fix(sdk-typescript): type safety and backpressure handling

[jdmanring]

Summary

Fixes for sdk-typescript package:

• C-04: Made isControlCancel type guard runtime-safe (request_id optional but guard required it)
• C-05: Replaced unsafe as never cast with proper discriminated union typing
• H-19: Fixed ProcessTransport backpressure handling (write() returns false)

Files Changed

• packages/sdk-typescript/src/types/protocol.ts
• packages/sdk-typescript/src/query/Query.ts
• packages/sdk-typescript/src/transport/ProcessTransport.ts

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Refactor
• New feature
• Breaking change

Testing

• Unit tests pass
• Integration tests pass