pi: the session name in herdr's Agent sidebar

herdr labels every pi pane "pi", so with several open the rows cannot be told
apart. herdr 0.9.3's socket API has pane.report_metadata, whose display_agent
replaces that label without touching lifecycle state; this reports the session
name there on start and on every rename, auto-named titles included.

Interactive sessions only: a pi -p or subagent run from inside a pane inherits
its HERDR_* variables and would otherwise rename the pane after itself. Checked
against a fake herdr socket: a print-mode run sends nothing, while the socket
accepted a control message. Outside herdr it returns at once. The pi APIs it
uses -- ctx.mode "tui", getSessionName, session_info_changed's name -- are as
in pi 1.0.0, and link/pi.sh links it in like any tracked extension.

From change request e053eb.

1 files changed, 84 insertions, 0 deletions

diff --git a/config/pi/extensions/herdr-session-name.ts b/config/pi/extensions/herdr-session-name.ts
new file mode 100644
index 0000000..63663f1
--- /dev/null
+++ b/config/pi/extensions/herdr-session-name.ts
@@ -0,0 +1,84 @@
+// Shows the pi session name in herdr's (or tmuxrdr's) Agent sidebar, in place of
+// the "pi" label.
+//
+// herdr's own pi integration (herdr-agent-state.ts, which herdr installs and
+// overwrites) reports lifecycle state only. This sits beside it and reports
+// display-only pane metadata: `display_agent` replaces the `agent` token in
+// sidebar rows. `agent: "pi"` guards it, so it stops applying once the pane no
+// longer runs pi. With no session name, the label is cleared back to "pi".
+//
+// Reported on session start (including /resume, /new and reloads) and whenever
+// the name changes (/name, --name, or an extension's pi.setSessionName()).
+// TUI sessions only: print, JSON and RPC runs launched from inside a pane (a
+// review panel, a subagent) inherit the pane's HERDR_* variables and would
+// otherwise rename the pane after themselves.
+//
+// API: pane.report_metadata, herdr socket API (herdr 0.9.3).
+
+import net from "node:net";
+
+const socketPath = process.env.HERDR_SOCKET_PATH;
+const paneId = process.env.HERDR_PANE_ID;
+const source = "user:pi-session-name";
+
+function enabled(): boolean {
+  return process.env.HERDR_ENV === "1" && !!socketPath && !!paneId;
+}
+
+function send(request: unknown, timeoutMs = 1000): Promise<void> {
+  return new Promise((resolve) => {
+    const endpoint =
+      process.platform === "win32" ? `\\\\.\\pipe\\${socketPath}` : socketPath!;
+    const socket = net.createConnection(endpoint);
+    const finish = () => {
+      clearTimeout(timer);
+      socket.destroy();
+      resolve();
+    };
+    const timer = setTimeout(finish, timeoutMs);
+    timer.unref?.();
+    socket.on("error", finish);
+    socket.on("end", finish);
+    socket.on("data", finish);
+    socket.on("connect", () => socket.write(`${JSON.stringify(request)}\n`));
+  });
+}
+
+let seq = Date.now() * 1000;
+
+function report(name: string | undefined): Promise<void> {
+  const label = name?.trim();
+  seq += 1;
+  return send({
+    id: `${source}:${seq}`,
+    method: "pane.report_metadata",
+    params: {
+      pane_id: paneId,
+      source,
+      agent: "pi",
+      seq,
+      ...(label ? { display_agent: label } : { clear_display_agent: true }),
+    },
+  });
+}
+
+export default function (pi: any) {
+  if (!enabled()) {
+    return;
+  }
+
+  let active = false;
+
+  pi.on("session_start", async (_event: unknown, ctx: any) => {
+    active = ctx?.mode === "tui";
+    if (active) {
+      await report(pi.getSessionName());
+    }
+  });
+
+  pi.on("session_info_changed", async (event: { name?: string }) => {
+    if (active) {
+      await report(event?.name);
+    }
+  });
+}