P6 during the run: split the runner task (02 core, 03 workers); guard.PreCheck as an owner commit; AGENTS.md: write code into files early

Task 02 (the whole runner) ended at 21:08 with no file and no commit: Ornith wrote the
implementation out in its reply (~700 lines), OpenCode compacted the session, and the model
then emitted a malformed tool call. It had also looked for the given test at a wrong path
("_files/…" relative to the plan: my ambiguity).

- 02-runner → 02-runner-core (types, Submit, Status, Touch, Cancel; no goroutines) and
  03-runner-workers; the given test split to match (runner_core_test.go gains three tests:
  queued storage, cancel while queued, Status never moves the lease); later tasks renumbered
  04-09 and every cross-reference checked.
- Copy paths spelled from the repo root.
- guard.PreCheck (+ its test) is committed here by the owner: the old task 05 told the
  implementer to edit internal/guard/, which AGENTS.md forbids. My contradiction.
- AGENTS.md rule 6: write code into files early, in small steps.
Both runner test files compile against a panic-only skeleton (the core file also alone) and
fail there on panic: todo.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plans/p6/_files/config/batch_test.go

@@ -1,6 +1,6 @@
 package config
 
-// P6 task 07: the [batch] block and ParseSize.
+// P6 task 08: the [batch] block and ParseSize.
 
 import (
 	"os"