5 ready fixes available as PRs (blocked from opening) #3125

I have 5 fixes ready on branches of my fork (nikolas-sapa/typescript-sdk), but PR creation to this repo is denied for my account (CreatePullRequest permission error — likely repo interaction limits).

Branches ready to submit:

• fix/streamable-http-cancellation-settlement — fixes Streamable HTTP: the POST for a cancelled request never settles #3053 (POST for cancelled request never settles)
• fix/stdio-transport-resilience — stdio transport: unhandled stderr crashes + send backpressure hangs
• fix/json-rpc-error-null-id — route uncorrelated JSON-RPC error responses to onerror
• fix/export-leaked-public-api-types — export public API callback/context types
• fix/sse-client-header-preservation — preserve Last-Event-ID + eventSourceInit headers in SSE transport

Each is a small, self-contained diff with a changeset. Happy to open the PRs if the interaction limit is lifted, or a maintainer can pull the branches directly.