fix(scout): stop retiring realtime models on a wrong-endpoint 404 - #15

Regression from #14, caught by the maintainer within hours of deploy. The auto-retirement disabled gemini-2.5-flash-native-audio-preview-12-2025 and gemini-3.1-flash-live-preview — both working perfectly.

What went wrong

The scout probes Google with generateContent. Realtime models answer only over bidiGenerateContent, so Google replies:

models/gemini-3.1-flash-live-preview is not found for API version v1beta, **or is not supported for generateContent**. Call ModelService.ListModels to see the list of available models and their supported methods.

That 404 describes the endpoint, not the model. isGoneMessage matched on 404/not found, and three cycles later both rows were switched off at gone_streak=3.

The misclassification predates #14 — model_availability.status was already recording these as deprecated. Nothing acted on it until retirement shipped, which is exactly what turned a cosmetic wrong label into disabled models. Retirement didn't create the bug; it made an existing one consequential.

Fixed at both layers

1. isGoneMessage rejects wrong-method 404s — is not supported for, supported methods, not supported by. A wrong-endpoint 404 is never removal, whatever the provider, so this generalises past Google.

2. selectSweepCandidateIds stops feeding non-chat models to a chat probe. A model is swept when it advertises chat or vision, or advertises no capability at all (which the router already treats as unrestricted). Realtime, speech and embedding-only rows are excluded — the probe shouldn't render a verdict it isn't equipped to make.

Layer 2 is the real fix; layer 1 is the net that catches the same shape from any other provider.

Migration V23

Re-enables what the bug retired, scoped to rows whose only capabilities are realtime/audio — so it restores exactly the class the probe cannot judge and never resurrects a genuinely dead chat model. It also clears gone_streak, so a stale counter can't re-retire them before the new candidate query takes effect.

Verification

• 340/340 server tests pass, tsc clean
• The exact production error strings are now negative cases
• A genuine Google removal (no longer available to new users) still retires — the guard is narrow, not a blanket 404 exemption
• New tests assert realtime-only models stay enabled, are excluded from the sweep, and that ordinary chat models are still swept

Note on the deployed state

The two models are currently disabled on the VPS. V23 restores them on the next restart.

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