fix(mcp): artifact URLs actually resolve — route /artifacts + durable store

[ecto]

What

Every artifact handle on the hosted deploy was a dead end, from two stacked bugs:

1. The /artifacts route was never wired into the deployment. The Build Output API routing table in services/mcp/build.sh has explicit routes for /mcp, /health, /live/*, /oauth/* — but not /artifacts/(.*). The path never reached the function; Vercel's platform answered 403. handleArtifactRequest was dead code in prod. Added the route (GET/HEAD/OPTIONS → the mcp function).

2. The store was a per-instance in-memory Map (documented as such in the file header, with this exact fix named as the follow-up). Even with the route, a handle minted by export_gerber on one serverless instance was unreadable everywhere else: quote_manufacturing rejected a fab_artifact_id minted 2 minutes earlier on the same deployment ("Unknown or expired"), and cold instances 404'd downloads.

The store now mirrors session-store.ts exactly: the in-memory registry becomes a warm-instance cache in front of a durable, service-role-only mcp_artifacts table (migration 033), gated by the same SUPABASE_URL/SUPABASE_SERVICE_ROLE_KEY env and using the same injectable sessionFetch test seam.

• Writes stay sync for callers: storeArtifact caches, kicks off a best-effort persist, and entry.ts awaits flushArtifacts() alongside flushTelemetry() so the write survives the instance freeze.
• Cross-instance reads go async with hydrate-on-miss: the /artifacts route and quote_manufacturing/place_order use getArtifactAsync / resolveArtifactRefAsync. Expired durable rows read as absent and are lazily deleted; cleanup_expired_mcp_artifacts() sweeps never-read rows (same cron follow-up as migration 025's session sweep).
• Observable: server_info and /health now report artifact_store: supabase|in-memory next to session_store.
• Degrades safely: a durable outage falls back to warm-cache-only (today's behavior) — never a tool failure.

Field repro

TMP-1 motor-board session on prod f6d9258: export_gerber returned art_LWz9vu0YPGcqL5HA with a 24 h expiry; the URL 403'd from two independent networks, and quote_manufacturing couldn't bind the freshly re-minted art_FeCf9KhrUVklPMAQ two minutes after creation. The session had to fall back to export_kicad's inline path to deliver fab files at all.

Tests

• 6 new durable-store cases in artifact-store.test.ts: cold-start hydrate (registry cleared between write and read — the shipped failure), route serving from the durable row, cross-instance quote binding, warm-cache rehydration (no double fetch), expiry-as-absent + lazy delete, and degraded-write fallback.
• Full @vcad/mcp suite: 721 passed / 47 files.
• Routing heredoc JSON validated; @vcad/mcp build green.

Deploy notes

• Apply supabase/migrations/033_mcp_artifacts.sql before/with the deploy (table is additive; no existing reads change until it exists — persist failures just log).
• No env changes: durability keys off the same Supabase env sessions already use.

🤖 Generated with Claude Code

https://claude.ai/code/session_018uDJYmC9cSQhB3tPwNUtnD

---

Generated by Claude Code

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
vcad-mcp	Building	Preview, Comment	Jul 8, 2026 10:47pm

3 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
mecheval	Ignored		Jul 8, 2026 10:47pm
vcad	Ignored		Jul 8, 2026 10:47pm
vcad-docs	Ignored		Jul 8, 2026 10:47pm

[chojiai]

What shipped

Artifact links generated by export_gerber and export_cad now work reliably. Two bugs were fixed: the download route was never connected to the hosted deployment, so every artifact URL returned an error regardless of network; and the files themselves were only held in memory on the server instance that created them, so a handle produced in one request was invisible to any other — causing quote_manufacturing to reject a valid fab file as "unknown or expired" minutes after it was exported. Artifacts are now stored durably so any request can retrieve them, and the download route is properly wired.

---

_{Plain-English summary generated by Choji from this pull request.}