Core Rule Set tests: only the concurrency test runs with the race detector (closes #306)

The race pass runs TestConcurrentRequestsKeepTheirOwnExclusions alone of
internal/coreruleset's tests; every other test of the package moves to the
pass that runs the recorded requests, without the race detector. Other
packages run under -race as before. The 90-second limit stays.

Model: opus-5-5

Dockerfile

@@ -42,20 +42,35 @@ RUN go mod tidy -diff || \
 # Go's build cache is kept on a tmpfs, out of the image: nothing uses it
 # after this step, and writing it into the image takes seconds. The tests
 # are built with the no_fs_access tag, as the binary is in the build stage.
+#
+# The race detector finds bugs only in code that runs in several goroutines
+# at once. Of the Core Rule Set's tests, only
+# TestConcurrentRequestsKeepTheirOwnExclusions inspects requests that way,
+# so it is the only one of them in this pass. The second pass runs the rest.
 FROM test-setup AS test-race
 
 RUN --mount=type=tmpfs,target=/root/.cache/go-build \
-    go test -tags no_fs_access -timeout 90s -race -cover ./... || \
+    others="$(go list ./... | grep -vxF sneak.berlin/go/smallwebwaf/internal/coreruleset)"; \
+    { go test -tags no_fs_access -timeout 90s -race -cover $others && \
+      go test -tags no_fs_access -timeout 90s -race -cover \
+        -run '^TestConcurrentRequestsKeepTheirOwnExclusions$' ./internal/coreruleset; } || \
     { echo "--- Rerunning with -v for details ---"; \
-      go test -tags no_fs_access -timeout 90s -race -v ./...; exit 1; }
+      go test -tags no_fs_access -timeout 90s -race -v $others; \
+      go test -tags no_fs_access -timeout 90s -race -v \
+        -run '^TestConcurrentRequestsKeepTheirOwnExclusions$' ./internal/coreruleset; \
+      exit 1; }
 
-# Second pass: the recorded requests, too slow for make test under -race.
+# Second pass: every other test of the Core Rule Set, the recorded requests
+# among them, without the race detector.
 FROM test-setup AS test-recorded
 
 RUN --mount=type=tmpfs,target=/root/.cache/go-build \
-    go test -tags no_fs_access,recorded -timeout 90s -cover -run '^TestOrdinary' ./internal/coreruleset/... || \
+    go test -tags no_fs_access,recorded -timeout 90s -cover \
+        -skip '^TestConcurrentRequestsKeepTheirOwnExclusions$' ./internal/coreruleset || \
     { echo "--- Rerunning with -v for details ---"; \
-      go test -tags no_fs_access,recorded -timeout 90s -run '^TestOrdinary' -v ./internal/coreruleset/...; exit 1; }
+      go test -tags no_fs_access,recorded -timeout 90s -v \
+        -skip '^TestConcurrentRequestsKeepTheirOwnExclusions$' ./internal/coreruleset; \
+      exit 1; }
 
 # The test phase that script/test and the build stage name. Nothing is
 # wanted from the two passes; the copies are what make BuildKit run them.