (typeof window !== 'undefined') {
   window.CodemanHistoryFormat = { formatHistoryBytes, computeHistoryTruncationNotice, computeRewriteScrollLine };
+  window.CodemanFilePaths = { absoluteFilePathPattern, previewsInFileViewer, FILE_PREVIEW_EXTENSIONS };
 }