feat(f7.1): flowchart node/edge diff + styling emission (#22)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

test/mermaidFlowchartDiff.test.ts

@@ -35,3 +35,50 @@ describe("parseFlowchart", () => {
     expect(g.edges).toHaveLength(1);
   });
 });
+
+import { diffFlowchart } from "../src/mermaidFlowchartDiff";
+
+describe("diffFlowchart", () => {
+  it("colors an added node with the cwAdded class", () => {
+    const before = "flowchart LR\n A-->B";
+    const current = "flowchart LR\n A-->B\n B-->C";
+    const out = diffFlowchart(before, current);
+    expect(out).toContain("classDef cwAdded");
+    expect(out).toMatch(/class\s+C\s+cwAdded/);
+  });
+
+  it("colors a changed node (same id, new label) with cwChanged", () => {
+    const before = "flowchart LR\n A[Old]-->B";
+    const current = "flowchart LR\n A[New]-->B";
+    const out = diffFlowchart(before, current);
+    expect(out).toMatch(/class\s+A\s+cwChanged/);
+  });
+
+  it("styles an added edge via linkStyle on its current index", () => {
+    const before = "flowchart LR\n A-->B";
+    const current = "flowchart LR\n A-->B\n A-->C";
+    const out = diffFlowchart(before, current);
+    // edge index 1 (A-->C) is the added one
+    expect(out).toMatch(/linkStyle\s+1\s+stroke:#2ea043/);
+  });
+
+  it("ghosts a removed node in place with cwRemoved (re-injected decl)", () => {
+    const before = "flowchart LR\n A-->B\n B-->C[Gone]";
+    const current = "flowchart LR\n A-->B";
+    const out = diffFlowchart(before, current);
+    expect(out).toContain("C[Gone]"); // re-injected
+    expect(out).toMatch(/class\s+C\s+cwRemoved/);
+  });
+
+  it("is deterministic (same inputs → identical output)", () => {
+    const before = "flowchart LR\n A-->B";
+    const current = "flowchart LR\n A-->B\n B-->C\n A-->D";
+    expect(diffFlowchart(before, current)).toBe(diffFlowchart(before, current));
+  });
+
+  it("preserves the original current source as the prefix", () => {
+    const current = "flowchart LR\n A-->B\n B-->C";
+    const out = diffFlowchart("flowchart LR\n A-->B", current);
+    expect(out.startsWith(current)).toBe(true);
+  });
+});