Start a stopped session's process for a command too

Same reasoning as the message path a commit ago, and the same objection
to leaving it out: a command is something somebody asked the session to
do, and answering "its process has exited" hands back the work of
starting one. `/compact` on a stopped session is the case that shows it
-- what is being asked for is exactly what a stopped session needs
before it is useful again.

`POST /sessions/{id}/command` and `/compact` now go through
`SessionManager::run_command`. A rename is deliberately not one of them:
it is persisted and listed whether or not a process ever hears about it,
so starting a CLI to tell it a name would be spending a resume on
nothing. It stays a forward to a process that happens to be there.

A command needs one thing a message did not. `Commands::submit` refuses
on `Exited`, and a driver that has just started a process announces
`Idle` through the sink rather than writing it -- so a command judged
against the session's own status would be refused by the word the start
had just replaced, in a window narrow enough that only a test reliably
hits it. `start_if_exited` returning `Exited` is what says a process was
started, so the status the command is judged against comes from there
rather than from a re-read the pump may not have caught up with. The
test fails without it.

`LiveSession::compact` went with this: `/compact` the route and
"/compact" the typed command were two ways to the same command, and now
there is one.

Verified over the API against a stand-in CLI: with the session reporting
`exited`, both `/clear` and `POST /compact` started the process and were
delivered -- transcript order `idle`, `commandSent`, `running`, `idle`,
with no "this session's process has exited" anywhere.

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

server/src/session/mod.rs

@@ -399,13 +399,6 @@ impl LiveSession {
         self.driver().detach();
     }
 
-    /// Compacts at the next boundary. Through the command queue like
-    /// every other instruction to the session, so pressing it during a
-    /// turn holds rather than writing into that turn.
-    pub fn compact(&self) {
-        self.run_command(SessionCommand::Compact);
-    }
-
     pub fn subscribe(&self) -> broadcast::Receiver<SeqEvent> {
         self.events.subscribe()
     }
@@ -1150,6 +1143,42 @@ impl SessionManager {
         Ok(())
     }
 
+    /// Runs one of the session's own commands, starting its process first
+    /// if that session has none.
+    ///
+    /// The same reasoning as [`SessionManager::send_message`], and for the
+    /// same reason it is not left to each caller: a command is something
+    /// somebody asked the session to do, and answering "its process has
+    /// exited" hands back the work of starting one. `/compact` on a
+    /// stopped session is the case that shows it -- the thing being asked
+    /// for is exactly what a stopped session needs before it is useful
+    /// again.
+    ///
+    /// Renaming is deliberately not here. It is persisted and listed
+    /// whether or not a process ever hears about it, so starting a CLI to
+    /// tell it a name would be spending a resume on nothing -- see
+    /// [`SessionManager::rename_session`], which forwards it to a process
+    /// that happens to be there.
+    pub fn run_command(&self, id: &str, command: SessionCommand) -> Result<()> {
+        // Judged against the status *after* the start, not the one that
+        // caused it. A driver that has just started a process announces
+        // `idle` through the sink and the pump may not have recorded it
+        // yet, so reading the session's own status here would refuse the
+        // command the start was for -- `Commands::submit` refuses on
+        // `Exited`, which is exactly the word that has just stopped being
+        // true. `start_if_exited` returning `Exited` is what says a process
+        // was started; anything else is a status nothing has invalidated.
+        let status = match self.start_if_exited(id)? {
+            SessionStatus::Exited => SessionStatus::Idle,
+            found => found,
+        };
+        self.session(id)
+            .with_context(|| format!("no session {id}"))?
+            .commands
+            .submit(command, status);
+        Ok(())
+    }
+
     /// Starts a process for the session if it is known to have exited, and
     /// reports what the session was found to be doing either way. `Exited`
     /// is therefore the one returned value that means something was started.
@@ -2612,16 +2641,22 @@ mod tests {
         ));
     }
 
-    /// Sending is an instruction that means "now", so it does not answer
-    /// that the session's process has gone -- it starts one and delivers
-    /// the message to it.
+    /// A message and a command both mean "now", so neither answers that the
+    /// session's process has gone -- they start one and go to it.
     ///
     /// Refusing was the old behaviour and it was work handed back: read the
-    /// status word, find the other button, press it, type the message
-    /// again. `--resume` puts the new process on the same conversation, so
-    /// the message it reads is the one that was typed.
+    /// status word, find the other button, press it, type the thing again.
+    /// `--resume` puts the new process on the same conversation, so what it
+    /// reads is what was typed.
+    ///
+    /// Both halves in one test because they are one rule. A command is the
+    /// half that can fail on its own: `Commands::submit` refuses on
+    /// `Exited`, and the start it has just been given announces `Idle`
+    /// through the sink rather than writing it -- so a command judged
+    /// against the session's own status would be refused by the word the
+    /// start replaced, in a window a test is the only thing likely to hit.
     #[tokio::test]
-    async fn a_message_starts_the_process_a_stopped_session_has_not_got() {
+    async fn an_instruction_starts_the_process_a_stopped_session_has_not_got() {
         let dir = tempfile::tempdir().expect("tempdir");
         let config_path = dir.path().join("config.ron");
         let data_dir = dir.path().join("sessions");
@@ -2657,6 +2692,25 @@ mod tests {
         // delivered to a session still reporting `exited` is one the phone
         // draws under a Start button.
         assert_ne!(manager.sessions()[0].status, SessionStatus::Exited);
+
+        let _ = session.sink.send(Event::Status {
+            state: SessionStatus::Exited,
+        });
+        collect_until(&mut rx, |event| {
+            matches!(
+                event,
+                Event::Status {
+                    state: SessionStatus::Exited
+                }
+            )
+        })
+        .await;
+
+        manager
+            .run_command(&info.id, SessionCommand::Clear)
+            .expect("clear a stopped session");
+        collect_until(&mut rx, |event| matches!(event, Event::Cleared)).await;
+        assert_ne!(manager.sessions()[0].status, SessionStatus::Exited);
     }
 
     /// The status is a claim about a process, and the process record is