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, 18 insertions, 0 deletions

diff --git a/crates/dinggerd/src/hooks.rs b/crates/dinggerd/src/hooks.rs
index 46077cf..191309a 100644
--- a/crates/dinggerd/src/hooks.rs
+++ b/crates/dinggerd/src/hooks.rs
@@ -6,6 +6,9 @@
 //! {"method":"pane.report_agent","params":{"pane_id":"%3","agent":"pi","state":"working"}}
 //! ```
 //!
+//! A report may carry the agent's session reference (`agent_session_path`
+//! or `agent_session_id`, herdr's names), which restore uses to resume it.
+//!
 //! Reports are state-change *events*: the watcher applies every one in
 //! order, so a turn that starts and finishes between two polls is still a
 //! completion, and each report wakes the watcher immediately.
@@ -40,6 +43,8 @@ struct PaneReports {
     last: Option<AgentState>,
     /// Reports not yet applied by the watcher, oldest first.
     pending: Vec<AgentState>,
+    /// The agent's latest session reference.
+    session: Option<String>,
 }
 
 fn reports() -> MutexGuard<'static, HashMap<String, PaneReports>> {
@@ -92,6 +97,10 @@ struct HookMessage {
 struct HookParams {
     pane_id: String,
     state: String,
+    #[serde(default)]
+    agent_session_path: Option<String>,
+    #[serde(default)]
+    agent_session_id: Option<String>,
 }
 
 fn handle_stream(stream: UnixStream) {
@@ -123,6 +132,10 @@ fn handle_stream(stream: UnixStream) {
             let pane = reports.entry(params.pane_id).or_default();
             pane.last = Some(state);
             pane.pending.push(state);
+            let session = params.agent_session_path.or(params.agent_session_id);
+            if let Some(session) = session.filter(|s| !s.is_empty() && !s.chars().any(char::is_control)) {
+                pane.session = Some(session);
+            }
         }
         wake();
     }
@@ -168,6 +181,11 @@ pub fn last_state(pane_id: &str) -> Option<AgentState> {
     reports().get(pane_id).and_then(|pane| pane.last)
 }
 
+/// The pane's agent session reference, if its extension reported one.
+pub fn session(pane_id: &str) -> Option<String> {
+    reports().get(pane_id).and_then(|pane| pane.session.clone())
+}
+
 /// Drop a pane's reports (the agent exited).
 pub fn drop_reports(pane_id: &str) {
     reports().remove(pane_id);