[atiernan]

Fixes a flaky test that failed Verify (base, macOS) on #10. That PR only adds clazel-der, which this test doesn't touch.

hostile_renderers_are_killed_and_well_behaved_ones_are_unaffected (crates/clazel/tests/adversarial.rs) expected every hostile renderer to end with "closed its socket". The test sent renderer 32 a Truncated frame, and that renderer ended with "cannot write":

renderer 32 (Truncated, seed 539365443) did not end with "closed its socket": [
    "<- commit \"https://evil32.test/\" and a script of 0 bytes",
    "exited: cannot write; exit status: 0; stderr: hostile: seed=539365443 kind=Truncated bytes=8 head=0000000b82096831",
]

Cause

• hostile::attack (crates/clazel-renderer/src/hostile.rs:296-305) writes the frame and returns at once for Kind::Truncated, so that renderer exits immediately. Every other kind waits to be cut off.
• The host spawns the renderer and writes its Commit in the same step (crates/clazel/src/lib.rs:157-163), which races that exit:
  • if the host reads the closed socket first, it logs "closed its socket";
  • if the process has already exited when the host writes, the write fails, and it logs "cannot write".
• Either way the host reaps the renderer and reports RendererExited to the kernel.
• crates/clazel/tests/host.rs:108-116 already accepts both outcomes for a stub that exits immediately, for the same reason.

Fix

For the Truncated kind only, the test now accepts either wording, with a comment explaining the race. Every other kind keeps its single expected outcome. Every other assertion is unchanged:

• the renderer was sent only its Commit;
• exactly one exited line carries the right seed and kind;
• the kernel forgot the renderer;
• the well-behaved renderers match their baseline.

So a hostile renderer that wasn't cut off, or was sent more, still fails the test.

Results

• I couldn't reproduce the race locally on macOS: 0 failures in 60 idle runs and 40 under CPU load. The diagnosis comes from the code and the CI log.
• After the fix: 0 failures in 50 runs.
• cargo test -p clazel, strict clippy, cargo fmt --all --check and cargo xtask check pass.
• This changes one test file and nothing under clazel-sys, so no audit is needed.

Needs Alex's OK to merge.

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