diff --git a/tests/conformance/README.md b/tests/conformance/README.md
index 08ad059..cf03ec8 100644
--- a/tests/conformance/README.md
+++ b/tests/conformance/README.md
@@ -101,3 +101,4 @@ Spec: [trace-a2a-profile.md](../../docs/spec/trace-a2a-profile.md), [provenance-
 | ACTION-005 | MUST | A requested action outside the effective delegated scope is classified as authorization-invalid, not malformed provenance. | `SCOPE_NOT_PERMITTED`. |
 | ACTION-006 | MUST | A valid delegated action denied by local policy is classified as authorization-invalid, not malformed provenance. | `SCOPE_NOT_PERMITTED`. |
 | ACTION-007 | MUST | A valid delegated action whose controller outcome is negative remains valid evidence of a negative outcome. | `valid_negative_outcome`. |
+| ACTION-008 | MUST | An action whose delegation chain contains a credential with an invalid signature is rejected as provenance-invalid before authorization or outcome handling. | `INVALID_CREDENTIAL`. |
diff --git a/tests/conformance/test_profile_conformance.py b/tests/conformance/test_profile_conformance.py
index b923bec..09fd14a 100644
--- a/tests/conformance/test_profile_conformance.py
+++ b/tests/conformance/test_profile_conformance.py
@@ -5,7 +5,7 @@
 
 from __future__ import annotations
 
-from dataclasses import dataclass
+from dataclasses import dataclass, replace
 
 import pytest
 from cryptography.hazmat.primitives.asymmetric import ec
@@ -404,3 +404,34 @@ def test_action_007_controller_rejection_is_valid_negative_outcome() -> None:
         LocalPolicy.of(["robot.move"]),
     )
     assert result == _ActionEvidenceResult("valid_negative_outcome", "CONTROLLER_REJECTED")
+
+
+def test_action_008_invalid_delegation_signature_is_provenance_invalid() -> None:
+    chain = _action_chain()
+    records = _records(chain)
+    leaf = chain[-1]
+    tampered_signature = f"{int(leaf.signature[:2], 16) ^ 1:02x}{leaf.signature[2:]}"
+    bad_chain = [*chain[:-1], replace(leaf, signature=tampered_signature)]
+    evidence = _action_evidence(
+        records,
+        requested_capability="robot.inspect",
+        controller_decision="rejected",
+    )
+    restrictive_policy = LocalPolicy.of(["robot.move"])
+    permissive_policy = LocalPolicy.of(["robot.move", "robot.inspect"])
+
+    # The controls establish both downstream classifications that invalid provenance must preempt.
+    assert _verify_action_evidence(chain, records, evidence, restrictive_policy) == (
+        _ActionEvidenceResult("authorization_invalid", "SCOPE_NOT_PERMITTED")
+    )
+    assert _verify_action_evidence(chain, records, evidence, permissive_policy) == (
+        _ActionEvidenceResult("valid_negative_outcome", "CONTROLLER_REJECTED")
+    )
+
+    # ACTION-008 verifies provenance validation precedes authorization and controller outcome classification.
+    assert _verify_action_evidence(bad_chain, records, evidence, restrictive_policy) == (
+        _ActionEvidenceResult("provenance_invalid", "INVALID_CREDENTIAL")
+    )
+    assert _verify_action_evidence(bad_chain, records, evidence, permissive_policy) == (
+        _ActionEvidenceResult("provenance_invalid", "INVALID_CREDENTIAL")
+    )