Review M2a: accept with two follow-up tasks; record models and lessons

The branch passes every check, including make verify-device on
straylight and repeated timing runs under load. Reading and probing
found that inferproxy does not pass an upstream close on to a client
that is still sending, and that the chunked body reader delivers a
stream only when the caller's buffer fills or the stream ends. Both
were also gaps in the tasks and tests, so tasks 14 and 15 carry the
fixes with new tests checked against the reference.

The Model column is corrected: tasks 04 to 06 and 08 to 13 were Ornith.
Lessons gain four implementer tips and five task-writing tips; three
rules are promoted to AGENTS.md.

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

AGENTS.md

@@ -14,6 +14,8 @@ Unix sockets. You are implementing it one task at a time.
    Do not improvise, do not change a test, do not weaken a check. Add your row to
    `docs/implementer-log.md` with status `stopped`, say what you tried and what happened, commit
    only that file, and tell the owner.
+   A later session that finishes the task adds a new `done` row; it never edits the `stopped`
+   row, because the record of the stop is part of the log.
 
 ## Files you must never edit
 
@@ -55,6 +57,10 @@ These come from defects found in review. The evidence is in `docs/implementer-le
   Never throw errors away with `2>/dev/null`, `|| true` or an ignored `Result`.
 - Report every problem you find, not only the first.
 - Log every attempt, including one you abandon.
+- Never end a turn by describing what you are about to do. Do it, then report.
+- If a tool you were told to use does not exist, stop and say so. Do not invent a command in its
+  place.
+- A `read` returns as soon as it has any data to give and blocks only when it has none.
 
 ## The gate