fix: harden fs and net handlers

[danbugs]

Summary

• Set read/write timeouts on accepted sockets — accept() returns a new socket that doesn't inherit parent timeouts, leaving net_recv on accepted connections able to block the host thread indefinitely
• Cap fs_write_bytes offset to MAX_TRUNCATE_LEN (1 GiB) — previously a guest could pass multi-TB offsets to create sparse files, circumventing the truncate cap
• Add MAX_DIR_ENTRIES (100k) cap to fs_list to prevent host OOM on directories with millions of entries
• Guard fs_unlink against deleting the mount root directory itself

Test plan

• cargo test --lib passes (56 tests)
• cargo clippy clean
• cargo fmt clean
• CI validates no regressions

[Copilot]

Pull request overview

This PR hardens host-side filesystem and networking RPC handlers to reduce guest-driven resource exhaustion and prevent host-thread stalls during socket I/O. It fits into the host crate’s tool/handler layer where guest calls are translated into constrained host operations.

Changes:

• Set read/write timeouts on sockets returned by accept() so accepted connections can’t block host threads indefinitely.
• Add caps/guards in filesystem handlers: limit fs_list directory enumeration size, reject oversized fs_write_bytes offsets, and prevent fs_unlink from removing the mount root.

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[github-actions]

Linux Benchmarks

Details

Benchmark suite	Current: 0dcbe53	Previous: 4c053f6	Ratio
hello_world (median)	20 ms	20 ms	1
pandas (median)	110 ms	90 ms	1.22
density (per VM)	7 MB	7 MB	1
snapshot (disk)	385 MiB	385 MiB	1

This comment was automatically generated by workflow using github-action-benchmark.

[github-actions]

Windows Benchmarks

Details

Benchmark suite	Current: 0dcbe53	Previous: 4c053f6	Ratio
hello_world (median)	272 ms	181 ms	1.50
pandas (median)	876 ms	557 ms	1.57
density (per VM)	6 MB	6 MB	1
snapshot (disk)	392 MiB	392 MiB	1

This comment was automatically generated by workflow using github-action-benchmark.