[eersnington]

Process stdin now fails the way a Linux pipe does, the same in both clients.

Call	main	This PR
Write after the process exits	Rust: untyped invalid_state. TypeScript: OK, bytes dropped	EPIPE
Write after closeStdin	OK, bytes dropped	EBADF, from the sidecar
Spawn a process that must see EOF	Rust stream_stdin existed but nothing read it. No TypeScript option	streamStdin: false (TypeScript), stream_stdin: Some(false) (Rust)

• Closing stdin after the process exits succeeds.
• TypeScript exec ignores EPIPE when it feeds stdin to a command that exits without reading it, as echo x | true succeeds on Linux.
• The sidecar records a closed host stdin and rejects later writes with a new SidecarError::Errno, so the errno reaches the client as the error code. Both clients return it as a kernel error (code: "EBADF") and leave the process running; its wait still returns its exit code.

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This is part 4 of 6 in a stack:

•  6  fix(native-sidecar): make interactive terminals work as on Linux #2053
•  5  fix(toolchain): honor trap signal dispositions in the guest shell, as on Linux #2047
•  4  fix(runtime): give process stdin Linux semantics #2046 👈
•  3  fix(v8-runtime): log warm-pool and snapshot diagnostics through tracing #2045
•  2  fix(client): recover when a shared sidecar exits #2044
•  1  fix(native-sidecar): remove stdin, poll, and pipe stalls #2043