diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index fc2b269..440f77e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -118,6 +118,13 @@ jobs:
       - name: Run tests
         run: make test
 
+      # The withsidecar-tagged tests had never been compiled into a test
+      # binary: the tag appears only under go build, go install and go run.
+      # They cover the embedded JAR's extraction, checksum reuse and the
+      # concurrent-extraction race, so they need the staged JAR to be real.
+      - name: Run the sidecar-tagged tests
+        run: make test-sidecar
+
       # folio is its own gradle build, and the metro plugin it compiles with
       # needs a 21 runtime where the sidecar toolchain pins 17. Switching
       # JAVA_HOME after `make test` rather than installing both up front
@@ -266,6 +273,13 @@ jobs:
       - name: Build sanderling
         run: make sanderling-ios
 
+      # The withcompanion-tagged tests are reachable only through this target
+      # and no other job invokes it. It runs here because staging the companion
+      # and runner bundles needs the darwin toolchain, and make sanderling-ios
+      # has already built both.
+      - name: Run the companion-tagged tests
+        run: make test-companion
+
       # simctl resolves a device by name alone, and one image carries the same
       # phone under several runtimes: iPhone 17 Pro exists here on iOS 26.2,
       # 26.4 and 26.5. Booting by name is therefore booting on whichever one
diff --git a/Makefile b/Makefile
index b892ee8..6045873 100644
--- a/Makefile
+++ b/Makefile
@@ -29,7 +29,7 @@ WEB_DIST := replay-ui/dist
 
 GOLINES := $(shell $(GO) env GOPATH)/bin/golines
 
-.PHONY: bootstrap proto sidecar sidecar-embed sanderling build sanderling-web sanderling-android sanderling-ios install test test-go test-browser test-companion test-kotlin test-folio test-spec-api test-ci-scripts spec-typecheck web-test web-typecheck web-build web-dev replay-dev docs clean release-cli release-npm-dry fmt fmt-go fmt-kotlin fmt-ts fmt-swift
+.PHONY: bootstrap proto sidecar sidecar-embed sanderling build sanderling-web sanderling-android sanderling-ios install test test-go test-browser test-companion test-sidecar test-kotlin test-folio test-spec-api test-ci-scripts spec-typecheck web-test web-typecheck web-build web-dev replay-dev docs clean release-cli release-npm-dry fmt fmt-go fmt-kotlin fmt-ts fmt-swift
 
 bootstrap:
 	$(GO) mod download
@@ -148,6 +148,13 @@ test-browser:
 test-companion: $(COMPANION_EMBED) $(RUNNER_EMBED)
 	$(GO) test -tags withcompanion ./internal/driver/ioscompanion/...
 
+# Runs the withsidecar-tagged tests (embedded size, extraction, checksum reuse
+# and the concurrent-extraction race) against the real JAR. Kept out of `test`
+# because staging the JAR needs the android toolchain. Untagged, the package
+# builds against the stub and these never compile.
+test-sidecar: $(SIDECAR_EMBED)
+	$(GO) test -tags withsidecar ./internal/sidecarassets/...
+
 test-kotlin:
 	ANDROID_HOME=$(ANDROID_HOME) $(GRADLE) :sidecar:test