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>

internal/guard/guard.go

@@ -333,6 +333,21 @@ func ipv4Compatible(addr netip.Addr) (netip.Addr, bool) {
 	return v4, true
 }
 
+// PreCheck is CheckURL without name resolution: scheme, userinfo, host and port, and an IP
+// literal checked against the address rules. A hostname is not resolved here; the fetch-time
+// CheckURL and the dial-time Control still apply to it. The batch endpoint uses it to refuse a
+// target at submit time.
+func (g *Guard) PreCheck(raw string) error {
+	_, literal, err := ParseURL(raw)
+	if err != nil && !(literal.IsValid() && g.allows(literal)) {
+		return err
+	}
+	if literal.IsValid() {
+		return g.CheckAddr(literal)
+	}
+	return nil
+}
+
 // CheckURL parses, and if the host is a name, resolves every record. Any
 // blocked address fails the whole URL (mixed-record trick).
 func (g *Guard) CheckURL(ctx context.Context, raw string) (*url.URL, []netip.Addr, error) {