Add capability security failure taxonomy labels

Register four deterministic capability/security failure taxonomy labels for future fixture and artifact hardening.

Scope remains taxonomy-focused: registry, docs, and taxonomy tests only; no fixtures, generated artifacts, README, workflows, runtime/orchestration behavior, or package files changed.

Author: ProfRandom92

docs/failure_taxonomy.md

@@ -30,3 +30,22 @@ Each registered label includes:
 - `HIGH_CRITICAL_EVIDENCE_LOSS`
 
 These preferred labels are operationally defined in the canonical registry, regardless of whether a given fixture family currently emits each one.
+
+## Capability/security taxonomy expansion (registration-only)
+
+The following labels are registered for future deterministic fixture/artifact hardening, with operational semantics anchored to explicit contracts and replay evidence:
+
+- `CAPABILITY_BOUNDARY_LOSS`
+  - deterministic focus: explicit boundary preservation loss in reconstructed replay state
+  - expected evidence shape: missing boundary nodes/edges in capability-boundary contracts, fixtures, or artifacts
+- `UNAUTHORIZED_CAPABILITY_PATH`
+  - deterministic focus: explicit new capability/resource/tool path introduced in reconstruction
+  - expected evidence shape: added boundary edges or nodes that create a new path not present in allowed baseline
+- `APPROVAL_GATE_LOSS`
+  - deterministic focus: required approval/validation/human-gate commitment missing before guarded action path
+  - expected evidence shape: ordering/capability-boundary fixtures or artifacts showing absent gate precondition
+- `POLICY_ENFORCEMENT_GAP`
+  - deterministic focus: policy enforcement condition dropped while related action/dependency path remains present
+  - expected evidence shape: policy/guard contract evidence showing missing enforcement constraint with surviving action path
+
+Registration in this taxonomy does not itself change fixture expectations or generated artifacts. Any future fixture use of these labels must be backed by deterministic contracts or artifact evidence.

src/validation/failure_taxonomy.py

@@ -140,6 +140,34 @@
         "severity_class": "critical",
         "non_goal": "Not a single-run runtime fault outside deterministic replay validation.",
     },
+    "CAPABILITY_BOUNDARY_LOSS": {
+        "operational_meaning": "Reconstructed replay state no longer preserves an explicit capability, resource, or tool boundary present in the original operational state.",
+        "observable_trigger": "Capability-boundary replay contract, fixture expectation, or validator reports missing boundary nodes or boundary edges after reconstruction.",
+        "contract_or_invariant_type": "capability_boundary",
+        "severity_class": "safety",
+        "non_goal": "Not a runtime exploitability claim, live access-control verdict, or external security-breach assertion.",
+    },
+    "UNAUTHORIZED_CAPABILITY_PATH": {
+        "operational_meaning": "Reconstructed replay state introduces an explicit capability, tool, or resource path absent from the original allowed capability boundary.",
+        "observable_trigger": "Capability-boundary replay contract, fixture expectation, or validator reports added boundary edges or capability nodes that create a new explicit path.",
+        "contract_or_invariant_type": "capability_boundary",
+        "severity_class": "safety",
+        "non_goal": "Not an intent inference, exploitability judgment, or authorization conclusion derived from prose or unstated policy.",
+    },
+    "APPROVAL_GATE_LOSS": {
+        "operational_meaning": "Replay reconstruction drops an explicit approval, validation, or human-gate commitment required before a guarded action.",
+        "observable_trigger": "Fixture expectation, ordering artifact, capability-boundary artifact, or validator reports that a required approval or validation gate is missing before a guarded action path.",
+        "contract_or_invariant_type": "governance_gate",
+        "severity_class": "governance",
+        "non_goal": "Not a requirement for live human-in-the-loop runtime behavior and not a clinical, legal, or production approval claim.",
+    },
+    "POLICY_ENFORCEMENT_GAP": {
+        "operational_meaning": "Reconstructed replay state preserves an action or dependency while losing the explicit policy enforcement condition that constrained it.",
+        "observable_trigger": "Fixture expectation, policy-order contract, capability-boundary artifact, or validator reports a missing policy or guard condition while the related action path remains present.",
+        "contract_or_invariant_type": "policy_enforcement",
+        "severity_class": "governance",
+        "non_goal": "Not a live policy-engine bypass claim, external compliance assertion, or runtime exploitability determination.",
+    },
     "CONSTRAINT_DRIFT": {
         "operational_meaning": "Constraint preservation falls below full deterministic survival.",
         "observable_trigger": "constraint_survival_rate < 1.0 in replay metrics.",

tests/test_failure_taxonomy.py

@@ -76,3 +76,14 @@ def test_registered_labels_do_not_use_banned_fuzzy_terms() -> None:
         normalized = label.lower()
         for banned in BANNED_FUZZY_TERMS:
             assert banned not in normalized, f"label '{label}' contains banned fuzzy term '{banned}'"
+
+
+def test_capability_security_expansion_labels_are_registered() -> None:
+    expected_labels = {
+        "CAPABILITY_BOUNDARY_LOSS",
+        "UNAUTHORIZED_CAPABILITY_PATH",
+        "APPROVAL_GATE_LOSS",
+        "POLICY_ENFORCEMENT_GAP",
+    }
+    missing = sorted(label for label in expected_labels if label not in FAILURE_TAXONOMY)
+    assert not missing, f"expected capability/security labels missing from taxonomy: {missing}"