mAi: #9 - imagen.series (batch tries 1-10 + selection)

Schema (applied via migration imagen_series_init):
- imagen.series parent table (prompt + params + count CHECK 1..10 + selected_image_id)
- imagen.jobs += series_id (FK) + series_idx
- imagen.images += series_id (FK)
- Owner-scoped RLS on series (SELECT/INSERT/UPDATE) + grants
- Partial indexes WHERE series_id IS NOT NULL on both child tables

Worker pipeline:
- worker.Job += SeriesID, populated from imagen.jobs.series_id via the
  claim query.
- cloud.SyncRequest += SeriesID; insertRow writes series_id when non-empty,
  omits the key when empty so solo runs leave the column NULL.
- maybeCloudSync threads seriesID from job.SeriesID through to the cloud
  sink. generate.go (CLI) always passes "" — solo path unchanged.

Tests:
- worker: SeriesID propagates from Job to fakePipeline.lastJob unchanged,
  solo job keeps it empty.
- cloud: SyncRequest.SeriesID lands as row.series_id in the POST body;
  empty SeriesID omits the key entirely.

Refs ImaGen#9.

cmd/imagen/generate.go

@@ -132,7 +132,7 @@ func runGenerate(ctx context.Context, args []string) error {
 		fmt.Fprintln(os.Stderr, "sidecar:", paths.SidecarPath)
 	}
 
-	if result, err := maybeCloudSync(ctx, cfg, noCloud, "", paths, in, res, w, h); err != nil {
+	if result, err := maybeCloudSync(ctx, cfg, noCloud, "", "", paths, in, res, w, h); err != nil {
 		// cloud-sync failures are warnings — the image already wrote.
 		fmt.Fprintln(os.Stderr, "imagen: cloud sync:", err)
 	} else if result != nil && result.ImageID != "" {
@@ -173,7 +173,10 @@ func resolveCloudSyncMode(cfg *config.Config, noCloudFlag bool, env string) (str
 // that need the imagen.images.id (e.g. the worker linking a job row) can pick
 // it up. ownerOverride, when non-empty, wins over config + env — the worker
 // passes the job row's owner_user_id so each job is attributed correctly.
-func maybeCloudSync(ctx context.Context, cfg *config.Config, noCloud bool, ownerOverride string, paths *output.Outputs, in output.Inputs, res *backend.Result, width, height int) (*cloud.SyncResult, error) {
+// seriesID, when non-empty, lands on imagen.images.series_id so the
+// list-page query (`WHERE series_id IS NULL`) hides series members from
+// the flat grid; empty means solo run.
+func maybeCloudSync(ctx context.Context, cfg *config.Config, noCloud bool, ownerOverride, seriesID string, paths *output.Outputs, in output.Inputs, res *backend.Result, width, height int) (*cloud.SyncResult, error) {
 	mode, err := resolveCloudSyncMode(cfg, noCloud, os.Getenv("IMAGEN_CLOUD_SYNC"))
 	if err != nil {
 		return nil, err
@@ -262,6 +265,7 @@ func maybeCloudSync(ctx context.Context, cfg *config.Config, noCloud bool, owner
 		LatencyMs:       latency,
 		CostUSDEstimate: cost,
 		Sidecar:         sidecar,
+		SeriesID:        seriesID,
 	}
 	syncCtx, cancel := context.WithTimeout(ctx, 60*time.Second)
 	defer cancel()

cmd/imagen/worker.go

@@ -112,6 +112,9 @@ func (q *pgxQueue) Close() {
 // returns it. FOR UPDATE SKIP LOCKED is belt + braces against a second worker
 // process — out of scope for v1 but cheap insurance.
 func (q *pgxQueue) ClaimNextPending(ctx context.Context) (*worker.Job, error) {
+	// series_id is nullable on imagen.jobs (solo run when NULL); cast to text
+	// with COALESCE so pgx scans into a plain Go string. Empty string =
+	// solo run; the pipeline skips series propagation in that case.
 	const stmt = `
 		UPDATE imagen.jobs
 		SET status='running', started_at=now()
@@ -126,11 +129,13 @@ func (q *pgxQueue) ClaimNextPending(ctx context.Context) (*worker.Job, error) {
 		          COALESCE(model,''),
 		          COALESCE(width, 0), COALESCE(height, 0),
 		          COALESCE(steps, 0), COALESCE(seed, 0),
-		          COALESCE(style,'')`
+		          COALESCE(style,''),
+		          COALESCE(series_id::text, '')`
 	var j worker.Job
 	err := q.conn.QueryRow(ctx, stmt).Scan(
 		&j.ID, &j.OwnerUserID, &j.Prompt, &j.Backend,
 		&j.Model, &j.Width, &j.Height, &j.Steps, &j.Seed, &j.Style,
+		&j.SeriesID,
 	)
 	if errors.Is(err, pgx.ErrNoRows) {
 		return nil, nil
@@ -258,7 +263,7 @@ func (p *workerPipeline) Run(ctx context.Context, job worker.Job) worker.Outcome
 		// config, the worker can't serve flexsiebels at all.
 		return worker.Outcome{Err: fmt.Errorf("output.cloud_sync=off in config; the worker requires cloud_sync=on or auto")}
 	}
-	syncRes, syncErr := maybeCloudSync(ctx, p.cfg, false, job.OwnerUserID, paths, in, res, dimOrFallback(job.Width, res, "width"), dimOrFallback(job.Height, res, "height"))
+	syncRes, syncErr := maybeCloudSync(ctx, p.cfg, false, job.OwnerUserID, job.SeriesID, paths, in, res, dimOrFallback(job.Width, res, "width"), dimOrFallback(job.Height, res, "height"))
 	if syncErr != nil {
 		return worker.Outcome{Err: fmt.Errorf("cloud sync: %w", syncErr)}
 	}