test: reorganize test structure and add missing unit tests

Reorganize flat tests/ directory to mirror source code structure
(tools/, gateway/, hermes_cli/, integration/). Add 11 new test files
covering previously untested modules: registry, patch_parser,
fuzzy_match, todo_tool, approval, file_tools, gateway session/config/
delivery, and hermes_cli config/models. Total: 147 unit tests passing,
9 integration tests gated behind pytest marker.

tests/gateway/test_session.py

@@ -0,0 +1,88 @@
+"""Tests for gateway session management."""
+
+from gateway.config import Platform, HomeChannel, GatewayConfig, PlatformConfig
+from gateway.session import (
+    SessionSource,
+    build_session_context,
+    build_session_context_prompt,
+)
+
+
+class TestSessionSourceRoundtrip:
+    def test_to_dict_from_dict(self):
+        source = SessionSource(
+            platform=Platform.TELEGRAM,
+            chat_id="12345",
+            chat_name="My Group",
+            chat_type="group",
+            user_id="99",
+            user_name="alice",
+            thread_id="t1",
+        )
+        d = source.to_dict()
+        restored = SessionSource.from_dict(d)
+
+        assert restored.platform == Platform.TELEGRAM
+        assert restored.chat_id == "12345"
+        assert restored.chat_name == "My Group"
+        assert restored.chat_type == "group"
+        assert restored.user_id == "99"
+        assert restored.user_name == "alice"
+        assert restored.thread_id == "t1"
+
+    def test_minimal_roundtrip(self):
+        source = SessionSource(platform=Platform.LOCAL, chat_id="cli")
+        d = source.to_dict()
+        restored = SessionSource.from_dict(d)
+        assert restored.platform == Platform.LOCAL
+        assert restored.chat_id == "cli"
+
+
+class TestLocalCliSource:
+    def test_local_cli(self):
+        source = SessionSource.local_cli()
+        assert source.platform == Platform.LOCAL
+        assert source.chat_id == "cli"
+        assert source.chat_type == "dm"
+
+    def test_description_local(self):
+        source = SessionSource.local_cli()
+        assert source.description == "CLI terminal"
+
+
+class TestBuildSessionContextPrompt:
+    def test_contains_platform_info(self):
+        config = GatewayConfig(
+            platforms={
+                Platform.TELEGRAM: PlatformConfig(
+                    enabled=True,
+                    token="fake-token",
+                    home_channel=HomeChannel(
+                        platform=Platform.TELEGRAM,
+                        chat_id="111",
+                        name="Home Chat",
+                    ),
+                ),
+            },
+        )
+        source = SessionSource(
+            platform=Platform.TELEGRAM,
+            chat_id="111",
+            chat_name="Home Chat",
+            chat_type="dm",
+        )
+        ctx = build_session_context(source, config)
+        prompt = build_session_context_prompt(ctx)
+
+        assert "Telegram" in prompt
+        assert "Home Chat" in prompt
+        assert "Session Context" in prompt
+
+    def test_local_source_prompt(self):
+        config = GatewayConfig()
+        source = SessionSource.local_cli()
+        ctx = build_session_context(source, config)
+        prompt = build_session_context_prompt(ctx)
+
+        assert "Local" in prompt
+        assert "machine running this agent" in prompt