sanitize mcp schemas for Gemini; fix gpt-codex-mini alias; add matrix filter

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.

test/list-aliases.ts

@@ -3,7 +3,12 @@
  * matrix job. `agent` is auto-derived from the alias provider and matches the
  * harness the runtime would pick in production.
  *
- * usage: `node action/test/list-aliases.ts`
+ * set MATRIX_FILTER to a substring to restrict the matrix to matching aliases
+ * — useful for iterating on a single provider without paying for every model.
+ *
+ * usage:
+ *   node action/test/list-aliases.ts
+ *   MATRIX_FILTER=gemini node action/test/list-aliases.ts
  */
 import { modelAliases } from "../models.ts";
 
@@ -11,11 +16,15 @@ function agentForSlug(slug: string): "claude" | "opencode" {
   return slug.startsWith("anthropic/") ? "claude" : "opencode";
 }
 
-const matrix = modelAliases.map((alias) => ({
-  slug: alias.slug,
-  agent: agentForSlug(alias.slug),
-  // readable display name (GHA renders slashes awkwardly in matrix job titles)
-  name: alias.slug.replace("/", "-"),
-}));
+const filter = process.env.MATRIX_FILTER?.trim() ?? "";
+
+const matrix = modelAliases
+  .filter((alias) => (filter ? alias.slug.toLowerCase().includes(filter.toLowerCase()) : true))
+  .map((alias) => ({
+    slug: alias.slug,
+    agent: agentForSlug(alias.slug),
+    // readable display name (GHA renders slashes awkwardly in matrix job titles)
+    name: alias.slug.replace("/", "-"),
+  }));
 
 process.stdout.write(JSON.stringify(matrix));