diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 62280d1..dfb70f3 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -79,6 +79,12 @@ repos:
     - pydantic-settings>=2.0
     - httpx>=0.27
     - typing-extensions>=4.0
+        # Optional-extra deps required so the now-strictly-checked modules
+        # under ``locus.a2a``, ``locus.integrations``, ``locus.server`` etc.
+        # resolve their third-party imports.
+    - fastapi>=0.110
+    - fastmcp>=3.2.0
+    - mcp>=1.0
     pass_filenames: false
     entry: mypy src/locus
 
diff --git a/pyproject.toml b/pyproject.toml
index bb5e24a..87e30ae 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -525,16 +525,11 @@ ignore_missing_imports = true
 module = [
     "locus.rag.*",
     "locus.memory.*",
-    "locus.integrations.*",
-    "locus.streaming.*",
     "locus.loop.*",
-    "locus.playbooks.*",
     "locus.server.*",
     "locus.multiagent.graph",
     "locus.hooks.builtin.*",
     "locus.reasoning.*",
-    "locus.skills.*",
-    "locus.a2a.*",
 ]
 ignore_errors = true
 
diff --git a/src/locus/a2a/protocol.py b/src/locus/a2a/protocol.py
index 2a7fb4c..aac8495 100644
--- a/src/locus/a2a/protocol.py
+++ b/src/locus/a2a/protocol.py
@@ -30,6 +30,7 @@
 import logging
 import os
 import uuid
+from collections.abc import AsyncIterator
 from typing import Any
 
 from pydantic import BaseModel, Field
@@ -238,7 +239,7 @@ async def stream(
             user_msgs = [m for m in request.messages if m.role == "user"]
             prompt = user_msgs[-1].content if user_msgs else ""
 
-            async def event_generator():
+            async def event_generator() -> AsyncIterator[str]:
                 try:
                     async for event in agent.run(prompt):
                         if isinstance(event, ThinkEvent):
diff --git a/src/locus/integrations/fastmcp.py b/src/locus/integrations/fastmcp.py
index e4b3d09..f0442b1 100644
--- a/src/locus/integrations/fastmcp.py
+++ b/src/locus/integrations/fastmcp.py
@@ -18,7 +18,7 @@
 import json
 import re
 from collections.abc import Callable
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Literal
 
 from pydantic import BaseModel, ConfigDict, Field, create_model
 
@@ -68,7 +68,10 @@ def _json_schema_type_to_python(prop: dict[str, Any]) -> type[Any]:
         "boolean": bool,
     }
 
-    return mapping.get(schema_type, Any)
+    # ``Any`` is a typing-special-form, not a runtime type, so mypy can't
+    # accept it as the dict default. Pydantic accepts it as a field type
+    # at runtime, so we tag the line.
+    return mapping.get(schema_type, Any)  # type: ignore[arg-type]
 
 
 def build_args_model(tool_name: str, schema: dict[str, Any] | None) -> type[BaseModel] | None:
@@ -315,7 +318,7 @@ def _create_mcp(self) -> FastMCP:
         async def run_agent(prompt: str) -> str:
             """Run the Locus agent with a prompt and return the response."""
             result = agent.run_sync(prompt)
-            return result.message
+            return str(result.message)
 
         # Register a streaming version
         @mcp.tool()
@@ -327,17 +330,17 @@ async def run_agent_stream(prompt: str) -> str:
             # Return the final message from the last event
             for event in reversed(events):
                 if hasattr(event, "final_message") and event.final_message:
-                    return event.final_message
+                    return str(event.final_message)
             return "Agent completed without response"
 
         return mcp
 
-    def run(self, transport: str = "stdio") -> None:
+    def run(self, transport: Literal["stdio", "http", "sse", "streamable-http"] = "stdio") -> None:
         """
         Run the MCP server.
 
         Args:
-            transport: Transport type ("stdio" or "sse")
+            transport: Transport type ("stdio", "http", "sse", or "streamable-http").
         """
         if self._mcp is None:
             self._mcp = self._create_mcp()
@@ -491,6 +494,9 @@ async def connect(self) -> None:
 
     async def _connect_http(self) -> None:
         """Connect via HTTP/SSE transport."""
+        if self.base_url is None:
+            msg = "_connect_http called without base_url"
+            raise RuntimeError(msg)
         try:
             from mcp.client.session import ClientSession
             from mcp.client.streamable_http import streamablehttp_client
@@ -517,7 +523,9 @@ class BearerAuth(httpx.Auth):
                 def __init__(self, token: str):
                     self.token = token
 
