[fjtrujy]

Summary

• Correct the remote destination file descriptor check in fsclient_copyto.
• Validate ps2netfs path lengths and read response sizes before using buffers.
• Handle partial reads/writes, unexpected EOF, and file closure on error paths.
• Truncate overwritten local and remote destination files.
• Correct PS2HOSTNAME= matching and missing copy arguments.
• Add a native C fake-ps2netfs loopback test (tests/fsclient_smoke.c) covering short reads, short writes, and oversized responses.

Plain C / compatibility

• Based directly on master (which already includes merged PR ps2client: Migrate Python test tooling to plain C #32).
• Exactly one C-only commit; no Python code or runtime dependency.
• Existing fsclient command syntax and ps2netfs protocol are unchanged.

Validation

• make all check: passed on macOS (five C smoke checks, three new C transfer checks).
• git diff --check: passed.
• Real PS2/ps2netfs transfer testing remains recommended before merge.