diff --git a/decnet/profiler/behavioral.py b/decnet/profiler/behavioral.py
index bd19acc..db44648 100644
--- a/decnet/profiler/behavioral.py
+++ b/decnet/profiler/behavioral.py
@@ -314,12 +314,24 @@ def detect_tools_from_headers(events: list[LogEvent]) -> list[str]:
         if not raw_headers:
             continue
 
-        # headers may arrive as a JSON string or a dict already
+        # headers may arrive as a JSON string, a Python-repr string (legacy),
+        # or a dict already (in-memory / test paths).
         if isinstance(raw_headers, str):
             try:
                 headers: dict[str, str] = json.loads(raw_headers)
             except (json.JSONDecodeError, ValueError):
-                continue
+                # Backward-compat: events written before the JSON-encode fix
+                # were serialized as Python repr via str(dict).  ast.literal_eval
+                # handles that safely (no arbitrary code execution).
+                try:
+                    import ast as _ast
+                    _parsed = _ast.literal_eval(raw_headers)
+                    if isinstance(_parsed, dict):
+                        headers = _parsed
+                    else:
+                        continue
+                except Exception:
+                    continue
         elif isinstance(raw_headers, dict):
             headers = raw_headers
         else:
diff --git a/decnet/web/ingester.py b/decnet/web/ingester.py
index 188a833..780cf7f 100644
--- a/decnet/web/ingester.py
+++ b/decnet/web/ingester.py
@@ -106,7 +106,17 @@ async def _extract_bounty(repo: BaseRepository, log_data: dict[str, Any]) -> Non
         })
 
     # 2. HTTP User-Agent fingerprint
-    _headers = _fields.get("headers") if isinstance(_fields.get("headers"), dict) else {}
+    _h_raw = _fields.get("headers")
+    if isinstance(_h_raw, dict):
+        _headers = _h_raw
+    elif isinstance(_h_raw, str):
+        try:
+            _parsed = json.loads(_h_raw)
+            _headers = _parsed if isinstance(_parsed, dict) else {}
+        except (json.JSONDecodeError, ValueError):
+            _headers = {}
+    else:
+        _headers = {}
     _ua = _headers.get("User-Agent") or _headers.get("user-agent")
     if _ua:
         await repo.add_bounty({
diff --git a/templates/http/server.py b/templates/http/server.py
index 076c5ac..cb8d17d 100644
--- a/templates/http/server.py
+++ b/templates/http/server.py
@@ -79,7 +79,7 @@ def log_request():
         method=request.method,
         path=request.path,
         remote_addr=request.remote_addr,
-        headers=dict(request.headers),
+        headers=json.dumps(dict(request.headers)),
         body=request.get_data(as_text=True)[:512],
     )
 
diff --git a/tests/test_profiler_behavioral.py b/tests/test_profiler_behavioral.py
index eb18a1b..ecddd31 100644
--- a/tests/test_profiler_behavioral.py
+++ b/tests/test_profiler_behavioral.py
@@ -287,6 +287,18 @@ class TestDetectToolsFromHeaders:
         result = detect_tools_from_headers(events)
         assert result.count("sqlmap") == 1
 
+    def test_json_string_headers(self):
+        # Post-fix format: headers stored as a JSON string (not a dict).
+        e = _mk(0, event_type="request", service="http",
+                fields={"headers": '{"User-Agent": "Nmap Scripting Engine"}'})
+        assert "nmap" in detect_tools_from_headers([e])
+
+    def test_python_repr_headers_fallback(self):
+        # Legacy format: headers stored as Python repr string (str(dict)).
+        e = _mk(0, event_type="request", service="http",
+                fields={"headers": "{'User-Agent': 'Nmap Scripting Engine'}"})
+        assert "nmap" in detect_tools_from_headers([e])
+
 
 # ─── phase_sequence ────────────────────────────────────────────────────────