diff --git a/appguardrail_core/rules.py b/appguardrail_core/rules.py
index c06ea203..c9a890fa 100644
--- a/appguardrail_core/rules.py
+++ b/appguardrail_core/rules.py
@@ -106,12 +106,11 @@ def as_dict(self) -> dict[str, Any]:
 
 def extract_public_references(message: str) -> tuple[str, ...]:
     """Extract OWASP, CWE, and CVE references already embedded in rule copy."""
-    return tuple(
-        dict.fromkeys(
-            " ".join(match.group(1).split())
-            for match in REFERENCE_RE.finditer(message or "")
-        )
-    )
+    seen = {}
+    if message:
+        for match in REFERENCE_RE.finditer(message):
+            seen[" ".join(match.group(1).split())] = None
+    return tuple(seen)
 
 
 def _category_for_references(references: tuple[str, ...], fallback: str) -> str:
@@ -174,8 +173,9 @@ def validate_rule_metadata(metadata: RuleMetadata | dict[str, Any]) -> list[str]
 
 
 def _merge_references(*groups: tuple[str, ...]) -> tuple[str, ...]:
-    return tuple(
-        dict.fromkeys(
-            reference for group in groups for reference in group if reference
-        )
-    )
+    seen = {}
+    for group in groups:
+        for reference in group:
+            if reference:
+                seen[reference] = None
+    return tuple(seen)
diff --git a/tests/test_reference_deduplication_contract.py b/tests/test_reference_deduplication_contract.py
new file mode 100644
index 00000000..2323ebf7
--- /dev/null
+++ b/tests/test_reference_deduplication_contract.py
@@ -0,0 +1,36 @@
+"""Regression contracts for reference extraction and ordered deduplication."""
+
+from appguardrail_core.rules import _merge_references, extract_public_references
+
+
+def test_extract_public_references_preserves_first_seen_order_and_normalizes_space() -> None:
+    """Repeated public references keep first-seen order after whitespace normalization."""
+    message = (
+        "Finding [CWE-918   - Server-Side Request Forgery] then "
+        "[OWASP A10:2021 - Server-Side Request Forgery], then "
+        "[CWE-918   - Server-Side Request Forgery] again."
+    )
+
+    assert extract_public_references(message) == (
+        "CWE-918 - Server-Side Request Forgery",
+        "OWASP A10:2021 - Server-Side Request Forgery",
+    )
+
+
+def test_extract_public_references_handles_empty_and_unmatched_messages() -> None:
+    """Messages without supported taxonomy references return an empty tuple."""
+    assert extract_public_references("") == ()
+    assert extract_public_references("plain finding without a public reference") == ()
+
+
+def test_merge_references_preserves_order_while_dropping_empty_and_duplicate_values() -> None:
+    """Merging groups keeps the first occurrence and omits empty references."""
+    assert _merge_references(
+        ("CWE-918 - Server-Side Request Forgery", "", "CWE-74 - Injection"),
+        ("CWE-918 - Server-Side Request Forgery", "OWASP A03:2021 - Injection"),
+        (),
+    ) == (
+        "CWE-918 - Server-Side Request Forgery",
+        "CWE-74 - Injection",
+        "OWASP A03:2021 - Injection",
+    )