feat(chat): terminal chat parity for every tool; Desktop-like artifacts

- The chat over a terminal pane now covers Claude, Codex, omp, Cursor and
  Antigravity: Cursor's agent transcript and agy's step log
  (brain/<id>/.system_generated/logs/transcript_full.jsonl) are read as
  conversations; Cursor sessions are claimed by their workspace
- Replies appear as soon as they are written: the projects-tree watcher
  broadcasts `transcript_changed` (at most every 250 ms per session) and the
  chat re-reads the transcript while the terminal underneath draws
- Stop shows from the pane's own busy line (Claude/Codex `esc to interrupt`,
  agy `… esc to cancel`), or fresh output for omp/Cursor — no hooks needed
- Permission prompts read off the terminal become a card with the tool, its
  command and "Deny with a note"; Codex gets Permission mode / Model buttons
  that open its own numbered pickers, answered from the menu card
- Artifacts: cards for pages/documents/diagrams/tables/React components, a
  Preview | Code panel with versions, copy, download, save to the Artifacts
  Hub, full screen; sandboxed iframes without allow-same-origin
- Claude panes get CLAUDE_CODE_ENABLE_TODO_TOOLS=1 so the Progress panel has a
  plan; multi-question pane menus read their Next row and question tabs
- The realtime chat bridge (structured stdio, /api/chat-bridge, /ws-chat)
  from the unreleased ad9d475 is not kept

server/lib/antigravity-usage.js

@@ -17,7 +17,8 @@
  *   5 cache read.
  * The session's name and start come from its transcript
  * (`brain/<id>/.system_generated/logs/transcript_full.jsonl`, first
- * `USER_INPUT`). A file is re-read whole when its mtime (or its non-empty
+ * `USER_INPUT`), and the same file is the conversation view's
+ * (`transcriptPath`, read by `GET /api/sessions/:id/transcript`). A file is re-read whole when its mtime (or its non-empty
  * `-wal`'s) changes — they are small — and the mtime per file lives in
  * `antigravity_conversations`, so a session the user deleted stays deleted
  * until agy writes to it again. Opening read-only still lets SQLite leave an
@@ -157,6 +158,21 @@ const transcriptFiles = (id) =>
     return ["transcript_full.jsonl", "transcript.jsonl"].map((name) => path.join(dir, name));
   });
 
+/** The transcript of conversation `id` (this account's or a member's) the
+ *  conversation view reads, or null. Only a UUID names one. */
+function transcriptPath(id) {
+  if (!/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i.test(String(id || "")))
+    return null;
+  for (const file of transcriptFiles(id)) {
+    try {
+      if (fs.statSync(file).isFile()) return file;
+    } catch {
+      /* try the next name */
+    }
+  }
+  return null;
+}
+
 /** The transcript's last write, 0 when it has none. */
 function transcriptMtime(id) {
   for (const file of transcriptFiles(id)) {
@@ -531,4 +547,5 @@ module.exports = {
   readConversation,
   ingestAntigravityUsage,
   startAntigravityUsagePoll,
+  transcriptPath,
 };