P6 review: runner shutdown, cancel-while-busy, concurrent submits, batch-off 503, transactional store, CLI 202

Owner review of p6 (Ornith tasks 01-09), with an independent reviewer pass whose findings I
confirmed against the code. Every fix has a regression test that fails on the old code.

internal/batch
- Close let the workers keep draining every live job under the cancelled context, failing
  every target; they now stop at once, store nothing on a failure during shutdown, and leave
  the job live for MarkInFlightFailed("restart").
- A job cancelled while its in-flight target came back busy stayed in the rotation forever
  (depth gauge stuck, job held in memory); it now leaves. The task 03 design had this gap: mine.
- Submit's idempotency lookup, caps and create ran unlocked: 20 concurrent submits by one
  caller made 8 jobs. Serialised with submitMu.
- A failed target insert left a queued job no worker would run (holding the caller's cap);
  it is marked failed.
- A second concurrent cancel returned true and counted twice.
- Config: zero OR negative values take the defaults (negative Workers panicked the
  WaitGroup; a negative TTL or byte budget would sweep or evict everything).
- Retry timing used the pre-fetch time (a 5 s busy answer made RetryWait moot).
- The rotation cursor is kept within [0, len(live)] (it was absolute and drifted on removal).
- The unused in-memory callers map is gone (Submit racing Close wrote to a nil map).
internal/dcache
- PutBatchTargets, SweepBatch and eviction are transactional; the sweep never removes a
  queued or running job.
internal/api
- Every /v1/batch endpoint answers 503 when batch is off; POST panicked on the nil runner.
- GET /{id}/{idx} bounds idx by the rows actually returned.
- batchFetch copies a *fetch.Error instead of mutating one the PDF pool may share.
internal/config
- ParseSize no longer overflows to a negative size.
cmd/sift
- sift batch treated 202 Accepted (submit) as an error and exited 1 with no message.

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

internal/dcache/batch_review_test.go

@@ -0,0 +1,25 @@
+package dcache
+
+// P6 owner review: the sweep never removes a live job.
+
+import (
+	"testing"
+	"time"
+)
+
+func TestSweepSparesLiveJobs(t *testing.T) {
+	db := newBatchDB(t)
+	for _, st := range []string{"queued", "running", "done"} {
+		if err := db.CreateBatchJob(BatchJob{ID: st, Caller: "a", CallerClass: ClassFleet, IDemKey: st, Status: st, TargetsTotal: 1, CreatedAt: 1, Lease: 1}); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if n := db.SweepBatch(1_000_000, time.Hour); n != 1 {
+		t.Fatalf("swept %d, want only the done job", n)
+	}
+	for _, id := range []string{"queued", "running"} {
+		if _, ok := db.BatchJob(id); !ok {
+			t.Fatalf("live job %s was swept", id)
+		}
+	}
+}