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/api/batchrun_test.go

@@ -1,7 +1,7 @@
 package api
 
-// P6 task 05: the runner wired to fetchTarget and the metrics, with no HTTP yet. The helpers
-// here (newBatchServer, pageServer, fakeDNS) are shared with task 06's batch_test.go.
+// P6 task 06: the runner wired to fetchTarget and the metrics, with no HTTP yet. The helpers
+// here (newBatchServer, pageServer, fakeDNS) are shared with task 07's batch_test.go.
 
 import (
 	"context"