chat urls: a group is a path, a session decides its own directory

the chat group moves from ?cwd= to a path suffix behind a g/ discriminator
(/chat/g/home/me/project), and a session url carries no group at all.

the real fix is not the spelling. a session's working directory was read back
off the query string to decide where the agent executes, so the address bar was
the authority on where code runs. a pasted or refreshed /chat/<id> arrives with
no ?cwd= at all, so a turn sent before the resolve landed ran in the default
general_chat_sessions dir instead of the project; and a hand-edited ?cwd= could
name a group the session doesn't belong to, with nothing to reconcile them.

loadClaudeSessionById already resolves a session's cwd from the id alone, so the
id is the only source of truth there. it now travels on SelectedSession.cwd,
which is what the composer reads. the url can no longer contradict it.

the vocabulary lives in apps/ChatHistory/chat-routes.ts so a link built in a
panel and one built in a screen cannot drift.

also: startAgentRun no longer returns a literal chatUrl — it returns cwd and
AgentRunnerModal builds the link, so the server holds no copy of the frontend
url shape. and the post-turn permalink strips a stale ?cwd= instead of carrying
it forward onto the new session's url.

walkthrough doc gains item 13.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/api/chat/claude-sessions.ts

@@ -255,10 +255,35 @@ export function loadClaudeSessionById(email: string, sessionId: string): ClaudeS
   return null;
 }
 
+/**
+ * The transcript file for a session: in the named group if it is there, otherwise wherever it actually
+ * is. The caller's cwd is a hint, not an authority — a session's group is a property of the session,
+ * and the two disagree routinely (the list is showing one group while you act on a row from another,
+ * or a deep link hasn't resolved its group yet). Reads have always fallen back like this; writes did
+ * not, so delete and rename returned "not found" for a session that was plainly on screen.
+ */
+function findTranscript(email: string, cwd: string, sessionId: string): string | null {
+  const preferred = join(claudeProjectsDir(email), projectSlug(cwd), `${sessionId}.jsonl`);
+  if (existsSync(preferred)) return preferred;
+
+  const projectsDir = claudeProjectsDir(email);
+  let slugs: string[];
+  try {
+    slugs = readdirSync(projectsDir);
+  } catch {
+    return null;
+  }
+  for (const slug of slugs) {
+    const filePath = join(projectsDir, slug, `${sessionId}.jsonl`);
+    if (existsSync(filePath)) return filePath;
+  }
+  return null;
+}
+
 /** Delete a session by removing its transcript file. Returns false if it didn't exist. */
 export function deleteClaudeSession(email: string, cwd: string, sessionId: string): boolean {
-  const filePath = join(claudeProjectsDir(email), projectSlug(cwd), `${sessionId}.jsonl`);
-  if (!existsSync(filePath)) return false;
+  const filePath = findTranscript(email, cwd, sessionId);
+  if (!filePath) return false;
   rmSync(filePath);
   return true;
 }
@@ -269,8 +294,8 @@ export function deleteClaudeSession(email: string, cwd: string, sessionId: strin
  * timestamp is written so the rename doesn't reorder the list.
  */
 export function renameClaudeSession(email: string, cwd: string, sessionId: string, title: string): boolean {
-  const filePath = join(claudeProjectsDir(email), projectSlug(cwd), `${sessionId}.jsonl`);
-  if (!existsSync(filePath)) return false;
+  const filePath = findTranscript(email, cwd, sessionId);
+  if (!filePath) return false;
 
   // Attach the summary to the transcript's tip (the last entry carrying a uuid).
   let leafUuid = sessionId;