feat(ai-sdk): stream tool outputs for async generator handlers

[dinwwwh]

createToolFactory now streams tool outputs whenever the procedure handler is an async function*, not only when the output schema is built with asyncIteratorObject. Previously a schema-less async generator handler (or one paired with a type<AsyncIteratorObject<...>>() schema) returned the iterator object as the tool result instead of streaming preliminary results, even though the inferred tool output type was already the yield type.

The detection lives in @orpc/shared as isAsyncGeneratorFunction, so other packages can reuse it.

Fixes

• Async generator handlers stream each event as a preliminary tool result with or without an asyncIteratorObject output schema. Runtime behavior now matches the inferred InferToolOutput type.
• Output schemas remain the source of truth; the handler check is a fallback, so plain async handlers that happen to return an iterator are unchanged.

Testing

• New unit tests for isAsyncGeneratorFunction (bound functions and async generator methods included, sync generators and plain async functions excluded).
• New AI SDK tests: streaming without an output schema, streaming with a non-asyncIteratorObject schema, and no streaming for a non-generator handler returning an iterator. Type test covers the schema-less yield type inference.
• Docs "Streaming Tool Outputs" section mentions the async function* path.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[codspeed-hq]

Merging this PR will not alter performance

✅ 30 untouched benchmarks

---

_{Comparing dinwwwh:claude/async-generator-check-bfd26e (537e5ea) with main (0cd296a)}

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commit: 537e5ea

[pullfrog]

✅ No new issues found.

Reviewed changes — Reviewed the full single-commit diff of feat(ai-sdk): stream tool outputs for async generator handlers (features, tests, type tests, and docs).

• isAsyncGeneratorFunction in @orpc/shared — detects native async function* handlers via the built-in constructor; correctly handles bound functions and async generator methods, and excludes sync generators, plain async functions, and iterator values (the (async function* () {})() case).
• createToolFactory streaming fallback — isIteratorOutput now also fires when the procedure handler is an async generator, so schema-less (and type<AsyncIteratorObject<...>>()-schematized) async generator handlers stream each event through the existing yield* await call(...) path instead of returning the raw iterator. Contract-based implementToolFactory is untouched.
• Tests — streaming tests genuinely fail without the fix (for await over the old Promise-returning execute throws "not async iterable", verified empirically), and the non-generator test guards against over-broad detection. The getIteratorYieldSchemas(...) branch and the handler fallback are independently exercised.
• Type test — pins InferToolOutput to the yield type for a schema-less async generator handler, matching the new runtime behavior.
• Docs — the Streaming Tool Outputs sentence now names the async function* path.

Verified: affected unit tests pass, tsc -b (incl. .test-d.ts) passes, and eslint on the changed files is clean.

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