diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index e635e7cb..21fd34cb 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -119,7 +119,7 @@ and verify that its output is exactly `notarius v0.0.0`.
 - Invalid linker content cannot masquerade as a release version.
 - Existing CLI commands, help, streams, and exit classes remain unchanged.
 
-## Stage 2: Add One Reusable Source-Candidate Checker
+## Stage 2: Add One Reusable Source-Candidate Checker ✅
 
 ### Goal
 
diff --git a/scripts/check-release-source.sh b/scripts/check-release-source.sh
new file mode 100755
index 00000000..69df48ec
--- /dev/null
+++ b/scripts/check-release-source.sh
@@ -0,0 +1,86 @@
+#!/bin/sh
+
+set -eu
+
+fail() {
+	printf '%s\n' "check-release-source: $*" >&2
+	exit 1
+}
+
+if [ "$#" -ne 1 ]; then
+	fail "usage: $0 vMAJOR.MINOR.PATCH"
+fi
+
+release_version=$1
+if ! printf '%s\n' "$release_version" | grep -E -x 'v(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)' >/dev/null; then
+	fail "version must be a stable semantic version tag"
+fi
+
+script_dir=$(CDPATH= cd "$(dirname "$0")" && pwd)
+repo_root=$(CDPATH= cd "$script_dir/.." && pwd)
+cd "$repo_root"
+
+temporary_dir=$(mktemp -d "${TMPDIR:-/tmp}/notarius-release-source.XXXXXX") || fail "create temporary directory"
+trap 'rm -rf "$temporary_dir"' 0 HUP INT TERM
+
+if ! grep -E '^module[[:space:]]+gitea\.maximumdirect\.net/eric/notarius([[:space:]]|$)' go.mod >/dev/null; then
+	fail "go.mod does not declare the expected module path"
+fi
+
+if git ls-files --error-unmatch go.work >/dev/null 2>&1 || git ls-files --error-unmatch go.work.sum >/dev/null 2>&1; then
+	fail "tracked Go workspace files are not allowed"
+fi
+if [ -d vendor ]; then
+	fail "vendor directory is not allowed"
+fi
+if grep -E '^[[:space:]]*replace([[:space:]]|$)' go.mod >/dev/null; then
+	fail "go.mod replace directives are not allowed"
+fi
+
+GOWORK=off go test -count=1 ./...
+GOWORK=off go test -race -count=1 ./...
+GOWORK=off go vet ./...
+GOWORK=off go build ./...
+GOWORK=off go mod tidy -diff
+
+unformatted=$(git ls-files '*.go' | while IFS= read -r go_file; do
+	fmt_output=$(gofmt -l "$go_file")
+	if [ -n "$fmt_output" ]; then
+		printf '%s\n' "$fmt_output"
+	fi
+done)
+if [ -n "$unformatted" ]; then
+	printf '%s\n' "$unformatted" >&2
+	fail "tracked Go files are not gofmt formatted"
+fi
+
+git diff --check
+git diff --cached --check
+
+GOWORK=off go run ./cmd/notarius config validate --config examples/dnd-minimal.config.yml --pipeline dnd-session
+GOWORK=off OPENROUTER_API_KEY=validation-placeholder go run ./cmd/notarius config validate --config examples/dnd-complete.config.yml --pipeline dnd-session
+
+host_os=$(GOWORK=off go env GOOS)
+host_arch=$(GOWORK=off go env GOARCH)
+version_symbol='gitea.maximumdirect.net/eric/notarius/internal/buildinfo.Override'
+
+build_target() {
+	target_os=$1
+	target_arch=$2
+	target_path="$temporary_dir/notarius-$target_os-$target_arch"
+	CGO_ENABLED=0 GOOS="$target_os" GOARCH="$target_arch" GOWORK=off go build -trimpath \
+		-ldflags "-X $version_symbol=$release_version" \
+		-o "$target_path" ./cmd/notarius
+	if [ "$host_os" = "$target_os" ] && [ "$host_arch" = "$target_arch" ]; then
+		"$target_path" --version > "$temporary_dir/version-output"
+		printf 'notarius %s\n' "$release_version" > "$temporary_dir/expected-version-output"
+		if ! cmp -s "$temporary_dir/expected-version-output" "$temporary_dir/version-output"; then
+			fail "version output is incorrect for $target_os/$target_arch"
+		fi
+	fi
+}
+
+build_target linux amd64
+build_target linux arm64
+build_target darwin amd64
+build_target darwin arm64