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/p6/01-batchstore.md

@@ -5,7 +5,7 @@
 
 Add the batch job store to the existing `internal/dcache` SQLite database. No HTTP, no worker —
 this task is storage only. `dcache` owns the single SQLite connection, so the batch tables and
-their accessors live here; the runner (task 02) and API (task 05) call them.
+their accessors live here; the runner (task 02) and the API (tasks 06–07) call them.
 
 ## Context
 
@@ -102,9 +102,9 @@ caller decides the clock, so the given test asserts exact lease values.
    `UpdateBatchTarget`, `SetBatchJobStatus`, `TouchBatchJob`, and `MarkInFlightFailed` set the job
    lease to their `now`. **Reads never write:** `BatchJob`, `BatchTargets` and the counts change
    nothing, so the given test can assert exact lease values after reading. A consumer's read keeps
-   a job alive because the API calls `TouchBatchJob` after it (task 05), not because the read does.
+   a job alive because the API calls `TouchBatchJob` after it (task 07), not because the read does.
 2. **No partial-job reads leak a competing caller.** Every accessor is keyed by `job_id` only; the
-   caller filter is the API layer's job (task 05). The store stores what it is told and returns
+   caller filter is the API layer's job (task 07). The store stores what it is told and returns
    what is asked.
 3. **Idempotency lookup.** `BatchJobByIDem(caller, idemKey, now, ttl)` returns the id of a job with
    that `(caller, idem_key)` whose `lease + ttl > now` **and whose status is `queued`, `running`,
@@ -123,7 +123,7 @@ caller decides the clock, so the given test asserts exact lease values.
    after each target result is written; it is separate from the content-cache `evict()`.
 7. `MarkInFlightFailed(reason, now)` marks every `queued`/`running` job `failed` with
    `error=reason`, bumps their lease to `now`, and returns the count. This is the restart
-   reconciliation hook; `serve` calls it on startup (task 06).
+   reconciliation hook; `serve` calls it on startup (task 08).
 8. `BatchNbytes()` sums `nbytes` over `batch_job`. Batch bytes are **not** included in `Size()` or
    the content `evict()` union; batch is a coherent unit with its own budget.
 9. Accessors follow the existing `dcache` style: return `(value, bool)` or `error`, never panic,
@@ -132,7 +132,7 @@ caller decides the clock, so the given test asserts exact lease values.
 
 ## Given
 
-Copy `_files/dcache/batch_test.go` → `internal/dcache/batch_test.go`. It opens an in-memory `DB`
+Copy `docs/plans/p6/_files/dcache/batch_test.go` → `internal/dcache/batch_test.go`. It opens an in-memory `DB`
 and asserts the create/read round trip, `BatchJobByIDem` lease expiry, caller scoping and the
 status filter (rule 3), live-job
 counts, ordered targets, the exactly-once `targets_done`/lease-bump rules, `SweepBatch`,