M4b review of tasks 16 to 18; tip T32

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/implementer-log.md

@@ -648,3 +648,22 @@ right.
 
 **The run.** Task 15's first session stopped on finding 4. After the listed fix, task 15 finished
 on its first session.
+
+### M4b, tasks 16 to 18 — reviewed 2026-09-24 by the design model (Claude)
+
+Accepted. Findings 1 and 2 of the review above are closed in code; finding 1 still needs the check
+on the owner's server, with the second account sending a direct message. The three commits carry
+the trailer. The given tests are identical to the plan. The code in `crates/` is byte-identical to
+the reference. `make gate` gives `gate: ok` with 854 tests, the count the plan gave.
+
+Tasks 16 and 17 passed the gate on their first run. Task 18 needed six runs, and none of the
+failures was in its own code. Once, `serve_restart`'s
+`a_restart_reports_the_cut_off_turn_and_catches_up` (a given test from M4a) failed with the two
+caught-up turns in the wrong order. The session handled it well: it did not edit the given test,
+and it did not change code outside the task. It showed the failure also happens without its
+change (40 of 40 and 30 of 30 runs under load), and reported it in the log row.
+
+The fault was the design model's, in M4a. Those two posts are two sessions, whose turns run on
+their own threads, so the order they reach `loopd` is up to the scheduler: under load, 1 run in 60
+failed. `mm_json.rs` already checks the order of catch-up, so the test now compares the two turns
+as a set (a43d997; 100 of 100 runs under load; tip T32).