feat(f7.1): flowchart parser (#22)

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

test/mermaidFlowchartDiff.test.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from "vitest";
+import { parseFlowchart } from "../src/mermaidFlowchartDiff";
+
+describe("parseFlowchart", () => {
+  it("captures the header and node declarations with labels + shapes", () => {
+    const g = parseFlowchart("flowchart LR\n  A[Start] --> B(Middle)\n  B --> C{End}");
+    expect(g.header).toBe("flowchart LR");
+    expect(g.nodes.get("A")).toMatchObject({ id: "A", label: "Start", open: "[", close: "]" });
+    expect(g.nodes.get("B")).toMatchObject({ id: "B", label: "Middle", open: "(", close: ")" });
+    expect(g.nodes.get("C")).toMatchObject({ id: "C", label: "End", open: "{", close: "}" });
+  });
+
+  it("captures edges in declaration order with from/to and index", () => {
+    const g = parseFlowchart("graph TD\n A-->B\n B-->C");
+    expect(g.edges.map((e) => [e.from, e.to, e.index])).toEqual([
+      ["A", "B", 0],
+      ["B", "C", 1],
+    ]);
+  });
+
+  it("records a node referenced only in an edge (no explicit declaration)", () => {
+    const g = parseFlowchart("flowchart LR\n A-->B");
+    expect(g.nodes.has("A")).toBe(true);
+    expect(g.nodes.has("B")).toBe(true);
+    expect(g.nodes.get("A")?.label).toBeUndefined();
+  });
+
+  it("handles a labelled edge `A -->|yes| B`", () => {
+    const g = parseFlowchart("flowchart LR\n A -->|yes| B");
+    expect(g.edges[0]).toMatchObject({ from: "A", to: "B", label: "yes" });
+  });
+
+  it("ignores comments and blank lines", () => {
+    const g = parseFlowchart("flowchart LR\n%% a comment\n\n A-->B");
+    expect(g.edges).toHaveLength(1);
+  });
+});