A push to main and its version tag fire two CI runs for the same commit. Both ran `go test ./...`, which starts embedded-postgres on a FIXED port (54329/54330) and a shared data dir. -p 1 serialises packages WITHIN a run, not across two concurrent runs — so when the two runs overlapped they collided on the port/data dir and BOTH failed the Lint/Test job (no image built). Prior commits passed only because their two runs happened not to overlap. Derive the port and runtime/data dirs from the PID; share only CachePath so the PG archive downloads once. Proven: two concurrent `go test` of the store package now both pass. Unblocks the v0.21.0 (Pillar A) build. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>