fix(openapi3): emit SSE response examples on OpenAPI 3.2.0

[Yashvardhan Thanvi (Thanatos9404)]

Fixes #11090

With openapi-versions: ["3.2.0"], an @opExample on an operation that returns SSEStream<T> was missing from the output: the text/event-stream response had itemSchema but no examples, and no diagnostic was reported. With 3.0.0 or 3.1.0 the same example is emitted next to schema: { type: string }.

Cause

In getBodyContentEntry (packages/openapi3/src/openapi.ts), the 3.2.0 stream branch builds the media type with attachSSEItemSchema and returns it as soon as it is not empty. The @opExample values were only turned into example/examples after that branch, on the regular path that 3.0.0 and 3.1.0 fall through to.

Fix

Compute the examples before the stream branch and add them to the itemSchema media type as well. The example value itself is unchanged: it is the serialized body, the same string 3.0.0 and 3.1.0 already emit. OpenAPI 3.2.0 places examples next to itemSchema the same way as next to schema (section 4.14.6.2), and the JSONL example in that section also puts the whole raw stream in a single value.

The playground example from the issue now gives:

text/event-stream:
  itemSchema: {...} # unchanged by this PR
  examples:
    Example stream:
      summary: Example stream
      value: |+
        data: {"type":"message","text":"hello"}

A JsonlStream of an @events union goes through the same branch, so it keeps its examples on 3.2.0 too (checked by compiling a sample; there is no new test for it). Streams that get no itemSchema (for example a JsonlStream of a plain model) already took the regular path and are unchanged.

Tests

New tests in test/sse.test.ts compile the example from the issue:

• 3.2.0: examples is emitted next to itemSchema. This fails on main (examples is undefined) and passes with the fix.
• 3.0.0 and 3.1.0: examples is still emitted next to schema: { type: string }, with the streams-not-supported warning. These pass before and after.

The full @typespec/openapi3 test suite passes (74 files, 2706 tests). prettier --check, oxlint --type-aware --deny-warnings and cspell are clean on the changed files.

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