diff --git a/crates/maestro-cli/src/sessions.rs b/crates/maestro-cli/src/sessions.rs
index b5a8652..21296a5 100644
--- a/crates/maestro-cli/src/sessions.rs
+++ b/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,
         }
     }
 
diff --git a/crates/maestro-daemon/src/session.rs b/crates/maestro-daemon/src/session.rs
index 7d17d38..e8f6a4e 100644
--- a/crates/maestro-daemon/src/session.rs
+++ b/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,
diff --git a/crates/maestro-daemon/tests/sidecar.rs b/crates/maestro-daemon/tests/sidecar.rs
index 4aa7ff2..f942e2d 100644
--- a/crates/maestro-daemon/tests/sidecar.rs
+++ b/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,
     }
 }
diff --git a/crates/maestro-protocol/src/display.rs b/crates/maestro-protocol/src/display.rs
index f7d38b8..d535c69 100644
--- a/crates/maestro-protocol/src/display.rs
+++ b/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,
         }
     }
 
diff --git a/crates/maestro-protocol/src/lib.rs b/crates/maestro-protocol/src/lib.rs
index ead867b..ad38b97 100644
--- a/crates/maestro-protocol/src/lib.rs
+++ b/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).
diff --git a/crates/maestro-testing/src/lib.rs b/crates/maestro-testing/src/lib.rs
index 35c233d..30c8535 100644
--- a/crates/maestro-testing/src/lib.rs
+++ b/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,
     }
 }
 
diff --git a/crates/maestro-tui/src/app.rs b/crates/maestro-tui/src/app.rs
index b52d4fd..d62a605 100644
--- a/crates/maestro-tui/src/app.rs
+++ b/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,
             }],
         });
     }
diff --git a/crates/maestro-tui/src/catalog.rs b/crates/maestro-tui/src/catalog.rs
index 9a78c84..4a42e4f 100644
--- a/crates/maestro-tui/src/catalog.rs
+++ b/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,
         }
     }
 
diff --git a/crates/maestro-tui/src/command_bar.rs b/crates/maestro-tui/src/command_bar.rs
index 883e3d1..095dee7 100644
--- a/crates/maestro-tui/src/command_bar.rs
+++ b/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,
         }
     }
 
diff --git a/crates/maestro-tui/src/sidebar.rs b/crates/maestro-tui/src/sidebar.rs
index c22d3aa..c91e94f 100644
--- a/crates/maestro-tui/src/sidebar.rs
+++ b/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],
diff --git a/web/src/types.ts b/web/src/types.ts
index 091883e..3870c7d 100644
--- a/web/src/types.ts
+++ b/web/src/types.ts
@@ -56,6 +56,10 @@ export interface Session {
    * how the command bar's empty query sorts a never-focused session after every
    * session that has one (`docs/COMMAND-BAR.md`). */
   last_focused_at?: IsoTimestamp | null;
+  /** The ACP session id the `claude-code-acp` adapter returned from
+   * `session/new` (#134). Only a `Structured` session whose handshake
+   * succeeded has one; a respawn passes it to `session/load` (#135). */
+  acp_session_id?: string | null;
 }
 
 /** A session's daemon-created worktree (`SessionWorktree` on the wire). */