docs: M5d-2: read only the implementer-log header

Task 06 opened the whole implementer log (~360 kB) after reading supporting
modules; OpenCode returned "Context size has been exceeded" and made no
commit. AGENTS.md and tasks 06-10 now say to read the first 12 lines only.

Co-Authored-By: Grok 4.6 <noreply@x.ai>

docs/plans/M5d2/07-loopd-scheduler-cron.md

@@ -28,6 +28,9 @@ is not busy). Speaker `None`. Same time-line prefix as heartbeat.
 - Modify: `crates/loopd/src/scheduler.rs`, `docs/implementer-log.md`.
 - Do not touch: any other file.
 
+**Read only what the step names.** Step 1 is the `cp`. At the log step, read only the first 12
+lines of `docs/implementer-log.md`. Do not load the rest of that file.
+
 ## Facts you need
 
 - **Load.** `jobs::load(&ctx.cfg.paths.home.join("jobs"))`. On `Err`, log `loopd: {e}` and
@@ -84,7 +87,8 @@ Do not change heartbeat behaviour. Do not add a sleep.
 - [ ] **6. Run the gate.** `cargo fmt --all`, then `make gate`, timeout 600000 ms. Last line
   `gate: ok`. Test count **1557** (1551 before, plus 6). After `gate: ok`, do not add up
   `test result:` lines.
-- [ ] **7. Log and commit.** Task cell `M5d2/07-loopd-scheduler-cron`. Stage with
+- [ ] **7. Log and commit.** Task cell `M5d2/07-loopd-scheduler-cron`. Read only the first 12
+  lines of `docs/implementer-log.md`; insert the row under the header. Stage with
   `git add crates/loopd docs/implementer-log.md Cargo.lock`, then commit as `AGENTS.md` says.
 
 ## Done when