Add Executor.stream() async generator and ModuleAnnotations.streaming

[tercel]

Summary

Add optional stream() async generator to Executor and streaming: boolean to ModuleAnnotations, enabling modules to produce incremental output.

Changes

ModuleAnnotations

• Added readonly streaming: boolean (default false)
• Updated DEFAULT_ANNOTATIONS and ANNOTATION_FIELDS

Executor.stream()

• New async *stream(moduleId, inputs?, context?): AsyncGenerator<Record<string, unknown>>
• Steps 1-6 identical to call() (context, safety, lookup, ACL, validate, before-middleware)
• If module has no stream(): falls back to call(), yields single chunk
• If module has stream(): iterates it, yields each chunk, accumulates via shallow merge
• Output validation runs on accumulated result
• After-middleware runs on accumulated result
• Error recovery via middleware onError

Extracted helper

• _validateOutput() extracted from _executeWithMiddleware() for reuse

Tests (8 new)

• Fallback single chunk, multiple chunks, ModuleNotFoundError
• Before/after middleware ordering (streaming + fallback paths)
• Error recovery, output schema validation
• Disjoint-key shallow merge accumulation

Files Changed

• src/module.ts — streaming field
• src/executor.ts — stream(), _streamWithMiddleware(), _validateOutput()
• src/schema/annotations.ts — ANNOTATION_FIELDS updated
• tests/test-executor-stream.test.ts — 8 new tests

Test Results

435 tests pass, 0 failures. tsc --noEmit clean.