fix(openapi): resolve streaming request name collision when multiple endpoints share a $ref body

[jsklan]

Description

When two endpoints both use x-fern-streaming with stream-condition and reference the same $ref request body schema, the auto-disambiguation logic (introduced in #13568) derived the streaming request name from the shared schema name (e.g., NorthChatRequestInternalStreaming). Since the name came from the $ref rather than the endpoint, multiple endpoints sharing the same request body all produced the same streaming request name, causing "NorthChatRequestInternalStreaming is already declared in this file" errors.

Changes Made

• convertStreamingOperation.ts: Removed the ${schemaId}Streaming auto-disambiguation. Now only passes through the explicit stream-request-name user override (if provided). Otherwise, convertHttpOperation's generatedRequestName — which is already unique per endpoint via breadcrumbs with a "stream" suffix — flows through as the natural fallback.
• Test fixtures: Added a second endpoint (sharing the same $ref request body) to the x-fern-streaming-with-reference fixture in both openapi-ir-to-fern-tests and v3-importer-tests to cover the multi-endpoint collision case. Also added a third endpoint without x-fern-sdk-method-name to exercise the operationId-based breadcrumb path.

Context on #13568

PR #13568 introduced the ${schemaId}Streaming auto-disambiguation to prevent streaming and non-streaming variants of a single endpoint from colliding when the request body is a $ref. We attempted to reproduce that original bug by running our updated fixture against the pre-#13568 code, but the generatedRequestName (breadcrumb-based) already produced unique names in all scenarios we tested — with and without x-fern-sdk-method-name, and with various $ref schema names. The explicit stream-request-name user override added in #13568 is preserved and still works.

Testing

• All 275 openapi-ir-to-fern-tests pass
• All 236 v3-importer-tests pass
• Verified fern check against the Cohere spec that originally triggered this bug — 0 errors (previously 1 error)

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