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/implementer-lessons.md

@@ -16,16 +16,18 @@ How it is used:
 
 | # | Tip | Evidence | In AGENTS.md | Seen again |
 |---|---|---|---|---|
-| I1 | When a rule says "every" or "everywhere", finish by listing each place it could apply (every struct and enum in the file, every script, every branch) and check them one by one. An example in the task shows one place; the rule covers all of them. | M1 finding 1: `deny_unknown_fields` was put on both enums in task 06, where the task's example showed it, and on neither struct. In task 03, where the task said "works on structs and on enums", every type got it. | yes | M2a: no. All six config structs have it; none of the server-format structs do. |
-| I2 | A check must fail when it cannot do its job: missing input, unreadable file, a tool that errors. Never throw errors away (`2>/dev/null`, `\|\| true`, an ignored `Result`). | M1 finding 4: all three gate scripts passed when `crates/` did not exist, and hid `find` and `awk` errors. | yes | M2a: no recurrence. |
+| I1 | When a rule says "every" or "everywhere", finish by listing each place it could apply (every struct and enum in the file, every script, every branch) and check them one by one. An example in the task shows one place; the rule covers all of them. | M1 finding 1: `deny_unknown_fields` was put on both enums in task 06, where the task's example showed it, and on neither struct. In task 03, where the task said "works on structs and on enums", every type got it. | yes |  M2a: no. All six config structs have it; none of the server-format structs do. M2b: partly. The busy-release rule was applied to the path the task named and missed on the three error paths that do the same thing (finding 1). |
+| I2 | A check must fail when it cannot do its job: missing input, unreadable file, a tool that errors. Never throw errors away (`2>/dev/null`, `\|\| true`, an ignored `Result`). | M1 finding 4: all three gate scripts passed when `crates/` did not exist, and hid `find` and `awk` errors. | yes |  M2a: no recurrence. M2b: partly. An unreadable core.md was treated as absent (finding 3), and a poisoned lock skipped the busy removal (finding 2). |
 | I3 | Report every problem found, not only the first. | M1 finding 8: `check-lines.sh` exits at the first long file. | yes | M2a: not exercised. |
 | I4 | Run the formatter before the gate, and let it decide ordering. | M1 finding 7: three first-gate failures were rustfmt reordering `lib.rs`. | yes | M2a: no fmt failures; the first-gate failures were clippy. |
-| I5 | Log every attempt, including one you abandon. | M1 review: the task 01 row mentions files "from a prior attempt" that has no row of its own. | yes | M2a: partly. Task 11's `stopped` row was overwritten by its later `done` row. |
+| I5 | Log every attempt, including one you abandon. | M1 review: the task 01 row mentions files "from a prior attempt" that has no row of its own. | yes |  M2a: partly. Task 11's `stopped` row was overwritten by its later `done` row. M2b: no recurrence; all ten rows correct, one with a stray pipe. |
 | I6 | Prefer a conversion that can fail (`u32::try_from`) to a cast that is only safe because of a check somewhere else (`as u32`). | M1 finding 6: bounded `as` casts in `frame.rs`. Correct today, but the safety depends on a line ten lines away. | no (already implied by the code rules) | M2a: no `as` casts at all. |
-| I7 | A `read` returns as soon as it has any data to give. It blocks only when it has none. Never keep reading to fill the caller's buffer. | M2a finding 2: the chunked reader delivered a whole stream at its end. | yes | |
+| I7 | A `read` returns as soon as it has any data to give. It blocks only when it has none. Never keep reading to fill the caller's buffer. | M2a finding 2: the chunked reader delivered a whole stream at its end. | yes | M2b: no recurrence. |
 | I8 | When forwarding between two connections, pass a close on in both directions. Do not rely on the client half-closing first. | M2a finding 1. | no (specific to inferproxy) | |
-| I9 | Never end a turn by describing what you are about to do. Do it, then report. | Two Ornith turns in M2a ended with a "## Objective" plan and no tool call. | yes | |
+| I9 | Never end a turn by describing what you are about to do. Do it, then report. | Two Ornith turns in M2a ended with a "## Objective" plan and no tool call. | yes | M2b: not seen; all ten tasks ran unattended to a commit. |
 | I10 | If a tool you were told to use does not exist, stop and say so. Do not invent a command in its place. | Laguna as coordinator ran `opencodec`, which does not exist, and then diagnosed its own typo. | yes | |
+| I11 | A rule about one path applies to every path that does the same thing. If a task says "release X before the final frame", every final frame counts, including the error frames written earlier in the function. | M2b finding 1. | yes | |
+| I12 | A file that exists but cannot be read is an error. Only a file that does not exist may be treated as absent. | M2b finding 3. | yes | |
 
 ## Tips for writing tasks
 
@@ -44,6 +46,8 @@ How it is used:
 | T11 | Make the fake client behave like the real one. If the real client never half-closes, no test client may half-close either. | M2a finding 1: all test clients half-closed; `loopd` does not. |
 | T12 | A weak model should not coordinate other sessions. Use the shell driver (`tools/run-plan.sh`), whose checks are code. | The `opencodec` episode. |
 | T13 | Set the sampling defaults on the server for coding agents (`temp`, `top-p`, `top-k`, `reasoning-budget`). OpenCode sends none, so the server's default temperature of 1.0 applies, and thinking has no cap. | Five Ornith turns ran 16k tokens of thinking to the output limit and produced nothing. |
+| T14 | When a rule has a "before the final frame" or "on every exit" shape, list the exits in the task, or say "including the early returns". The implementer follows the path the task walks through. | M2b finding 1: task 07 walked the success path and the turn's error; the open and create errors were early returns it did not mention. |
+| T15 | Running the whole plan through `tools/run-plan.sh` worked: ten tasks, one commit each, unattended, in about three hours. Keep the TUI closed while it runs; a second message into the driver's session starts a second agent on the same tree. | M2b run, 2026-09-18. |
 
 ## What worked and should be kept
 
@@ -76,3 +80,8 @@ missing; its two failure modes were runaway thinking to the output limit and end
 plan instead of a tool call. GLM-5.3 did one task, the assembler, correctly and quickly, with the
 best comments of the milestone. Laguna did three and a half tasks in M2a with more nudging than in
 M1, and failed as a coordinator. First-gate pass rate for the milestone: 8 of 13.
+
+M2b was Ornith alone, driven by the shell script: ten tasks, ten commits, no intervention, first
+gate 4 of 10, and four low findings in review, two of which are the "everywhere" pattern again in
+a new shape (paths instead of types). Its code reads well and follows the numbered steps in the
+tasks closely; where the task did not walk a path, the rule was not applied there.