feat: show auto-generated session names in resume picker

- Pino's resume picker now prefers pi session_info name (if set by
  session-namer) over the preview text. Last session_info wins on rename.
- Fallback: preview (first message) or timestamp if no name is set.
- Verified with 6-test suite (new test covers name precedence).

Author: leduckhc

server/src/pi-sessions.test.ts

@@ -67,6 +67,55 @@ test("listPiSessions parses headers, filters by cwd, sorts by mtime desc", () =>
   }
 });
 
+test("listPiSessions prefers the session_info name (last wins), else preview", () => {
+  const agentDir = mkdtempSync(join(tmpdir(), "pino-agent-"));
+  try {
+    const cwd = "/work/named";
+    const dir = piSessionsDir(cwd, agentDir);
+    mkdirSync(dir, { recursive: true });
+
+    // Named session: two session_info entries → the LAST one wins for the label,
+    // while `preview` still reflects the first user message.
+    const named = join(dir, "2026-01-01T00-00-00-000Z_named.jsonl");
+    writeFileSync(
+      named,
+      [
+        JSON.stringify({ type: "session", version: 3, id: "named", timestamp: "2026-01-01T00:00:00.000Z", cwd }),
+        JSON.stringify({ type: "message", message: { role: "user", content: [{ type: "text", text: "add rate limiting to my express api" }] } }),
+        JSON.stringify({ type: "session_info", id: "si1", timestamp: "2026-01-01T00:01:00.000Z", name: "Rough First Name" }),
+        JSON.stringify({ type: "message", message: { role: "assistant", content: [{ type: "text", text: "sure" }] } }),
+        JSON.stringify({ type: "session_info", id: "si2", timestamp: "2026-01-01T00:02:00.000Z", name: "Add Rate Limiting to Express API" }),
+      ].join("\n") + "\n",
+    );
+
+    // Unnamed session: no session_info → falls back to the first user message.
+    const unnamed = join(dir, "2026-01-01T00-00-00-000Z_unnamed.jsonl");
+    writeFileSync(
+      unnamed,
+      [
+        JSON.stringify({ type: "session", version: 3, id: "unnamed", timestamp: "2026-01-01T00:00:00.000Z", cwd }),
+        JSON.stringify({ type: "message", message: { role: "user", content: [{ type: "text", text: "just the first message" }] } }),
+      ].join("\n") + "\n",
+    );
+
+    utimesSync(named, new Date(2000), new Date(2000));
+    utimesSync(unnamed, new Date(1000), new Date(1000));
+
+    const list = listPiSessions(cwd, agentDir);
+    const byId = Object.fromEntries(list.map((m) => [m.piSessionId, m]));
+
+    // Named: label is the latest session_info name; preview keeps the 1st message.
+    assert.equal(byId.named.name, "Add Rate Limiting to Express API");
+    assert.equal(byId.named.preview, "add rate limiting to my express api");
+
+    // Unnamed: label falls back to the first user message.
+    assert.equal(byId.unnamed.name, "just the first message");
+    assert.equal(byId.unnamed.preview, "just the first message");
+  } finally {
+    rmSync(agentDir, { recursive: true, force: true });
+  }
+});
+
 test("listPiSessions returns [] when the slug dir is absent", () => {
   const agentDir = mkdtempSync(join(tmpdir(), "pino-agent-"));
   try {

server/src/pi-sessions.ts

@@ -25,7 +25,7 @@ export interface PiSessionMeta {
   piSessionId: string;
   /** Full path to the .jsonl transcript (server-internal; harmless to app). */
   path: string;
-  /** Human label — first user message, else the timestamp. */
+  /** Human label — auto-generated name (if any), else first user message, else timestamp. */
   name: string;
   /** First user message, truncated. */
   preview: string;
@@ -102,9 +102,10 @@ export function listPiSessions(cwd: string, agentDir: string = realAgentDir()):
 }
 
 /** Build metadata (preview / count / mtime) for a single transcript. */
-function summarize(path: string, header: Header): PiSessionMeta {
+export function summarize(path: string, header: Header): PiSessionMeta {
   let preview = "";
   let messageCount = 0;
+  let autoGeneratedName = ""; // pi session-namer auto-generated name
   try {
     for (const line of readFileSync(path, "utf8").split("\n")) {
       if (!line.trim()) continue;
@@ -121,6 +122,10 @@ function summarize(path: string, header: Header): PiSessionMeta {
           preview = extractText(o.message?.content).slice(0, PREVIEW_MAX);
         }
       }
+      // Capture the most recent auto-generated name from session_info entries.
+      if (o?.type === "session_info" && typeof o?.name === "string" && o.name) {
+        autoGeneratedName = o.name;
+      }
     }
   } catch {
     // Best-effort; a partially-read file still yields a usable meta.
@@ -133,10 +138,13 @@ function summarize(path: string, header: Header): PiSessionMeta {
     lastActivityAt = Date.parse(header.timestamp) || 0;
   }
 
+  // Prefer auto-generated name, then user's first message, then timestamp.
+  const name = autoGeneratedName || preview || header.timestamp;
+
   return {
     piSessionId: header.id,
     path,
-    name: preview || header.timestamp,
+    name,
     preview,
     messageCount,
     lastActivityAt,