diff --git a/gateway/hooks.py b/gateway/hooks.py
index f887cf5df04..5ab45119202 100644
--- a/gateway/hooks.py
+++ b/gateway/hooks.py
@@ -21,6 +21,7 @@ Errors in hooks are caught and logged but never block the main pipeline.
 
 import asyncio
 import importlib.util
+import sys
 from typing import Any, Callable, Dict, List, Optional
 
 import yaml
@@ -97,16 +98,28 @@ class HookRegistry:
                     print(f"[hooks] Skipping {hook_name}: no events declared", flush=True)
                     continue
 
-                # Dynamically load the handler module
+                # Dynamically load the handler module.
+                # Register in sys.modules BEFORE exec_module so Pydantic /
+                # dataclasses / typing introspection can resolve forward
+                # references (triggered by `from __future__ import annotations`
+                # in the handler). Without this, a handler that declares a
+                # Pydantic BaseModel for webhook/event payloads fails at first
+                # dispatch with "TypeAdapter ... is not fully defined".
+                module_name = f"hermes_hook_{hook_name}"
                 spec = importlib.util.spec_from_file_location(
-                    f"hermes_hook_{hook_name}", handler_path
+                    module_name, handler_path
                 )
                 if spec is None or spec.loader is None:
                     print(f"[hooks] Skipping {hook_name}: could not load handler.py", flush=True)
                     continue
 
                 module = importlib.util.module_from_spec(spec)
-                spec.loader.exec_module(module)
+                sys.modules[module_name] = module
+                try:
+                    spec.loader.exec_module(module)
+                except Exception:
+                    sys.modules.pop(module_name, None)
+                    raise
 
                 handle_fn = getattr(module, "handle", None)
                 if handle_fn is None:
diff --git a/hermes_cli/web_server.py b/hermes_cli/web_server.py
index 569449f188d..c9f8f6bf1b9 100644
--- a/hermes_cli/web_server.py
+++ b/hermes_cli/web_server.py
@@ -3224,13 +3224,23 @@ def _mount_plugin_api_routes():
             _log.warning("Plugin %s declares api=%s but file not found", plugin["name"], api_file_name)
             continue
         try:
-            spec = importlib.util.spec_from_file_location(
-                f"hermes_dashboard_plugin_{plugin['name']}", api_path,
-            )
+            module_name = f"hermes_dashboard_plugin_{plugin['name']}"
+            spec = importlib.util.spec_from_file_location(module_name, api_path)
             if spec is None or spec.loader is None:
                 continue
             mod = importlib.util.module_from_spec(spec)
-            spec.loader.exec_module(mod)
+            # Register in sys.modules BEFORE exec_module so pydantic/FastAPI
+            # can resolve forward references (e.g. models defined in a file
+            # that uses `from __future__ import annotations`). Without this,
+            # TypeAdapter lazy-build fails at first request with
+            # "is not fully defined" because the module namespace isn't
+            # reachable by name for string-annotation resolution.
+            sys.modules[module_name] = mod
+            try:
+                spec.loader.exec_module(mod)
+            except Exception:
+                sys.modules.pop(module_name, None)
+                raise
             router = getattr(mod, "router", None)
             if router is None:
                 _log.warning("Plugin %s api file has no 'router' attribute", plugin["name"])