Review M2b: accept with one follow-up task; record lessons

All ten tasks pass the checklist, the gate, the audit and the device
checks, including a four-turn conversation with a loopd restart and no
cache loss. Reading and probing found four low defects: the busy guard
is released before the final frame on the main path but not on the
three error paths, its Drop skips a poisoned lock, an unreadable
core.md is treated as missing, and bxctl's interactive loop exits on a
failed turn. Task 11 carries the fixes with two new tests, checked
against a fixed copy of the branch.

The Model column is filled in (all Ornith) and one malformed row is
repaired. Two rules are promoted to AGENTS.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/plans/M2b/files/crates/bxctl/tests/chat.rs

@@ -57,6 +57,8 @@ fn fake_loopd(events: Vec<TurnEvent>, end: End) -> FakeLoopd {
             let id = request.id;
             let end = if turn.resume && turn.content == "trigger-no-such-session" {
                 End::Error(ErrorCode::NoSuchSession, "session x does not exist")
+            } else if turn.content == "trigger-turn-limit" {
+                End::Error(ErrorCode::TurnLimit, "the turn hit a limit")
             } else {
                 end.clone()
             };
@@ -417,3 +419,45 @@ fn bad_arguments_print_usage() {
         .unwrap();
     assert_eq!(output.status.code(), Some(2));
 }
+
+/// A failed turn is reported, and the conversation goes on: the session still exists and the
+/// next line is a new turn on it.
+#[test]
+fn interactive_mode_survives_a_failed_turn() {
+    let fake = fake_loopd(
+        vec![TurnEvent::Content {
+            text: "ok".to_string(),
+        }],
+        End::Done(TurnDone {
+            content: "ok".to_string(),
+            usage: usage(),
+        }),
+    );
+    let mut child = Command::new(env!("CARGO_BIN_EXE_bxctl"))
+        .args(["chat", "--socket"])
+        .arg(&fake.socket)
+        .stdin(std::process::Stdio::piped())
+        .stdout(std::process::Stdio::piped())
+        .stderr(std::process::Stdio::piped())
+        .spawn()
+        .unwrap();
+    {
+        let mut stdin = child.stdin.take().unwrap();
+        std::io::Write::write_all(&mut stdin, b"first\ntrigger-turn-limit\nthird\n/quit\n")
+            .unwrap();
+    }
+    let output = child.wait_with_output().unwrap();
+    assert!(
+        output.status.success(),
+        "a failed turn does not end the chat"
+    );
+    let stderr = String::from_utf8_lossy(&output.stderr);
+    assert!(
+        stderr.contains("turn limit: the turn hit a limit"),
+        "{stderr}"
+    );
+    let turns = fake.turns.lock().unwrap();
+    assert_eq!(turns.len(), 3, "the turn after the failure was sent");
+    assert!(turns[2].resume, "and it resumed the same session");
+    assert_eq!(turns[2].session, turns[0].session);
+}