diff --git a/.github/workflows/publish-pypi.yml b/.github/workflows/publish-pypi.yml
index cf2d302..2e5e463 100644
--- a/.github/workflows/publish-pypi.yml
+++ b/.github/workflows/publish-pypi.yml
@@ -219,9 +219,39 @@ jobs:
       AZURE_TENANT_ID: ${{ secrets.AZURE_TENANT_ID }}
       AZURE_SUBSCRIPTION_ID: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
 
+  runtime-dependency-audit:
+    name: Candidate runtime audit (Py ${{ matrix.python-version }})
+    needs: build
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.11", "3.12", "3.13", "3.14"]
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/setup-python@5fda3b95a4ea91299a34e894583c3862153e4b97 # v7.0.0
+        with:
+          python-version: ${{ matrix.python-version }}
+      - uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
+        with:
+          name: dist
+          path: candidate-dist
+      - name: Audit exact candidate runtime closure
+        run: make audit-candidate CANDIDATE_WHEEL="$(realpath candidate-dist/*.whl)"
+      - name: Verify audit guards on the selected interpreter
+        run: |
+          pip install pytest pytest-cov
+          python -m pytest -o addopts= tests/test_runtime_audit_report.py
+      - name: Retain audit inventory and scanner output
+        if: always()
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+        with:
+          name: runtime-audit-${{ matrix.python-version }}
+          path: test-results/runtime-audit/
+
   publish:
     name: Publish to PyPI
-    needs: [build, lib-tests, cookbook-smoke, cookbook-host-smoke, azure-e2e]
+    needs: [build, lib-tests, cookbook-smoke, cookbook-host-smoke, azure-e2e, runtime-dependency-audit]
     runs-on: ubuntu-latest
     environment: pypi
     permissions:
diff --git a/Makefile b/Makefile
index e9931ba..a03bd76 100644
--- a/Makefile
+++ b/Makefile
@@ -163,6 +163,10 @@ build: ensure-hatch
 host-candidate:
 	@bash scripts/check_candidate_host.sh "$(CANDIDATE_WHEEL)"
 
+.PHONY: audit-candidate
+audit-candidate:
+	@bash scripts/audit_candidate.sh "$(CANDIDATE_WHEEL)"
+
 .PHONY: publish-test
 publish-test: ensure-hatch
 	@$(HATCH) publish --repo test
diff --git a/SECURITY.md b/SECURITY.md
index ce14ebb..a9e978d 100644
--- a/SECURITY.md
+++ b/SECURITY.md
@@ -1,5 +1,25 @@
 # Security Policy
 
+## Candidate runtime advisory gate
+
+The release `runtime-dependency-audit` matrix installs the exact built wheel in a
+fresh environment on Python 3.11–3.14 and audits its resolved runtime closure.
+`make audit-candidate CANDIDATE_WHEEL=/absolute/path/to/candidate.whl` reproduces
+the gate on the current `python` interpreter. Scanner tools live in a different
+environment, so development/scanner dependencies cannot contaminate that closure.
+The unpublished candidate itself is excluded from advisory lookup; its dependencies
+are not. Runtime advisories return status 1; missing, incomplete or malformed
+reports and scanner failures return status 2. Both block publishing, with inventory
+and JSON scanner evidence uploaded even on failure. No exception mechanism is
+introduced. Development-dependency audit findings remain advisory, not a substitute
+for this exact-candidate gate.
+
+Azure host authentication belongs to the route binding, never this decorator.
+`expose_internal_errors=True` is unsafe for production: it gives custom formatters
+original server-side exceptions. Default 5xx responses and formatter fallback must
+not echo request bodies, credentials or Pydantic input. Server-side diagnostic logs
+can retain exception details and must be protected separately.
+
 ## Reporting a Vulnerability
 
