[Fix] Fast turns fail with integration tool schema errors

[roomote-roomote]

​Opened on behalf of @daniel-lxs. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

Fast's integration-call wrapper now emits concrete, non-recursive JSON value alternatives instead of z.json(). Nested arrays and objects remain unrestricted on the wire and recursively validated by the unchanged server-side schema. Integration lookup, required identifiers, optional arguments, and the shared MCP schema are unchanged.

Regression tests load the generated native modules, apply OpenCode's registry normalization, serialize the result, and compile every native tool schema with Ajv Draft 2020-12. They also cover nested JSON round trips and a recursive negative control.

Why this change was made

#2237 introduced z.json() in Fast to avoid unconstrained argument schemas collapsing downstream. OpenCode 1.18.10 converts that to Draft 2020-12, then renames $defs to definitions without updating #/$defs/... references. The resulting schema cannot resolve its own references. The prior test checked raw Zod output before that rename and therefore missed the regression.

The fix preserves concrete JSON value types without depending on recursive references or reverting #2237.

Impact

Removes the malformed Fast integration wrapper schema introduced in v1.3.1. No runtime dependency upgrade, deployment, or database change is included; Ajv is test-only and already present in the lockfile.

The new tests failed against the original implementation with can't resolve reference #/$defs/__schema0 and pass with the fix. All 258 focused Fast tests pass on the current base, as do package TypeScript checks and the full pre-push lint, fast typecheck, and knip gates. One unrelated widget test timed out while competing with the full pre-push checks; the same suite passed on rerun without source changes.

An isolated OpenCode 1.18.10 process loaded the exact generated module and returned a reference-free schema from /experimental/tool; Ajv and Effect conversion accepted it and preserved nested arguments. This verifies the serialization boundary, not live provider acceptance or the exact downstream HTTP 400 stack. Browser proof is not applicable to this non-visual change.

[roomote-community]

No code issues found. See task

_{Reviewed b511ec6}