feat: editor-v2 assemble lane — multi-clip/card timeline rendering in the worker

Per the adopted qwen38 plan §2 (+ glm53 amendments): video_processing_jobs
kind 'assemble' (claim widened via 044), EdlPlan mirror validation
(lenient-fail), the filter_complex builder (interleaved concat pairs, fit
cover/contain chains, absolute-timeline PNG overlays with enable windows,
VO adelay/sidechain duck, hard-breaking word wrap for card PNGs), and the
runner's assemble path with pre-spawn trim gates, attempt backoff and 15-min
cap. Sources open by magic (SPENC1 kek / SPENC2 direct key) so direct-to-R2
uploads assemble without the api ever seeing bytes. Tests: builder 18,
edl-plan 12, overlay-png 3, runner fakes extended.

apps/api/migrations/044_assemble_claim.sql

@@ -0,0 +1,54 @@
+-- 044: the produce worker claims ASSEMBLE jobs (editor-v2 L1, the worker assemble lane).
+--
+-- An assemble row is an editor-v2 timeline render: input_json carries
+-- { edlProjectId, project: EdlProject } (the EDL shapes live in
+-- apps/api/src/media-control/edl.ts), video_asset_id points at the project's
+-- first source clip, and the produced output is a derived video_assets row
+-- exactly like a compose/mix produce. 043 owns the intake half of the feature
+-- (edl_projects + widening video_processing_jobs.kind's CHECK to admit
+-- 'assemble'); THIS migration is only the worker's half — the claim's kind
+-- filter widened so the lane can pick those rows up.
+--
+-- Same body as 042 with 'assemble' added to the kind list; 'transcoding'
+-- remains the lease state and the stale-lease sweep is unchanged, so a worker
+-- that dies mid-assembly still hands its row back through the same path a
+-- dead compose/mix encode does today.
+
+CREATE OR REPLACE FUNCTION produce_job_claim(p_lane text, p_stale_after interval)
+RETURNS TABLE (
+  id uuid,
+  workspace_id uuid,
+  kind text,
+  input_json jsonb,
+  video_asset_id uuid
+)
+LANGUAGE plpgsql SECURITY DEFINER SET search_path = public AS $$
+BEGIN
+  UPDATE video_processing_jobs stale
+     SET state = 'queued', progress_percent = 0, error = NULL, updated_at = now()
+   WHERE stale.state = 'transcoding'
+     AND stale.updated_at < now() - p_stale_after;
+
+  RETURN QUERY
+  UPDATE video_processing_jobs j
+     SET state = 'transcoding', progress_percent = 5, error = NULL, updated_at = now()
+   WHERE j.id IN (
+     SELECT c.id
+       FROM video_processing_jobs c
+      WHERE c.kind IN ('probe', 'compose', 'mix', 'assemble')
+        AND c.state = 'queued'
+        AND (
+              (p_lane = 'remote' AND c.input_json->>'lane' = 'remote')
+           OR (p_lane <> 'remote' AND c.input_json->>'lane' IS DISTINCT FROM 'remote')
+            )
+      ORDER BY c.created_at, c.id
+        FOR UPDATE SKIP LOCKED
+        LIMIT 1
+   )
+  RETURNING j.id, j.workspace_id, j.kind, j.input_json, j.video_asset_id;
+END
+$$;
+
+-- Ownership unchanged from 040/042.
+REVOKE ALL ON FUNCTION produce_job_claim(text, interval) FROM PUBLIC;
+GRANT EXECUTE ON FUNCTION produce_job_claim(text, interval) TO sp_app;