feat: complete remaining Go backend modules

supabase/schema.sql

@@ -29,6 +29,7 @@ create table if not exists generation_jobs (
   input_urls text[] not null default '{}',
   output_asset_ids text[] not null default '{}',
   provider_task_id text,
+  provider_dispatch_started_at timestamptz,
   request_payload jsonb not null default '{}'::jsonb,
   response_payload jsonb,
   error jsonb,
@@ -43,6 +44,8 @@ create table if not exists generation_jobs (
   locked_by text,
   started_at timestamptz,
   completed_at timestamptz,
+  dispatch_ready_at timestamptz,
+  finalized_at timestamptz,
   webhook_url text,
   webhook_attempts integer not null default 0,
   webhook_last_status jsonb,
@@ -66,6 +69,18 @@ alter table generation_jobs add column if not exists webhook_url text;
 alter table generation_jobs add column if not exists webhook_attempts integer not null default 0;
 alter table generation_jobs add column if not exists webhook_last_status jsonb;
 alter table generation_jobs add column if not exists usage_context jsonb;
+alter table generation_jobs add column if not exists provider_dispatch_started_at timestamptz;
+alter table generation_jobs add column if not exists dispatch_ready_at timestamptz;
+alter table generation_jobs add column if not exists finalized_at timestamptz;
+
+update generation_jobs
+set dispatch_ready_at = coalesce(dispatch_ready_at, created_at, now())
+where dispatch_ready_at is null;
+
+update generation_jobs
+set finalized_at = coalesce(finalized_at, completed_at, updated_at, now())
+where finalized_at is null
+  and status in ('succeeded', 'failed', 'expired', 'cancelled');
 
 create table if not exists usage_events (
   id text primary key,
@@ -147,6 +162,7 @@ create index if not exists assets_owner_created_idx on assets(owner_id, created_
 create index if not exists generation_jobs_owner_created_idx on generation_jobs(owner_id, created_at desc);
 create index if not exists generation_jobs_status_idx on generation_jobs(status);
 create index if not exists generation_jobs_claim_idx on generation_jobs(status, scheduled_at, locked_at, priority desc);
+create index if not exists generation_jobs_finalize_claim_idx on generation_jobs(finalized_at, scheduled_at, locked_at, priority desc);
 create index if not exists generation_jobs_external_client_idx on generation_jobs(owner_id, external_client_id, created_at desc);
 create unique index if not exists generation_jobs_idempotency_idx
   on generation_jobs(owner_id, external_client_id, idempotency_key)
@@ -187,7 +203,9 @@ begin
   with candidates as (
     select id
     from generation_jobs
-    where status in ('queued', 'running')
+    where dispatch_ready_at is not null
+      and finalized_at is null
+      and status in ('queued', 'running', 'succeeded', 'failed', 'expired', 'cancelled')
       and coalesce(scheduled_at, created_at) <= v_now
       and (
         locked_at is null