Two CI flakes surfaced on PR NousResearch#34572 (both in files this PR doesn't touch;
pre-existing host-dependent flakes):

1. test_process_registry::TestPopenLeakOnSetupFailure — the failure-cleanup
   tests use a fake proc.pid (8888/9999) and assert proc.kill() runs. But
   spawn_local's primary cleanup is os.killpg(os.getpgid(pid), SIGKILL),
   falling back to proc.kill() only on ProcessLookupError/PermissionError/
   OSError. When the fake PID happens to exist on a busy host, os.getpgid
   succeeds, os.killpg fires against an UNRELATED real process group, and
   proc.kill() is never reached -> flaky AssertionError (and a real risk of
   SIGKILLing an innocent process group from a unit test). Patch os.getpgid
   to raise ProcessLookupError so the fallback path runs deterministically
   and no real killpg is ever issued.

2. test_web_server::test_resize_escape_is_forwarded — the receive loop calls
   the blocking conn.receive_bytes() with no exception guard. Once the child
   prints its winsize and exits, the PTY closes; on a missed-marker run the
   next recv blocks until the 30s pytest-timeout instead of failing fast.
   Add a try/except break (matching the working sibling tests) and bump the
   child's pre-read sleep 0.15s -> 0.5s so the resize reliably lands first.

Verified: 4/4 pass across 3 consecutive runs; root cause for NousResearch#1 reproduced
(os.getpgid(1) succeeds -> old code skips proc.kill).

Two CI flakes surfaced on PR NousResearch#34572 (both in files this PR doesn't touch;
pre-existing host-dependent flakes):

1. test_process_registry::TestPopenLeakOnSetupFailure — the failure-cleanup
   tests use a fake proc.pid (8888/9999) and assert proc.kill() runs. But
   spawn_local's primary cleanup is os.killpg(os.getpgid(pid), SIGKILL),
   falling back to proc.kill() only on ProcessLookupError/PermissionError/
   OSError. When the fake PID happens to exist on a busy host, os.getpgid
   succeeds, os.killpg fires against an UNRELATED real process group, and
   proc.kill() is never reached -> flaky AssertionError (and a real risk of
   SIGKILLing an innocent process group from a unit test). Patch os.getpgid
   to raise ProcessLookupError so the fallback path runs deterministically
   and no real killpg is ever issued.

2. test_web_server::test_resize_escape_is_forwarded — the receive loop calls
   the blocking conn.receive_bytes() with no exception guard. Once the child
   prints its winsize and exits, the PTY closes; on a missed-marker run the
   next recv blocks until the 30s pytest-timeout instead of failing fast.
   Add a try/except break (matching the working sibling tests) and bump the
   child's pre-read sleep 0.15s -> 0.5s so the resize reliably lands first.

Verified: 4/4 pass across 3 consecutive runs; root cause for NousResearch#1 reproduced
(os.getpgid(1) succeeds -> old code skips proc.kill).

(cherry picked from commit 1c53d39)