Web turn validation falls back to DEFAULT_WEBUI_MODEL_IDS and refuses custom models the picker offers (surfaces as bare HTTP 403)

[trackport-dev]

Version: CLI 0.1.7 (core image from the 0.1.7 manifest). Harness: pi.

What happened

With a custom provider registered (PUT /v1/admin/custom-providers/...), the web-UI picker lists the custom model (surface.ts builds webuiModels from the live catalog, which includes custom models). Selecting it and sending a message fails with a bare HTTP 403 in the web UI.

Why

validateWebTurnModelOptions() (src/core/turn-options.ts:47-58) is called from app.turn() with enabledWebuiModels. When the org has no web-UI allowlist configured and no OpenRouter key, enabledWebuiModels is null, so the function falls back to DEFAULT_WEBUI_MODEL_IDS — the hardcoded registry list — which never contains custom models. The turn is refused with "that model is not enabled for the web UI"; postTurn maps refused to 403 (src/api/routes/turns.ts); and the web-UI client shows o?.message ?? o?.error ?? \HTTP ${status}`, but the refusal body carries reason, not message/error, so the operator only sees HTTP 403` with no explanation.

So the picker and the validator disagree: the picker offers the model, the validator refuses it. Workaround: configure an explicit allowlist in Governance → Allowed models that includes the custom model.

Suggested fix

• In validateWebTurnModelOptions, treat the fallback set as DEFAULT_WEBUI_MODEL_IDS ∪ customModelCatalog().map(m => m.id) (same source the picker uses), or pass the picker's computed allowed list through.
• Surface reason from a refused turn in the web UI instead of the bare status.

Repro

1. Fresh org, no "Allowed models" configured, no OpenRouter key.
2. Register any custom provider with one model via Admin → Onboarding → Custom providers.
3. Web chat → pick the custom model → send a message. Expected: turn runs. Actual: HTTP 403; nothing in error_events.