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/11-review-fixes.md

@@ -0,0 +1,74 @@
+# M2b task 11: four small fixes (review follow-up)
+
+**Branch:** `m2b` (run `git switch m2b`; `git status --short` must be empty, otherwise stop)
+**Commit subject:** `Fix four review findings: busy release, poison recovery, core.md errors, chat loop`
+
+## Goal
+
+The M2b review found four small defects. Two have a test to copy in; two are rules to apply. None
+changes an interface.
+
+## Files
+
+- Copy (replacing the old ones): `crates/loopd/tests/baseline.rs`, `crates/bxctl/tests/chat.rs`
+- Modify: `crates/loopd/src/channel.rs`, `crates/loopd/src/baseline.rs`,
+  `crates/bxctl/src/chat.rs`, `crates/bxctl/src/main.rs`, `docs/implementer-log.md`
+
+## The four fixes
+
+1. **`channel.rs`: release the session before *every* final frame.** Task 07 said to drop the
+   busy guard before `turn_done` or the turn's error, and that is done. But the error frames for
+   a session that cannot be opened or created (`no_such_session`, `session_exists`, `internal`)
+   are still sent while the session is marked busy. `bxctl chat --session <new id>` reads
+   `no_such_session` and at once sends the same turn again with `resume: false`, so it can be
+   answered `session_busy` by a server thread that has not returned yet. Drop the guard before
+   each of those three writes. The rule: the last frame of a connection is never sent while the
+   session is busy.
+2. **`channel.rs`: a poisoned lock must not leave a session busy forever.** The guard's `Drop`
+   does `if let Ok(mut busy) = self.ctx.busy.lock()`, which skips the removal when the lock is
+   poisoned. Recover it with `unwrap_or_else(|p| p.into_inner())`, as `handle` already does.
+3. **`baseline.rs`: a `memory/core.md` that exists but cannot be read is an error.** Today
+   `if let Ok(text) = read_to_string(..)` treats an unreadable file like a missing one, so a
+   session starts without the memory the owner curated, and nothing says so. If the file exists,
+   a read failure is `BaselineError::Read(path, e)`. A missing file is still fine.
+4. **`bxctl`: the interactive loop goes on after a failed turn, and `new_session_id` has no
+   `expect`.** The spec says "A failed turn prints `bxctl: <error>` and the loop goes on"; today it
+   exits 1. Report the error and continue; the session exists, so the next line resumes it. And
+   `AGENTS.md` forbids `expect` in library code: replace the two in `new_session_id` with
+   `unwrap_or_default()` for the clock and `unwrap_or_else` with a fixed valid id for the
+   `SessionId` (it cannot fail, but the type must not be forced).
+
+## Steps
+
+- [ ] **1. Copy.**
+
+```sh
+git switch m2b
+cp docs/plans/M2b/files/crates/loopd/tests/baseline.rs crates/loopd/tests/
+cp docs/plans/M2b/files/crates/bxctl/tests/chat.rs crates/bxctl/tests/
+```
+
+- [ ] **2. See them fail.** `cargo test -p loopd --test baseline`: 1 of 7 fails,
+  `an_unreadable_core_memory_file_is_an_error`. `cargo test -p bxctl --test chat`: 1 of 12 fails,
+  `interactive_mode_survives_a_failed_turn`.
+- [ ] **3. Make the four fixes.** Run `cargo fmt --all`.
+- [ ] **4. See them pass.** `cargo test -p loopd --test baseline --test channel -p bxctl`.
+  Expected: 7, 6 and 12 passed. Run the `channel` tests ten times in a row.
+- [ ] **5. Run the gate.** `make gate`. Expected last line: `gate: ok`.
+- [ ] **6. Log and commit.**
+
+```sh
+git add crates/loopd crates/bxctl docs/implementer-log.md
+git commit
+```
+
+## Done when
+
+- `make gate` prints `gate: ok` with 219 tests.
+- `grep -n "expect(" crates/bxctl/src/chat.rs` prints nothing.
+- `grep -c "drop(held)" crates/loopd/src/channel.rs` prints 4 (or the guard is scoped so that
+  every final frame is written after it is gone).
+
+## Stop and report if
+
+- `interactive_mode_survives_a_failed_turn` cannot pass without changing what `--say` does.