test: improve coverage for snippets and stateMapper

Add comprehensive test coverage to prevent regressions:

**Snippets Store:**
- Test filteredSnippets derived store with and without category filter
- Cover all branches of the filter logic

**State Mapper:**
- Test unknown tool handling (defaults to typing)
- Test thinking content blocks in assistant messages
- Test empty content arrays
- Test all stream_event delta types (thinking_delta, text_delta)
- Test all content_block_start types (thinking, text, tool_use)
- Test unrecognized stream event types
- Test unknown result subtypes
- Test unknown message types
- Test extractTextFromMessage edge cases (null result, no delta text)

These additions bring test count from 335 to 351 and significantly improve
branch coverage for these critical utility functions.

src/lib/stores/snippets.test.ts

@@ -285,6 +285,73 @@ describe("snippetsStore", () => {
       expect(get(snippetsStore.selectedCategory)).toBeNull();
     });
   });
+
+  describe("filteredSnippets", () => {
+    it("returns all snippets when no category selected", async () => {
+      const mockSnippets: Snippet[] = [
+        {
+          id: "snippet-1",
+          name: "Git Status",
+          content: "git status",
+          category: "Git",
+          is_default: false,
+          created_at: "2024-01-01T00:00:00Z",
+          updated_at: "2024-01-01T00:00:00Z",
+        },
+        {
+          id: "snippet-2",
+          name: "Docker PS",
+          content: "docker ps",
+          category: "Docker",
+          is_default: false,
+          created_at: "2024-01-01T00:00:00Z",
+          updated_at: "2024-01-01T00:00:00Z",
+        },
+      ];
+
+      setMockInvokeResult("list_snippets", mockSnippets);
+      setMockInvokeResult("get_snippet_categories", ["Git", "Docker"]);
+
+      await snippetsStore.loadSnippets();
+      snippetsStore.setSelectedCategory(null);
+
+      const filtered = get(snippetsStore.filteredSnippets);
+      expect(filtered).toHaveLength(2);
+    });
+
+    it("filters snippets by selected category", async () => {
+      const mockSnippets: Snippet[] = [
+        {
+          id: "snippet-1",
+          name: "Git Status",
+          content: "git status",
+          category: "Git",
+          is_default: false,
+          created_at: "2024-01-01T00:00:00Z",
+          updated_at: "2024-01-01T00:00:00Z",
+        },
+        {
+          id: "snippet-2",
+          name: "Docker PS",
+          content: "docker ps",
+          category: "Docker",
+          is_default: false,
+          created_at: "2024-01-01T00:00:00Z",
+          updated_at: "2024-01-01T00:00:00Z",
+        },
+      ];
+
+      setMockInvokeResult("list_snippets", mockSnippets);
+      setMockInvokeResult("get_snippet_categories", ["Git", "Docker"]);
+
+      await snippetsStore.loadSnippets();
+      snippetsStore.setSelectedCategory("Git");
+
+      const filtered = get(snippetsStore.filteredSnippets);
+      expect(filtered).toHaveLength(1);
+      expect(filtered[0].category).toBe("Git");
+    });
+  });
 });
 
 describe("snippet ID generation", () => {

src/lib/utils/stateMapper.test.ts

@@ -135,6 +135,151 @@ describe("stateMapper", () => {
       };
       expect(mapMessageToState(message)).toBeNull();
     });
+
+    it("returns typing for unknown tool", () => {
+      const message: ClaudeStreamMessage = {
+        type: "assistant",
+        message: {
+          content: [
+            {
+              type: "tool_use",
+              id: "tool-1",
+              name: "SomeUnknownTool",
+              input: {},
+            },
+          ],
+          model: "claude-3",
+          stop_reason: "tool_use",
+        },
+      };
+      expect(mapMessageToState(message)).toBe("typing");
+    });
+
+    it("returns thinking for thinking content block", () => {
+      const message: ClaudeStreamMessage = {
+        type: "assistant",
+        message: {
+          content: [{ type: "thinking", thinking: "Analyzing the problem..." }],
+          model: "claude-3",
+          stop_reason: "end_turn",
+        },
+      };
+      expect(mapMessageToState(message)).toBe("thinking");
+    });
+
+    it("returns null for assistant message with no recognizable content", () => {
+      const message: ClaudeStreamMessage = {
+        type: "assistant",
+        message: {
+          content: [],
+          model: "claude-3",
+          stop_reason: "end_turn",
+        },
+      };
+      expect(mapMessageToState(message)).toBeNull();
+    });
+
+    it("returns thinking for thinking_delta stream event", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_delta",
+          index: 0,
+          delta: {
+            type: "thinking_delta",
+            thinking: "Thinking...",
+          },
+        },
+      };
+      expect(mapMessageToState(message)).toBe("thinking");
+    });
+
+    it("returns typing for text_delta stream event", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_delta",
+          index: 0,
+          delta: {
+            type: "text_delta",
+            text: "Hello",
+          },
+        },
+      };
+      expect(mapMessageToState(message)).toBe("typing");
+    });
+
+    it("returns thinking for thinking content_block_start", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_start",
+          index: 0,
+          content_block: {
+            type: "thinking",
+            thinking: "",
+          },
+        },
+      };
+      expect(mapMessageToState(message)).toBe("thinking");
+    });
+
+    it("returns typing for text content_block_start", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_start",
+          index: 0,
+          content_block: {
+            type: "text",
+            text: "",
+          },
+        },
+      };
+      expect(mapMessageToState(message)).toBe("typing");
+    });
+
+    it("returns correct state for tool_use content_block_start", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_start",
+          index: 0,
+          content_block: {
+            type: "tool_use",
+            id: "tool-1",
+            name: "Read",
+            input: {},
+          },
+        },
+      };
+      expect(mapMessageToState(message)).toBe("searching");
+    });
+
+    it("returns null for stream_event with unrecognized type", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "message_start",
+        },
+      };
+      expect(mapMessageToState(message)).toBeNull();
+    });
+
+    it("returns null for result with unknown subtype", () => {
+      const message: ClaudeStreamMessage = {
+        type: "result",
+        subtype: "unknown_type",
+      };
+      expect(mapMessageToState(message)).toBeNull();
+    });
+
+    it("returns null for unknown message type", () => {
+      const message = {
+        type: "unknown_type",
+      } as unknown as ClaudeStreamMessage;
+      expect(mapMessageToState(message)).toBeNull();
+    });
   });
 
   describe("extractTextFromMessage", () => {
@@ -192,6 +337,36 @@ describe("stateMapper", () => {
       };
       expect(extractTextFromMessage(message)).toBe("Completed successfully");
     });
+
+    it("returns null for result without result field", () => {
+      const message: ClaudeStreamMessage = {
+        type: "result",
+        subtype: "success",
+      };
+      expect(extractTextFromMessage(message)).toBeNull();
+    });
+
+    it("returns null for stream_event without delta text", () => {
+      const message: ClaudeStreamMessage = {
+        type: "stream_event",
+        event: {
+          type: "content_block_start",
+          index: 0,
+          content_block: {
+            type: "text",
+            text: "",
+          },
+        },
+      };
+      expect(extractTextFromMessage(message)).toBeNull();
+    });
+
+    it("returns null for unknown message type", () => {
+      const message = {
+        type: "unknown",
+      } as unknown as ClaudeStreamMessage;
+      expect(extractTextFromMessage(message)).toBeNull();
+    });
   });
 
   describe("extractToolInfo", () => {