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>

docs/architecture-invariants.md

@@ -122,6 +122,18 @@ Implementation detail extracted from `CLAUDE.md` so that file stays small enough
 
 **Attachments** (live external document references; COD-37/#119 core, COD-38/#120 previews, COD-39/#121 history): all wiring in `file-routes.ts`. **Registry** (`attachment-registry.ts`): an **in-memory** map of a stable `attachmentId` → an absolute, `realpath`-resolved, extension-allowlisted file path, so browser requests (`GET /api/sessions/:id/attachments/:attachmentId/raw`) never carry arbitrary absolute paths; `POST /api/sessions/:id/attachments` registers one. **Magic links** (`attachment-magic.ts`): parses `codeman://attach?...` out of terminal output — ⚠️ this scanner is prompt-injectable, so the scan path is **force-confined to the session workspace** (a hostile prompt could otherwise make it read arbitrary host files over SSE); emits the `attachment:detected` SSE event. Security gate is an extension **allowlist** (`isSupportedAttachmentExtension`, in the registry/magic modules), not a blocklist; a separate path layer (`config/attachment-guard.ts`) confines reads to the workspace (`attachmentConfineToWorkspace`) and blocks sensitive trees (`/root`, `/etc`). **Previews + thumbnails** (COD-38): `:attachmentId/preview` + `:attachmentId/thumbnail` (and the workspace-file equivalents `file-preview`/`file-thumbnail`) render Office docs/PDFs via external converters (`pdftoppm` / LibreOffice `soffice` / Word-COM `powershell`); `document-preview-cache.ts` is a shared disk cache (de-dups _identical_ in-flight inputs), `document-thumbnailer.ts` does best-effort first-page images, and `document-conversion-limiter.ts` is a **global converter-spawn concurrency cap** (`runWithConversionLimit`) — without it, N distinct large docs detected at once fork N multi-minute converter processes = a localhost fork-bomb-shaped resource-exhaustion vector. **History drawer** (COD-39): `session-attachment-history.ts` tracks the last `ATTACHMENT_HISTORY_LIMIT` (100) attachments per session (`Session._attachmentHistory`, persisted via `SessionState.attachmentHistory`, replayed so externals re-register on reconnect); `GET /api/sessions/:id/attachments` is the list endpoint. ⚠️ The history drawer's launcher button is desktop-only — hidden on phones (regression-guarded; see `mobile-header-buttons-policy` test). Session-local files keep using the existing workspace-scoped `file-routes` paths; the registry is only for explicit live externals. **Codex generated artifacts** (COD-166/#150, `generated-artifact-attachments.ts`): codex-mode sessions ALSO scan (ANSI-stripped) output for `Saved to: file:///…` lines and surface those files as attachment cards with a relaxed trust policy — the allow decision runs on the **realpath-resolved** path against `os.homedir()`-anchored `~/.codex` marker dirs (symlink escapes fall back to force-confinement); gated to `mode === 'codex'` only (`source` is a REQUIRED param through the listener-deps chain — a dropped arg here silently kills the feature). Image thumbnails pass through jpg/jpeg/gif/webp.
 
+### File-path links (terminal + response viewer)
+
+A file path an agent prints is a link on both surfaces it can appear on, and clicking it opens the file-preview overlay. Three things make that work and each has bitten:
+
+**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 build a fresh instance from it. ⚠️ 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.
+
+**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, and nothing here widens `SUPPORTED_ATTACHMENT_EXTENSIONS` (an out-of-workspace `.svg`/`.bmp` is refused with a message naming what IS previewable).
+
+⚠️ **The preview overlay must outrank the panel that launched it.** `.file-preview-overlay` sits at `z-index: 5100`, above the response viewer (5000) and its backdrop (4999); at its historical 2000 a path clicked in the chat opened the overlay *behind* the chat, which reads as a dead link. It stays below the toast/picker band (10000+) so a "Saved" toast still lands on top.
+
 ### Filesystem path picker
 
 **Filesystem path picker** (Link Existing "Browse" button + the extended mobile keyboard's `📁 Path` key): a lazy one-directory-at-a-time browser over `GET /api/filesystem/browse`, with `GET /api/filesystem/preview` serving the tapped file. It starts at the active session's working directory (falling back to `/mnt/d`), hides dot entries, and inserts the chosen path **without** Enter so the prompt is not submitted. The companion `⌫ All` key clears only the current unsent prompt buffer and must never emit the agent's `/clear` command.