fix(render): node reports progress → moving bar + ETA (was stuck 0%/Preparing)

The node's onProgress callback only LOGGED — it never POSTed, so render_progress stayed
0 and step stayed Preparing (no bar, no ETA). Add render-svc POST
/v1/internal/render/jobs/{id}/progress (UpdateJobProgress: set render_progress + bump
step Queued/Preparing→Rendering once >0) + client UpdateProgress + wire onProgress to
post it (8s best-effort timeout, AE-CPU/DB-starvation tolerant). Preview already posts;
real-frame preview is epic C.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/render/internal/db/db.go

@@ -750,6 +750,29 @@ func (s *Store) UpdateJobPreview(ctx context.Context, jobID uuid.UUID, imageB64
 	return err
 }
 
+// UpdateJobProgress stores the render percentage for a running job and advances the
+// step to 'Rendering' once it actually starts (so the UI shows progress + ETA, not a
+// stuck 'Preparing'). Called by the node agent every few seconds during a render.
+func (s *Store) UpdateJobProgress(ctx context.Context, jobID uuid.UUID, progress int) error {
+	if progress < 0 {
+		progress = 0
+	}
+	if progress > 100 {
+		progress = 100
+	}
+	_, err := s.pool.Exec(ctx, `
+		UPDATE render.render_jobs
+		SET render_progress = $1,
+		    step = CASE WHEN step IN ('Queued'::render_step, 'Preparing'::render_step) AND $1 > 0
+		                THEN 'Rendering'::render_step ELSE step END,
+		    started_at = COALESCE(started_at, NOW()),
+		    updated_at = NOW()
+		WHERE id = $2
+		  AND step NOT IN ('Done'::render_step, 'Failed'::render_step, 'Cancelled'::render_step)`,
+		progress, jobID)
+	return err
+}
+
 func (s *Store) CancelJob(ctx context.Context, id, userID uuid.UUID) (bool, error) {
 	tag, err := s.pool.Exec(ctx, `
 		UPDATE render.render_jobs

services/render/internal/handlers/internal.go

@@ -235,6 +235,28 @@ func (h *InternalHandler) Preview(c *gin.Context) {
 	c.Status(http.StatusNoContent)
 }
 
+// POST /v1/internal/render/jobs/:job_id/progress
+// Node agent pushes the render percentage so the UI shows a moving bar + ETA.
+func (h *InternalHandler) RenderProgress(c *gin.Context) {
+	jobID, err := uuid.Parse(c.Param("job_id"))
+	if err != nil {
+		c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: "invalid job_id"})
+		return
+	}
+	var req struct {
+		Progress int `json:"progress"`
+	}
+	if err := c.ShouldBindJSON(&req); err != nil {
+		c.JSON(http.StatusBadRequest, models.APIError{Code: "bad_request", Message: err.Error()})
+		return
+	}
+	if err := h.store.UpdateJobProgress(c.Request.Context(), jobID, req.Progress); err != nil {
+		c.JSON(http.StatusInternalServerError, models.APIError{Code: "internal_error", Message: err.Error()})
+		return
+	}
+	c.Status(http.StatusNoContent)
+}
+
 // POST /v1/internal/render/jobs/claim
 // Node agent calls this to atomically claim the next queued job.
 // Returns 204 when there is nothing queued (agent should back off and retry).