chore(types): annotate fifteen signatures mypy could not check

Twelve gain `-> None`, each confirmed by AST to contain no returning
`return` and no `yield` rather than by reading the name and assuming.
The three context-manager exits gain the canonical
type[BaseException]/BaseException/TracebackType argument triple.

Both files taking TracebackType needed the import, and inserting it
before the first import broke ruff's I001 — lint was exit 0 at the
baseline commit, verified by stashing this work and re-running, so that
breakage was mine. Fixed with `ruff check --fix` on the two files, which
placed the import in sorted position.

86 errors -> 75; no-untyped-def 29 -> 14.

Suite: 658 passed. The baseline was 657 passed with one failure in
test_tatlock_tool_call_logging_calculator, which asserts on the content
of a live model's reply. It passing here is nondeterminism, NOT evidence
this commit fixed anything, and it may fail again on the next run.

Co-Authored-By: Claude <noreply@anthropic.com>

src/core/context.py

@@ -18,6 +18,7 @@ Usage:
 """
 
 from contextvars import ContextVar
+from types import TracebackType
 
 
 def get_default_user() -> str:
@@ -142,7 +143,12 @@ class RequestContext:
         self._conv_token = current_conversation.set(self.conversation_id)
         return self
 
-    async def __aexit__(self, exc_type, exc_val, exc_tb) -> None:
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
         """Reset context variables on exit."""
         if self._user_token is not None:
             current_user.reset(self._user_token)
@@ -155,7 +161,12 @@ class RequestContext:
         self._conv_token = current_conversation.set(self.conversation_id)
         return self
 
-    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
+    def __exit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
         """Sync context manager exit."""
         if self._user_token is not None:
             current_user.reset(self._user_token)