refactor: remove dead code, fix silent socket option no-ops, fix tempdir leak

[danbugs]

Summary

Three cleanup items:

• FsSandbox::register duplication (~190 LOC): Deleted FsSandbox::register
  which duplicated all 9 fs handlers from FsRouter::register. Only used in
  tests — updated those to use FsRouter with a single preopen, testing the
  actual production code path.
• Silent socket option no-ops: net_setsockopt and net_getsockopt silently
  returned Ok/0 for unrecognized (level, optname) pairs. Now returns an error so
  guests can detect unsupported options.
• pptx-gen tempdir leak: inject_script_into_rootfs used
  std::mem::forget(temp_dir) to keep the returned path valid. Now returns the
  TempDir alongside the path so the caller owns the lifetime.

Test plan

• All host tests pass (tests now exercise production FsRouter path)
• cargo check passes for demos/pptx-gen

[Copilot]

Pull request overview

Cleanup PR that removes a duplicated FsSandbox::register method (~190 LOC) and updates its tests to exercise the production FsRouter code path, converts silent no-op behavior in net_setsockopt / net_getsockopt for unknown options into explicit errors, and fixes a TempDir leak in pptx-gen by returning the TempDir to the caller for proper lifetime ownership.

Changes:

• Delete dead FsSandbox::register and migrate two tests to FsRouter with a /host preopen.
• Return errors for unsupported (level, optname) pairs in net_setsockopt / net_getsockopt.
• Return (PathBuf, TempDir) from inject_script_into_rootfs instead of mem::forget-ing the TempDir.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
host/src/lib.rs	Drops FsSandbox::register duplication, updates two FS tests to use FsRouter/Preopen, and replaces silent socket-option no-ops with explicit errors.
demos/pptx-gen/src/main.rs	Returns the TempDir from inject_script_into_rootfs so the caller controls its lifetime; updates caller to bind it.

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[github-actions]

Linux Benchmarks

Details

Benchmark suite	Current: 6c578d8	Previous: 2ad29b8	Ratio
hello_world (median)	20 ms	20 ms	1
pandas (median)	100 ms	110 ms	0.91
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: 6c578d8	Previous: 2ad29b8	Ratio
hello_world (median)	255 ms	316 ms	0.81
pandas (median)	815 ms	1015 ms	0.80
density (per VM)	6 MB	6 MB	1
snapshot (disk)	393 MiB	393 MiB	1

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