The previous sanitizer proxied `schema.toJsonSchema()`, but fastmcp 3.x uses
`xsschema.toJsonSchema()` which reads `schema["~standard"].jsonSchema.input(...)`
directly when the StandardJSONSchemaV1 extension is present (arktype 2.x).
Our proxy was never invoked, so the sanitizer was a silent no-op.
Proxy the entire `~standard` → `jsonSchema` → `input` chain so the transform
runs regardless of which path xsschema picks. Also add case 1 (add `type:"string"`
to enum-only schemas) — arktype 2.x emits `{enum:["A","B"]}` without a type
field, which is the exact form Gemini rejects with
"only allowed for STRING type".
Verified locally: wrapped schema now emits `{type:"string", enum:[...]}` and
drops `$schema`; validation still works.
Gemini's generateContent API rejects arktype's `{anyOf:[{enum:[...]}]}` string-enum
encoding, `$schema` metadata, and `anyOf` with sibling fields. Port the old
sanitizer back as an isolated module (action/mcp/geminiSanitizer.ts) and gate it
on `isGeminiRouted(ctx)` so non-gemini routes see the original schema. Wires
`resolvedModel` onto ToolContext so the sanitizer can see the upstream specifier.
Also bumps `openai/gpt-codex-mini` alias from the deprecated `codex-mini-latest`
to `gpt-5.1-codex-mini`, matching the openrouter resolve.
Adds a `filter` workflow_dispatch input + MATRIX_FILTER env that restricts the
models-live matrix to aliases matching a substring, so we can iterate on a
single provider (e.g. `filter=gemini`) without paying to run every model.
Colin McDonnell