 We take security seriously. If you discover a vulnerability, please report it
diff --git a/scripts/audit_candidate.sh b/scripts/audit_candidate.sh
new file mode 100644
index 0000000..d177903
--- /dev/null
+++ b/scripts/audit_candidate.sh
@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -euo pipefail
+wheel=$(realpath "${1:?candidate wheel required}")
+output="$(pwd)/test-results/runtime-audit"
+mkdir -p "$output"
+scratch=$(mktemp -d)
+trap 'rm -rf "$scratch"' EXIT
+python -m venv "$scratch/runtime"
+"$scratch/runtime/bin/python" -m pip install --disable-pip-version-check "$wheel"
+"$scratch/runtime/bin/python" -m pip check
+"$scratch/runtime/bin/python" -m pip freeze --exclude azure-functions-validation > "$output/runtime.txt"
+test -s "$output/runtime.txt"
+python -m venv "$scratch/auditor"
+"$scratch/auditor/bin/python" -m pip install --disable-pip-version-check 'pip-audit==2.10.0'
+rm -f "$output/audit.json"
+status=0
+"$scratch/auditor/bin/python" -m pip_audit --strict --no-deps --disable-pip \
+  -r "$output/runtime.txt" --format json --output "$output/audit.json" || status=$?
+python scripts/check_runtime_audit.py "$output/audit.json" "$status"
diff --git a/scripts/check_runtime_audit.py b/scripts/check_runtime_audit.py
new file mode 100644
index 0000000..502a367
--- /dev/null
+++ b/scripts/check_runtime_audit.py
@@ -0,0 +1,29 @@
+from __future__ import annotations
+
+import json
+from pathlib import Path
+import sys
+
+
+def check_report(path: Path, status: int) -> int:
+    try:
+        report = json.loads(path.read_text())
+        dependencies = report["dependencies"]
+        if not dependencies or any("skip_reason" in item for item in dependencies):
+            raise ValueError("incomplete runtime inventory")
+        findings = any(item["vulns"] for item in dependencies)
+    except (OSError, ValueError, KeyError, TypeError, AttributeError):
+        print("runtime audit tool error: missing, malformed or incomplete report", file=sys.stderr)
+        return 2
+    if status not in (0, 1) or (status == 1 and not findings):
+        print("runtime audit tool error: scanner did not complete", file=sys.stderr)
+        return 2
+    if findings:
+        print("runtime audit blocked: known runtime advisories", file=sys.stderr)
+        return 1
+    print(f"runtime audit clean: {len(dependencies)} dependencies")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(check_report(Path(sys.argv[1]), int(sys.argv[2])))
diff --git a/tests/test_runtime_audit_contract.py b/tests/test_runtime_audit_contract.py
new file mode 100644
index 0000000..33052c0
--- /dev/null
+++ b/tests/test_runtime_audit_contract.py
@@ -0,0 +1,13 @@
+from pathlib import Path
+
+import yaml
+
+
+def test_publish_requires_candidate_runtime_audit_on_all_supported_interpreters() -> None:
+    root = Path(__file__).resolve().parents[1]
+    workflow = yaml.safe_load((root / ".github/workflows/publish-pypi.yml").read_text())
+    assert "runtime-dependency-audit" in workflow["jobs"]["publish"]["needs"]
+    job = workflow["jobs"]["runtime-dependency-audit"]
+    assert job["strategy"]["matrix"]["python-version"] == ["3.11", "3.12", "3.13", "3.14"]
+    assert any("make audit-candidate" in step.get("run", "") for step in job["steps"])
+    assert any(step.get("if") == "always()" for step in job["steps"])
diff --git a/tests/test_runtime_audit_report.py b/tests/test_runtime_audit_report.py
new file mode 100644
index 0000000..d411123
--- /dev/null
+++ b/tests/test_runtime_audit_report.py
@@ -0,0 +1,34 @@
+import json
+from pathlib import Path
+from typing import Any
+
+import pytest
+
+from scripts.check_runtime_audit import check_report
+
+
+@pytest.mark.parametrize(
+    ("report", "status", "expected"),
+    [
+        ({"dependencies": [{"name": "dep", "vulns": []}]}, 0, 0),
+        ({"dependencies": [{"name": "dep", "vulns": [{"id": "CVE-test"}]}]}, 1, 1),
+        ({"dependencies": []}, 0, 2),
+        ({"dependencies": [None]}, 0, 2),
+        ({"dependencies": [{"name": "dep", "skip_reason": "unknown"}]}, 0, 2),
+        ({"dependencies": [{"name": "dep", "vulns": []}]}, 1, 2),
+        ({"dependencies": [{"name": "dep", "vulns": []}]}, 2, 2),
+    ],
+)
+def test_audit_report_distinguishes_advisories_from_tool_errors(
+    tmp_path: Path, report: dict[str, Any], status: int, expected: int
+) -> None:
+    path = tmp_path / "audit.json"
+    path.write_text(json.dumps(report))
+    assert check_report(path, status) == expected
+
+
+def test_missing_and_unparsable_audit_fail_closed(tmp_path: Path) -> None:
+    path = tmp_path / "missing.json"
+    assert check_report(path, 0) == 2
+    path.write_text("not JSON")
+    assert check_report(path, 0) == 2
diff --git a/tests/test_security_boundary_proofs.py b/tests/test_security_boundary_proofs.py
new file mode 100644
index 0000000..db97f7c
--- /dev/null
+++ b/tests/test_security_boundary_proofs.py
@@ -0,0 +1,60 @@
+import json
+
+import azure.functions as func
+from pydantic import BaseModel
+import pytest
+
+from azure_functions_validation import HttpError, validate_http
+from azure_functions_validation.testing import MockHttpRequest
+
+
+class Response(BaseModel):
+    value: int
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize("helper", [False, True])
+@pytest.mark.parametrize("formatter_fails", [False, True])
+async def test_default_5xx_and_failing_formatter_never_echo_input_or_credentials(
+    asynchronous: bool, helper: bool, formatter_fails: bool
+) -> None:
+    secret = "CANARY-secret-credential-input"
+
+    def formatter(exc: Exception, status: int) -> dict[str, str]:
+        raise RuntimeError(secret)
+
+    def handler(req: func.HttpRequest) -> dict[str, str]:
+        return {"value": secret}
+
+    async def async_handler(req: func.HttpRequest) -> dict[str, str]:
+        return handler(req)
+
+    wrapped = validate_http(
+        response_model=Response, error_formatter=formatter if formatter_fails else None
+    )(async_handler if asynchronous else handler)
+    request_type = MockHttpRequest if helper else func.HttpRequest
+    request = request_type(
+        method="POST",
+        url="https://example.test",
+        body=secret.encode(),
+        headers={"Authorization": secret},
+    )
+    response = await wrapped(request) if asynchronous else wrapped(request)
+    assert response.status_code == 500
+    assert secret not in response.get_body().decode()
+    assert secret not in repr(dict(response.headers))
+
+
+@pytest.mark.parametrize("auth", [func.AuthLevel.FUNCTION, func.AuthLevel.ADMIN])
+def test_validation_preserves_host_owned_authentication(auth: func.AuthLevel) -> None:
+    app = func.FunctionApp(http_auth_level=func.AuthLevel.ANONYMOUS)
+
+    @app.route(route="protected", auth_level=auth)
+    @validate_http()
+    def handler(req: func.HttpRequest) -> None:
+        raise HttpError(500, "private")
+
+    bindings = json.loads(app.get_functions()[0].get_function_json())["bindings"]
+    trigger = next(binding for binding in bindings if binding["type"] == "httpTrigger")
+    assert trigger["authLevel"].casefold() == auth.value