fix: allow opting out of response_format strict mode (#483)

[robert-j-y]

Description

Fixes #483 by adding a new structuredOutputs.strict setting that lets users opt out of response_format.json_schema.strict per chat model.

Problem

src/chat/index.ts hardcoded strict: true whenever a JSON schema response format was used:

response_format:
  responseFormat?.type === 'json'
    ? responseFormat.schema != null
      ? {
          type: 'json_schema',
          json_schema: {
            schema: responseFormat.schema,
            strict: true, // <-- hardcoded, no override
            name: responseFormat.name ?? 'response',
            ...(responseFormat.description && { description: responseFormat.description }),
          },
        }
      : { type: 'json_object' }
    : undefined,

There was no provider-setting, no call-site option, and no way for a user to opt out. For models whose downstream providers don't implement strict json_schema (e.g. moonshotai/kimi-k2.6 routed through Parasail/Venice/Io Net), OpenRouter returned HTTP 404 "No endpoints available matching your guardrail restrictions and data policy" because the strict flag eliminated every eligible endpoint.

Fix

Added a new optional structuredOutputs?: { strict?: boolean } field to OpenRouterChatSettings. When present, its strict value is forwarded to response_format.json_schema.strict. When omitted, the SDK continues to default to true (backward compatible).

Before

const model = openrouter.chat('moonshotai/kimi-k2.6');
// SDK always sends strict: true → 404 if provider doesn't support it

After

// Default behavior unchanged — strict: true
const defaultModel = openrouter.chat('moonshotai/kimi-k2.6');

// Opt out for providers that don't support strict mode
const relaxed = openrouter.chat('moonshotai/kimi-k2.6', {
  structuredOutputs: { strict: false },
});

// Explicit opt-in still works
const explicit = openrouter.chat('moonshotai/kimi-k2.6', {
  structuredOutputs: { strict: true },
});

Implementation notes

• src/chat/index.ts:145 — replaced the hardcoded strict: true with this.settings.structuredOutputs?.strict ?? true.
• src/types/openrouter-chat-settings.ts — added the structuredOutputs?: { strict?: boolean } setting alongside other top-level chat settings.
• src/completion/index.ts — verified there is no response_format.json_schema branch (the legacy completion path forwards responseFormat directly without setting strict), so no mirror change was needed.
• Existing should pass responseFormat for JSON schema structured outputs and should use default name when name is not provided in responseFormat tests in src/chat/index.test.ts continue to assert strict: true and pass without modification — the default is preserved.

Tests

Added e2e/issues/issue-483-response-format-strict-option.test.ts with 8 cases covering:

1. Default (no setting) → strict: true (backward compat)
2. structuredOutputs: { strict: false } → strict: false
3. structuredOutputs: { strict: true } → strict: true
4. structuredOutputs: { strict: undefined } → default true
5. structuredOutputs: {} (empty object) → default true
6. Strict override preserves name and description
7. No response_format emitted when call has no responseFormat, regardless of structuredOutputs
8. responseFormat: { type: 'json' } (no schema) still emits json_object, no strict, no json_schema

Verified the failing-on-main subset of these tests reproduce the bug before applying the fix (2/8 fail on main, all 8 pass on this branch).

Human review checklist

Verified against the diff at HEAD:

• Default behavior is preserved: chat(model) with no structuredOutputs setting still emits strict: true (existing tests in src/chat/index.test.ts are unmodified and continue to pass; default-case test in the new file confirms it explicitly).
• No type assertions / as casts in the new test file (per repo no-casting rule).
• The public type addition (OpenRouterChatSettings.structuredOutputs) is the right shape — option lives on the chat settings, mirrors reasoning / plugins placement, and is documented with TSDoc.
• No existing test in src/chat/index.test.ts was modified — git diff --merge-base origin/main -- src/chat/index.test.ts is empty.
• Changeset is minor (new public setting = small feature).

Checklist

• I have run pnpm stylecheck and pnpm typecheck
• I have run pnpm test and all tests pass (421 passed)
• I have added tests for my changes (e2e/issues/issue-483-response-format-strict-option.test.ts, 8 cases — all pass; the two strict: false cases failed on main as expected before the fix)
• I have updated documentation (TSDoc on the new structuredOutputs setting)

Changeset

• I have run pnpm changeset to create a changeset file (minor)