fix(gemini): repoint providers off models retired for new API keys

[posthog]

Fixes the Gemini provider being completely broken for users with freshly created Google API keys.

Why

New keys default to gemini-2.5-flash-lite, which Google now 404s with NOT_FOUND ("no longer available to new users"), so memory generation silently fails for the affected cohort. The providers also hard-coded several other retired IDs (gemini-2.5-flash, gemini-2.5-pro, gemini-2.0-flash, gemini-2.0-flash-lite) and called them against the non-beta v1 endpoint.

What changed

• Endpoint v1 → v1beta in both GeminiProvider.ts and GeminiObservationProvider.ts — the current 3.x models and the -latest aliases are only served under v1beta.
• Model list repointed to currently-available IDs: gemini-flash-latest, gemini-flash-lite-latest, gemini-3.5-flash, gemini-3.1-flash-lite, gemini-3-flash-preview. Default is now gemini-flash-latest, a Google-maintained alias that tracks the current GA Flash model, so it won't go stale on new keys the next time Google rotates models.
• Dropped the bogus gemini-3-flash ID (only gemini-3-flash-preview exists) that the earlier code carried.
• Updated all four sync points that track the model list independently (worker provider type/allow-list, SettingsDefaultsManager + ui/viewer/constants/settings.ts, SettingsRoutes validator, ContextSettingsModal dropdown), plus tests, docs, and the built plugin/ bundles.

A retired model already saved in settings.json now falls back to the working default with a warning, auto-healing users stuck on the old broken default.

Note vs. the issue's suggestion: gemini-3.5-flash / gemini-3.1-flash-lite are real, GA model IDs (verified against Google's model docs), so they're included; gemini-3-flash (no -preview) is not a real ID and was removed.

Closes #3278

---

Created with PostHog Code from an inbox report.

[greptile-apps]

Greptile Summary

This PR updates Gemini support to use current model IDs and the beta API path. The main changes are:

• Swaps Gemini API calls from v1 to v1beta.
• Replaces retired Gemini model IDs with gemini-flash-latest, gemini-flash-lite-latest, gemini-3.5-flash, gemini-3.1-flash-lite, and gemini-3-flash-preview.
• Changes Gemini defaults in worker settings, server generation, viewer constants, and built plugin bundles.
• Updates settings validation and the model dropdown to match the new allow-list.
• Refreshes Gemini docs and tests for the new endpoint and default model.

Confidence Score: 5/5

Safe to merge with minimal risk.

The changes are narrowly scoped to Gemini endpoint constants, model allow-lists, UI options, generated bundles, docs, and matching tests. No blocking correctness or security issues were found.

No files require special attention.

T-Rex Logs

What T-Rex did

• The targeted Gemini tests rerun completed with exit code 0, reporting 11 tests passed.
• The Gemini v1beta harness ran and finished with exit code 0, printing the v1beta request URL and the retired-model fallback warning.
• TypeScript checks completed successfully for both root and viewer analyses, each with exit code 0.
• Noted the attempted capture of the targeted tests log and that Bun tests passed, but the shell wrapper exited with code 2 due to /bin/sh not supporting ${PIPESTATUS[0]}; the corrected rerun artifact is the authoritative proof.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
src/services/worker/GeminiProvider.ts	Moves worker Gemini calls to v1beta, replaces retired model IDs, and falls back invalid saved models to the new default.
src/server/generation/providers/GeminiObservationProvider.ts	Moves server-side Gemini generation to v1beta and defaults to gemini-flash-latest.
src/services/worker/http/routes/SettingsRoutes.ts	Updates settings validation to accept only the refreshed Gemini model list.
src/ui/viewer/components/ContextSettingsModal.tsx	Updates the Gemini model selector default and options.
src/shared/SettingsDefaultsManager.ts	Updates persisted settings defaults to use gemini-flash-latest.
tests/gemini_provider.test.ts	Updates Gemini provider tests for the new endpoint and model default.
plugin/scripts/worker-service.cjs	Built worker bundle reflects the v1beta endpoint, new allowed model list, and fallback default.
docs/public/usage/gemini-provider.mdx	Refreshes Gemini provider configuration docs, supported model table, and retirement note.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
participant User
participant SettingsUI as Settings UI / settings.json
participant Validator as SettingsRoutes validator
participant Worker as GeminiProvider
participant Gemini as Google Gemini v1beta

User->>SettingsUI: Select Gemini model or keep default
SettingsUI->>Validator: POST /api/settings with CLAUDE_MEM_GEMINI_MODEL
Validator-->>SettingsUI: Accept refreshed model allow-list
Worker->>SettingsUI: Load settings/defaults
alt Saved model is valid
    Worker->>Worker: Use configured model
else Saved retired/unknown model
    Worker->>Worker: Warn and fall back to gemini-flash-latest
end
Worker->>Gemini: "POST /v1beta/models/{model}:generateContent"
Gemini-->>Worker: Generated observations or provider error

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sequenceDiagram
participant User
participant SettingsUI as Settings UI / settings.json
participant Validator as SettingsRoutes validator
participant Worker as GeminiProvider
participant Gemini as Google Gemini v1beta

User->>SettingsUI: Select Gemini model or keep default
SettingsUI->>Validator: POST /api/settings with CLAUDE_MEM_GEMINI_MODEL
Validator-->>SettingsUI: Accept refreshed model allow-list
Worker->>SettingsUI: Load settings/defaults
alt Saved model is valid
    Worker->>Worker: Use configured model
else Saved retired/unknown model
    Worker->>Worker: Warn and fall back to gemini-flash-latest
end
Worker->>Gemini: "POST /v1beta/models/{model}:generateContent"
Gemini-->>Worker: Generated observations or provider error

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_{Reviews (1): Last reviewed commit: "fix(gemini): repoint providers off model..." | Re-trigger Greptile}