[followup] captureLogs exists byte-identical in three packages and is t.Parallel-hostile

open   by a73x

Labels: backlog

[claude 2026-08-14] Found during T4 quality review on per-vm-networks: captureLogs (slog.SetDefault swap + t.Cleanup restore) now lives byte-identically in internal/agent/run/reservations_test.go, internal/server/api/auth_test.go, and internal/agent/netenv/named_test.go. Safe only because none of those packages call t.Parallel; the first test that adds parallelism turns it into a flaky cross-test race. Fold into the shared-test-harness work: one exported test-support home, and a guard (or doc) about the t.Parallel constraint.