Why: Concurrent task worktrees reuse fixed ports and can enter an unrelated port-occupied path instead of the intended service assertion.
Evidence: An owned listener on port 18803 reproduced the existing failure; focused, parallel, and deployment fixture checks passed with the original assertions retained.
Impact: Test fixtures only; use per-instance dynamic ports and preserve restart and stolen-port checks. Full combination validation follows.
Refs: stage 6 local verification; /tmp/rdm-svc-port-isolation-report-20261014.md
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