M4b task 15: fix task 14's dropped refusal reason, as a listed edit

Task 15's session found the defect in serve/approvals.rs, a file it did not list, and stopped.
The comment in task 14 used one name for two values; task 14's tests could not reach it. Lesson T30.

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

docs/implementer-lessons.md

@@ -67,6 +67,8 @@ How it is used:
 
 | T29 | Check a skeleton's comments, not only its code. Print every `todo!()` beside its signature and read each pair before hand-over. Filling the bodies from your own code proves the split can pass; it cannot show that a comment sits on the wrong function. Edit comments by function, never by "the next comment after this name". And tell the implementer to stop and quote a comment that does not fit. | M4a task 14, second session: `post`'s comment was `now_ms`'s text, put there by a script; Ornith saw the contradiction and deliberated over it until the turn ran out. M4a task 16: a comment naming the function it replaced made the task's own `grep` fail; and a given test copied into the plan before `cargo fmt` came back reformatted. Run the task's checks, and `cargo fmt`, on the end state before hand-over. |
 
+| T30 | Every behaviour a task writes must be reachable by that task's own tests. When a function's effect shows only after a later task (here: a refusal's reason, which only task 15 could send), give a unit test in the first task, or write that function in the later one. And never let one name mean two things in a comment: say which `reason`. | M4b task 14 dropped a refusal's reason, reading `Refused -> Ended::Refused { by, reason }` as the `DenyReason` in scope; its tests passed, and task 15's caught it, in a file task 15 could not touch. |
+
 ## What worked and should be kept
 
 - Byte-exact fixtures, compared in both directions. No wire-format defect reached review.