diff --git a/crates/maestro-hooks/src/lib.rs b/crates/maestro-hooks/src/lib.rs
index 1b70b11..fcd4359 100644
--- a/crates/maestro-hooks/src/lib.rs
+++ b/crates/maestro-hooks/src/lib.rs
@@ -27,8 +27,11 @@ pub const SCRIPT_FILE_NAME: &str = "maestro-claude-hook.sh";
 /// Claude Code hook event → `ActivityState` spelling posted to the daemon.
 ///
 /// `PreToolUse` is what makes a session `Active` *during* a long tool call —
-/// `PostToolUse` alone only fires once it ends (#114).
-pub const HOOK_EVENTS: [(&str, &str); 4] = [
+/// `PostToolUse` alone only fires once it ends (#114). `StopFailure` is
+/// Claude Code's own name for "the turn ended on an API error"; there is no
+/// failure signal in `Stop` or `SessionEnd` payloads, so those never report
+/// `Error`.
+pub const HOOK_EVENTS: [(&str, &str); 5] = [
     // Tool starting: the agent is demonstrably producing work, even if the
     // tool itself runs for minutes.
     ("PreToolUse", "Active"),
@@ -38,6 +41,9 @@ pub const HOOK_EVENTS: [(&str, &str); 4] = [
     ("Notification", "AwaitingInput"),
     // Turn ended: waiting on the user again.
     ("Stop", "AwaitingInput"),
+    // Turn ended on an API error; the payload's `error` field is forwarded
+    // as the report's `detail` (#114).
+    ("StopFailure", "Error"),
 ];
 
 /// The shipped hook script. POSIX sh so any `/bin/sh` works.
@@ -49,14 +55,23 @@ pub const HOOK_SCRIPT: &str = r#"#!/bin/sh
 #   PostToolUse   -> Active         (tool finished)
 #   Notification  -> AwaitingInput  (permission / idle notice)
 #   Stop          -> AwaitingInput  (turn ended; waiting on the user)
+#   StopFailure   -> Error          (turn ended on an API error)
 state="$1"
 [ -n "$MAESTRO_SESSION_ID" ] || exit 0
 [ -n "$MAESTRO_URL" ] || exit 0
-# Drain the hook payload so the parent never sees a broken pipe.
-cat >/dev/null 2>&1
+payload=$(cat 2>/dev/null) || true
+body="{\"state\":\"$state\"}"
+# StopFailure payloads carry the outcome in "error". Only a plain enum
+# spelling is reported as the detail — anything else (quotes, backslashes,
+# prose) would risk breaking the JSON body, and the spelling already names
+# the failure.
+detail=$(printf '%s' "$payload" | sed -n 's/.*"error"[[:space:]]*:[[:space:]]*"\([a-z_]*\)".*/\1/p')
+if [ -n "$detail" ]; then
+    body="{\"state\":\"$state\",\"detail\":\"$detail\"}"
+fi
 curl -fsS --connect-timeout 1 --max-time 2 \
     -H 'Content-Type: application/json' \
-    -d "{\"state\":\"$state\"}" \
+    -d "$body" \
     "$MAESTRO_URL/api/sessions/$MAESTRO_SESSION_ID/activity" \
     >/dev/null 2>&1 || true
 exit 0
diff --git a/crates/maestro-hooks/src/tests.rs b/crates/maestro-hooks/src/tests.rs
index 0d79533..6f73169 100644
--- a/crates/maestro-hooks/src/tests.rs
+++ b/crates/maestro-hooks/src/tests.rs
@@ -104,6 +104,40 @@ fn event_state_mapping_matches_the_contract() {
     assert_eq!(map["PostToolUse"], "Active");
     assert_eq!(map["Notification"], "AwaitingInput");
     assert_eq!(map["Stop"], "AwaitingInput");
+    assert_eq!(map["StopFailure"], "Error");
+}
+
+/// A `StopFailure` payload names the API error that ended the turn; the
+/// script reports its `error` spelling as the report's `detail` so a card
+/// can show why (#114).
+#[test]
+fn script_reports_the_error_spelling_as_detail() {
+    let request = capture_request(|url| {
+        sh(
+            HOOK_SCRIPT,
+            &["Error"],
+            &owned_envs(&session_envs(&url)),
+            br#"{"session_id":"abc","hook_event_name":"StopFailure","error":"rate_limit","error_details":"429 Too Many Requests"}"#,
+        )
+    });
+    assert!(request.contains(r#""state":"Error""#), "{request}");
+    assert!(request.contains(r#""detail":"rate_limit""#), "{request}");
+}
+
+/// An `error` value that is not a plain enum spelling (or a payload without
+/// one at all) must never produce a broken body — no detail is posted.
+#[test]
+fn script_posts_no_detail_for_an_unexpected_error_value() {
+    let request = capture_request(|url| {
+        sh(
+            HOOK_SCRIPT,
+            &["Error"],
+            &owned_envs(&session_envs(&url)),
+            br#"{"hook_event_name":"StopFailure","error":"429 \"Too Many\" \\ requests"}"#,
+        )
+    });
+    assert!(request.contains(r#""state":"Error""#), "{request}");
+    assert!(!request.contains("detail"), "{request}");
 }
 
 /// Events whose payload carries no error fields post a bare body — never an
@@ -171,6 +205,7 @@ fn fresh_install_registers_every_event() {
     assert_eq!(cmds.len(), HOOK_EVENTS.len());
     let joined = cmds.join("\n");
     assert_eq!(joined.matches("Active").count(), 2);
+    assert!(joined.contains("Error"));
     assert_eq!(joined.matches("AwaitingInput").count(), 2);
     for cmd in &cmds {
         assert!(cmd.contains(SCRIPT_FILE_NAME));