restore, step 2: resume agents, retype command lines

- the pi extension reports its session file; the daemon keeps it in the
  pane option @agent_session, and snapshots carry it. restore runs
  `pi --session <file>` in the rebuilt pane, one agent every 0.5s, then
  reports which agents run and which were interrupted mid-turn.
- other panes: the command line running in them is typed at the new
  prompt but not run. exactly as typed with the zsh hook (dingger install
  zsh: preexec/precmd keep @dingger_cmd), else the foreground program's
  exact argv from the kernel (KERN_PROCARGS2), shell-quoted.
- "at a prompt" is the pane's own shell owning the terminal's foreground
  process group, not a name check: `sh -c ...` is a running program.
- an agent or command that exits keeps its place in snapshots for 60s, so
  a shutdown that stops programs before tmux still restores them.
- typing waits for each new prompt (text typed earlier echoes twice).

e2e step 16 covers resume with a session path containing a space, the
interrupted report, an agent that exits just before the server dies, a
quoted command retyped not run, and the hook's text; dropping the grace
period, judging prompts by name, running retyped commands, or not storing
the session reference each fail it. the test's fake pi is guarded so a
real pi never starts.

1 files changed, 16 insertions, 0 deletions

diff --git a/crates/dinggerd/assets/pi/pi-agent-state.ts b/crates/dinggerd/assets/pi/pi-agent-state.ts
index df9e4e2..ff893e7 100644
--- a/crates/dinggerd/assets/pi/pi-agent-state.ts
+++ b/crates/dinggerd/assets/pi/pi-agent-state.ts
@@ -56,6 +56,19 @@ async function sendRequest(request: unknown): Promise<void> {
 
 type AgentState = "working" | "blocked" | "idle";
 
+// The session file, so `dingger restore` can resume this session with
+// `pi --session <file>`. It changes with /new, /resume, and forks.
+let sessionFile: string | undefined;
+
+function updateSessionFile(ctx: any): void {
+  try {
+    const file = ctx?.sessionManager?.getSessionFile?.();
+    sessionFile = typeof file === "string" && file.length > 0 ? file : undefined;
+  } catch {
+    sessionFile = undefined;
+  }
+}
+
 function report(state: AgentState, message?: string): Promise<void> {
   return sendRequest({
     id: `${source}:${Date.now()}:${Math.random().toString(36).slice(2)}`,
@@ -67,6 +80,7 @@ function report(state: AgentState, message?: string): Promise<void> {
       state,
       message,
       seq: Date.now() * 1000,
+      ...(sessionFile ? { agent_session_path: sessionFile } : {}),
     },
   });
 }
@@ -154,11 +168,13 @@ export default function (pi) {
     }
     // A reload can replace this extension mid-run without emitting another agent_start.
     agentActive = ctx?.isIdle?.() === false;
+    updateSessionFile(ctx);
     publishState(true);
   });
 
   pi.on("agent_start", (_event, ctx) => {
     agentActive = true;
+    updateSessionFile(ctx);
     publishState();
   });