Dry-run an H3 Max Recast from MCP: dry_run and max_spend_usd

Why preview a Recast

Recast bills by the second of source video. fal's page, read 2026-10-03, lists $0.30 per second at 768p and $0.45 per second at 1080p, with reference photos included. Sume bills the list with its 1.25 margin. A 30-second clip at 1080p is a noticeably bigger charge than a 6-second clip at 768p, so the first call to an agent-driven swap should be a preview.

The gates on Sume's hosted MCP

The MCP tools and gates page lists the gates on paid tools such as generate_video. They are the same whether the caller is an editor, an agent or a script.

The order of calls

Call tools_schema with name: "generate_video" to read the contract. Then call generate_video with dry_run: true, the model h3-max-recast, the source video_url, the photos and the source length as duration, and read the estimate against your balance. Repeat the same call without dry_run, with a fresh idempotency_key and a max_spend_usd just above the estimate.

Then use jobs_wait and jobs_result to collect the output. The docs say to poll with jobs_status or jobs_wait, then read jobs_result, and to prefer media.sume.com URLs in reports over signed URLs.

Things to remember

• A dry run needs the same inputs as the real call, so a wrong duration shows up in the preview.
• max_spend_usd applies only when you pass it. An agent that omits it has no per-call cap from this field.
• Reuse the same idempotency_key to retry a transport failure, and use a new one for a deliberate second take.
• Recast has no seed on Sume, so a second take is a second charge.