diff --git a/decnet/web/_uvicorn_tls_scope.py b/decnet/web/_uvicorn_tls_scope.py
new file mode 100644
index 0000000..f68ad56
--- /dev/null
+++ b/decnet/web/_uvicorn_tls_scope.py
@@ -0,0 +1,72 @@
+"""Inject the TLS peer cert into ASGI scope — uvicorn ≤ 0.44 does not.
+
+Uvicorn's h11/httptools HTTP protocols build the ASGI ``scope`` dict
+without any ``extensions.tls`` entry, so per-request cert pinning
+handlers (like POST /swarm/heartbeat) can't see the client cert that
+CERT_REQUIRED already validated at handshake.
+
+We patch ``RequestResponseCycle.__init__`` on both protocol modules to
+read the peer cert off the asyncio transport (which *does* carry it)
+and write the DER bytes into
+``scope["extensions"]["tls"]["client_cert_chain"]``. This is the same
+key the ASGI TLS extension proposal uses, so the application code will
+keep working unchanged if a future uvicorn populates it natively.
+
+Import this module once at app startup time (before uvicorn starts
+accepting connections). Idempotent — subsequent imports are no-ops.
+"""
+from __future__ import annotations
+
+from typing import Any
+
+
+_PATCHED = False
+
+
+def _wrap_cycle_init(cycle_cls) -> None:
+    original = cycle_cls.__init__
+
+    def _patched_init(self, *args: Any, **kwargs: Any) -> None:
+        original(self, *args, **kwargs)
+        transport = kwargs.get("transport") or getattr(self, "transport", None)
+        if transport is None:
+            return
+        ssl_obj = transport.get_extra_info("ssl_object")
+        if ssl_obj is None:
+            return
+        try:
+            der = ssl_obj.getpeercert(binary_form=True)
+        except Exception:
+            return
+        if not der:
+            return
+        # scope is a mutable dict uvicorn stores here; Starlette forwards
+        # it to handlers as request.scope. Use setdefault so we don't clobber
+        # any future native extension entries from uvicorn itself.
+        scope = self.scope
+        extensions = scope.setdefault("extensions", {})
+        extensions.setdefault("tls", {"client_cert_chain": [der]})
+
+    cycle_cls.__init__ = _patched_init
+
+
+def install() -> None:
+    """Patch uvicorn's HTTP cycle classes. Safe to call multiple times."""
+    global _PATCHED
+    if _PATCHED:
+        return
+    try:
+        from uvicorn.protocols.http import h11_impl
+        _wrap_cycle_init(h11_impl.RequestResponseCycle)
+    except Exception:  # nosec B110 - optional uvicorn impl may be unavailable
+        pass
+    try:
+        from uvicorn.protocols.http import httptools_impl
+        _wrap_cycle_init(httptools_impl.RequestResponseCycle)
+    except Exception:  # nosec B110 - optional uvicorn impl may be unavailable
+        pass
+    _PATCHED = True
+
+
+# Auto-install on import so simply importing this module patches uvicorn.
+install()
diff --git a/decnet/web/swarm_api.py b/decnet/web/swarm_api.py
index 669252c..43ffeb6 100644
--- a/decnet/web/swarm_api.py
+++ b/decnet/web/swarm_api.py
@@ -16,6 +16,8 @@ shared DB.
 """
 from __future__ import annotations
 
+from decnet.web import _uvicorn_tls_scope  # noqa: F401  # patches uvicorn on import
+
 from contextlib import asynccontextmanager
 from typing import AsyncGenerator
 
diff --git a/tests/swarm/test_uvicorn_tls_scope.py b/tests/swarm/test_uvicorn_tls_scope.py
new file mode 100644
index 0000000..d15f95d
--- /dev/null
+++ b/tests/swarm/test_uvicorn_tls_scope.py
@@ -0,0 +1,77 @@
+"""Regression tests for the uvicorn TLS scope monkey-patch."""
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+
+class _FakeSSLObject:
+    def __init__(self, der: bytes) -> None:
+        self._der = der
+
+    def getpeercert(self, binary_form: bool = False) -> bytes:
+        assert binary_form is True
+        return self._der
+
+
+class _FakeTransport:
+    def __init__(self, ssl_obj: Any = None) -> None:
+        self._ssl = ssl_obj
+
+    def get_extra_info(self, key: str) -> Any:
+        if key == "ssl_object":
+            return self._ssl
+        return None
+
+
+def _make_cycle_cls():
+    class Cycle:
+        def __init__(self, scope: dict, transport: Any = None) -> None:
+            self.scope = scope
+            self.transport = transport
+    return Cycle
+
+
+def test_wrap_cycle_injects_cert_into_scope() -> None:
+    from decnet.web._uvicorn_tls_scope import _wrap_cycle_init
+
+    Cycle = _make_cycle_cls()
+    _wrap_cycle_init(Cycle)
+
+    scope: dict = {"type": "http"}
+    transport = _FakeTransport(_FakeSSLObject(b"\x30\x82der"))
+    Cycle(scope, transport=transport)
+
+    assert scope["extensions"]["tls"]["client_cert_chain"] == [b"\x30\x82der"]
+
+
+def test_wrap_cycle_noop_when_no_ssl() -> None:
+    from decnet.web._uvicorn_tls_scope import _wrap_cycle_init
+
+    Cycle = _make_cycle_cls()
+    _wrap_cycle_init(Cycle)
+
+    scope: dict = {"type": "http"}
+    Cycle(scope, transport=_FakeTransport(ssl_obj=None))
+
+    assert "extensions" not in scope or "tls" not in scope.get("extensions", {})
+
+
+def test_wrap_cycle_noop_when_empty_der() -> None:
+    from decnet.web._uvicorn_tls_scope import _wrap_cycle_init
+
+    Cycle = _make_cycle_cls()
+    _wrap_cycle_init(Cycle)
+
+    scope: dict = {"type": "http"}
+    Cycle(scope, transport=_FakeTransport(_FakeSSLObject(b"")))
+
+    assert "extensions" not in scope or "tls" not in scope.get("extensions", {})
+
+
+def test_install_is_idempotent() -> None:
+    from decnet.web import _uvicorn_tls_scope as mod
+
+    mod.install()
+    mod.install()  # second call must not double-wrap