-                def auth_flow(self, request):
+                def auth_flow(  # type: ignore[no-untyped-def]
+                    self, request
+                ):  # httpx.Auth.auth_flow signature varies across SDK versions
                     request.headers["Authorization"] = f"Bearer {self.token}"
                     yield request
 
@@ -647,12 +655,17 @@ async def close(self) -> None:
                 pass
             self._client_context = None
 
-    async def __aenter__(self):
+    async def __aenter__(self) -> MCPClient:
         """Async context manager entry."""
         await self.connect()
         return self
 
-    async def __aexit__(self, exc_type, exc_val, exc_tb):
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: Any,
+    ) -> None:
         """Async context manager exit."""
         await self.close()
 
diff --git a/src/locus/playbooks/hook.py b/src/locus/playbooks/hook.py
index 7b19182..a9b2d8a 100644
--- a/src/locus/playbooks/hook.py
+++ b/src/locus/playbooks/hook.py
@@ -100,7 +100,12 @@ def enforcer(self) -> PlaybookEnforcer:
 
     async def on_before_tool_call(self, event: BeforeToolCallEvent) -> None:
         """Validate the call against the current step; cancel on violation."""
-        result = self._enforcer.validate_tool_call(event.tool_name)
+        # ``ProtectedEvent`` (the base class for hook events) sets fields
+        # via ``self._init(name, value)`` rather than class-level annotations,
+        # so mypy can't see ``.tool_name`` / ``.error`` statically. They
+        # exist at runtime; the ignore is the standard pattern for this
+        # protocol.
+        result = self._enforcer.validate_tool_call(event.tool_name)  # type: ignore[attr-defined]
         if result.allowed:
             return
         # Build a useful cancel message that the agent loop will turn into
@@ -120,13 +125,16 @@ async def on_after_tool_call(self, event: AfterToolCallEvent) -> None:
         before-hook cancelled the call, so anything reaching this method
         actually executed.
         """
-        if event.error:
+        # ``ProtectedEvent`` sets ``.error`` / ``.tool_name`` via
+        # ``self._init(...)`` not class-level fields — see note in
+        # ``on_before_tool_call``.
+        if event.error:  # type: ignore[attr-defined]
             # Failed calls don't advance the step (the model will likely
             # retry); they're still recorded for the violation log.
-            self._enforcer.record_tool_call(event.tool_name)
+            self._enforcer.record_tool_call(event.tool_name)  # type: ignore[attr-defined]
             return
 
-        self._enforcer.record_tool_call(event.tool_name)
+        self._enforcer.record_tool_call(event.tool_name)  # type: ignore[attr-defined]
 
         step = self._enforcer.current_step
         if step is None:
diff --git a/src/locus/playbooks/loader.py b/src/locus/playbooks/loader.py
index 0158547..ca24d9b 100644
--- a/src/locus/playbooks/loader.py
+++ b/src/locus/playbooks/loader.py
@@ -126,7 +126,7 @@ def load_yaml_string(self, yaml_string: str) -> Playbook:
             PlaybookLoadError: If YAML is invalid or playbook validation fails
         """
         try:
-            import yaml
+            import yaml  # type: ignore[import-untyped]  # PyYAML ships no inline types
         except ImportError as e:
             raise PlaybookLoadError(
                 "PyYAML is required for YAML support. Install with: pip install pyyaml"
diff --git a/src/locus/skills/models.py b/src/locus/skills/models.py
index 8369b0f..0ec536d 100644
--- a/src/locus/skills/models.py
+++ b/src/locus/skills/models.py
@@ -29,7 +29,7 @@
 from pathlib import Path
 from typing import Any
 
-import yaml
+import yaml  # type: ignore[import-untyped]  # PyYAML ships no inline types
 
 
 # AgentSkills.io name validation: kebab-case, 1-64 chars, no consecutive hyphens
diff --git a/src/locus/streaming/sse.py b/src/locus/streaming/sse.py
index 4b35003..2113122 100644
--- a/src/locus/streaming/sse.py
+++ b/src/locus/streaming/sse.py
@@ -184,7 +184,8 @@ def _serialize_event(self, event: LocusEvent) -> dict[str, Any]:
             Dictionary representation of the event
         """
         if self.custom_serializer:
-            return self.custom_serializer(event)
+            # User-supplied callable; mypy can't narrow its return.
+            return self.custom_serializer(event)  # type: ignore[no-any-return]
 
         # Use Pydantic's model_dump
         data = event.model_dump()