feat(maestro): add acp_session_id to the session sidecar (#134)

A Structured session's adapter hands back an ACP session id from
session/new; a respawn will pass it to session/load (#135). This is a
new field rather than #161's agent_session_id: that one is the Claude
Code conversation id the activity hook reports and `claude --resume`
takes, minted by Claude Code itself. The ACP id is minted by the
adapter, only exists for Structured sessions, and is what the adapter
takes back. Overloading one field with two ids from two processes
would leave a respawn unable to tell which kind it holds.

crates/maestro-cli/src/sessions.rs

@@ -254,6 +254,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 

crates/maestro-daemon/src/session.rs

@@ -478,6 +478,7 @@ impl SessionManager {
             // fresh tree has nothing in the way anyway.
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
             view: req.view,
         };
 
@@ -684,6 +685,7 @@ impl SessionManager {
                     current_cwd: None,
                     blocked_work: None,
                     last_focused_at: None,
+                    acp_session_id: None,
                     // Unknown on adoption without a sidecar; matches every
                     // other field's forward-compat default.
                     view: maestro_protocol::SessionView::Terminal,

crates/maestro-daemon/tests/sidecar.rs

@@ -32,6 +32,7 @@ fn sample(id: Uuid) -> Session {
         current_cwd: Some(PathBuf::from("/tmp/work/crates")),
         blocked_work: None,
         last_focused_at: None,
+        acp_session_id: None,
         view: SessionView::Terminal,
     }
 }

crates/maestro-protocol/src/display.rs

@@ -285,6 +285,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 

crates/maestro-protocol/src/lib.rs

@@ -123,6 +123,15 @@ pub struct Session {
     /// daemon that predates the field keeps working untouched.
     #[serde(default)]
     pub view: SessionView,
+    /// The ACP session id the `claude-code-acp` adapter handed back from
+    /// `session/new` (#134). Only a [`SessionView::Structured`] session has
+    /// one, and only once its handshake succeeded; a later respawn passes it
+    /// to `session/load` so the conversation continues (#135). Distinct from
+    /// the hook-reported Claude Code conversation id (#161): that one is what
+    /// `claude --resume` takes, this one is what the ACP adapter takes, and
+    /// the two are minted by different processes with different lifetimes.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub acp_session_id: Option<String>,
 }
 
 /// A session's process shape (#133): a plain terminal, or a structured agent
@@ -886,6 +895,7 @@ mod tests {
             blocked_work: None,
             last_focused_at: None,
             view: SessionView::Terminal,
+            acp_session_id: None,
         }
     }
 
@@ -1134,6 +1144,29 @@ mod tests {
         assert_eq!(structured, round_trip(&structured));
     }
 
+    #[test]
+    fn acp_session_id_defaults_to_none_and_round_trips() {
+        // A payload from before #134 carries no `acp_session_id`; it must
+        // read as `None`, stay off the wire while unset, and round-trip
+        // once the adapter has handed one back.
+        let json = serde_json::json!({
+            "id": Uuid::from_u128(1),
+            "cwd": "/tmp",
+            "command": "bash",
+            "status": "Running",
+            "created_at": "2026-05-24T12:00:00Z"
+        });
+        let s: Session = serde_json::from_value(json).unwrap();
+        assert_eq!(s.acp_session_id, None);
+        let serialized = serde_json::to_value(&s).unwrap();
+        assert!(serialized.get("acp_session_id").is_none());
+
+        let mut structured = sample_session();
+        structured.view = SessionView::Structured;
+        structured.acp_session_id = Some("sess_01HZX".into());
+        assert_eq!(structured, round_trip(&structured));
+    }
+
     /// A client that predates the new/existing discriminator sends no
     /// `create_branch`; the daemon must read that as "create a new branch" —
     /// exactly what every payload meant before the field existed (#56).

crates/maestro-testing/src/lib.rs

@@ -48,6 +48,7 @@ pub fn session(id: Uuid, cwd: &str, command: &str) -> Session {
         current_cwd: None,
         blocked_work: None,
         last_focused_at: None,
+        acp_session_id: None,
     }
 }
 

crates/maestro-tui/src/app.rs

@@ -1899,6 +1899,7 @@ mod tests {
                     current_cwd: None,
                     blocked_work: None,
                     last_focused_at: None,
+                    acp_session_id: None,
                 })
                 .collect(),
         });
@@ -2081,6 +2082,7 @@ mod tests {
                 current_cwd: None,
                 blocked_work: None,
                 last_focused_at: None,
+                acp_session_id: None,
             }],
         });
         app.dispatch(Action::SidebarNext);
@@ -2109,6 +2111,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 
@@ -3219,6 +3222,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: focused,
+            acp_session_id: None,
         };
         let older = Utc::now() - chrono::Duration::seconds(60);
         app.catalog.apply_event(CatalogEvent::Snapshot {
@@ -3498,6 +3502,7 @@ mod tests {
                 current_cwd: None,
                 blocked_work: None,
                 last_focused_at: None,
+                acp_session_id: None,
             }],
         });
         app.dispatch(Action::KillHighlighted);
@@ -3534,6 +3539,7 @@ mod tests {
                 current_cwd: None,
                 blocked_work: None,
                 last_focused_at: None,
+                acp_session_id: None,
             }],
         });
     }

crates/maestro-tui/src/catalog.rs

@@ -224,6 +224,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 

crates/maestro-tui/src/command_bar.rs

@@ -810,6 +810,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 

crates/maestro-tui/src/sidebar.rs

@@ -501,6 +501,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         }
     }
 
@@ -1268,6 +1269,7 @@ mod tests {
             current_cwd: None,
             blocked_work: None,
             last_focused_at: None,
+            acp_session_id: None,
         };
         let sb = Sidebar {
             sessions: vec![s],