RegionError "This model is not available in your country" on muse-spark-1.3-contributor from 12 different countries — gateway region gate misfiring

Description

Since 2026-09-08 ~11:00 UTC, all requests to muse-spark-1.3-contributor (and muse-spark-1.2-contributor) via opencode-go fail with:

{"type":"error","error":{"type":"RegionError","message":"This model is not available in your country."}}

The same model worked fine yesterday (2026-09-07) from the same setup. The error is returned before any model invocation — it is a gateway-level region check, not a model error.

This appears to be the same class of bug as #43692 / #39872 / #41518.

What rules out an actual region/IP problem

I systematically tested every hypothesis:

1. Multiple exit countries — all rejected. Switched my proxy through 12 nodes across 7 countries (all widely-supported regions), tested each:

If this were a genuine geo restriction, these 7 countries would not all be rejected.

2. Both muse versions rejected, both endpoints:

• muse-spark-1.3-contributor via POST /zen/go/v1/chat/completions → RegionError
• muse-spark-1.3-contributor via POST /zen/go/v1/responses → RegionError
• muse-spark-1.2-contributor via POST /zen/go/v1/chat/completions → RegionError

3. Account/key is fine — control test passes. Same API key, same IP, same minute:

POST /zen/go/v1/chat/completions  model=kimi-k3  → HTTP 200, normal completion

4. Model is listed as available. GET /zen/go/v1/models returns both muse-spark-1.2-contributor and muse-spark-1.3-contributor.

5. Minor inconsistency observed: some requests to muse intermittently return {"type":"error","message":"Internal server error"} instead of RegionError (possibly related to #40453), suggesting the gateway is currently unstable on this model family.

Repro

curl -s -X POST "https://opencode.ai/zen/go/v1/chat/completions" \
  -H "Authorization: Bearer $OPENCODE_GO_API_KEY" \
  -H "x-opencode-session: t1" \
  -H "Content-Type: application/json" \
  -d '{"model":"muse-spark-1.3-contributor","messages":[{"role":"user","content":"Reply with exactly: OK"}],"max_tokens":10}'

Environment

• Client: opencode (Bun build), model id opencode-go/muse-spark-1.3-contributor
• Subscription: OpenCode Go (active, paid)
• First failure: 2026-09-08 ~11:00 UTC (worked normally on 2026-09-07)
• In TUI the error surfaces as AI_APICallError: This model is not available in your country. on both build and title agents

Expected behavior

Either muse models should work from these regions as they did yesterday, or the model should be removed/region-flagged in /models. The region gate for the muse family appears to be misconfigured.

Start by reproducing the failure with the curl request against /zen/go/v1/chat/completions and compare it with the kimi-k3 control request and GET /zen/go/v1/models. Trace the gateway region check for the muse-spark models and compare it with the behavior described in #43692, #39872, and #41518. Done means supported regions can invoke the listed models, or unavailable models are correctly removed or region-flagged.