Send a default User-Agent on remote MCP requests

[RhysSullivan]

Summary

Remote MCP requests (Streamable HTTP and SSE) had no User-Agent when the runtime's fetch adds none, as on Cloudflare Workers. Some servers behind Cloudflare answer those with a 403 challenge. This adds User-Agent: executor to the transport's requestInit headers when none is configured, matching the OpenAPI plugin. The SDK applies those headers to every transport request and to OAuth metadata discovery, with or without the HTTP client layer. A configured User-Agent still wins.

Tests are in #2255.

Verification

• bun run lint, bun run format:check, MCP plugin typecheck and vitest run pass.

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Torn down — the PR is closed.

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Status	Name	Latest Commit	Updated (UTC)
✅ Deployment successful! View logs	executor-cloud	675213b	Oct 10 2026, 04:36 PM

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commit: 675213b