test: narrow db._conn before raw SQL so ty stops flagging None-union access

The new compression-tip tests poke started_at/ended_at directly via
db._conn to force deterministic lineage ordering. _conn is typed
Optional[Connection], so ty flagged .execute/.commit as unresolved on
None. Bind a local and assert it's non-None first to narrow the union.

tests/hermes_state/test_resolve_resume_session_id.py

@@ -100,9 +100,11 @@ def test_follows_compression_tip_when_parent_retains_messages(db):
     db.append_message("cont", role="assistant", content="post-compression reply")
     # Force deterministic ordering so the continuation's started_at is clearly
     # at/after the parent's ended_at (the get_compression_tip discriminator).
-    db._conn.execute("UPDATE sessions SET started_at = ?, ended_at = ? WHERE id = 'root'", (base, base + 50))
-    db._conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'cont'", (base + 100,))
-    db._conn.commit()
+    conn = db._conn
+    assert conn is not None
+    conn.execute("UPDATE sessions SET started_at = ?, ended_at = ? WHERE id = 'root'", (base, base + 50))
+    conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'cont'", (base + 100,))
+    conn.commit()
 
     assert db.resolve_resume_session_id("root") == "cont"
 
@@ -116,9 +118,11 @@ def test_compression_tip_not_confused_with_delegation_child(db):
     db.append_message("conv", role="user", content="parent turn")
     db.create_session("subagent", source="cli", parent_session_id="conv")
     db.append_message("subagent", role="assistant", content="delegated work")
-    db._conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'conv'", (base,))
-    db._conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'subagent'", (base + 100,))
-    db._conn.commit()
+    conn = db._conn
+    assert conn is not None
+    conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'conv'", (base,))
+    conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'subagent'", (base + 100,))
+    conn.commit()
 
     assert db.resolve_resume_session_id("conv") == "conv"
 

tests/test_tui_gateway_server.py

@@ -973,12 +973,14 @@ def test_session_resume_follows_compression_tip(monkeypatch, tmp_path):
     db.end_session("parent_root", "compression")
     db.create_session("cont_tip", source="tui", parent_session_id="parent_root")
     db.append_message("cont_tip", role="assistant", content="post-compression reply")
-    db._conn.execute(
+    conn = db._conn
+    assert conn is not None
+    conn.execute(
         "UPDATE sessions SET started_at = ?, ended_at = ? WHERE id = 'parent_root'",
         (base, base + 50),
     )
-    db._conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'cont_tip'", (base + 100,))
-    db._conn.commit()
+    conn.execute("UPDATE sessions SET started_at = ? WHERE id = 'cont_tip'", (base + 100,))
+    conn.commit()
 
     captured = {}