feat: introduce local-first SVG workbench

tests/commands/history.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, it, vi } from "vitest";
+import { CommandHistory, createTransaction } from "../../src/commands/history";
+
+describe("source transaction history", () => {
+  it("undoes and redoes exact source without normalization", () => {
+    const history = new CommandHistory();
+    const transaction = createTransaction({
+      label: "Set fill",
+      baseRevision: 1,
+      sourceBefore: "<svg><path/></svg>\r\n",
+      sourceAfter: '<svg><path fill="red"/></svg>\r\n',
+    });
+    history.commit(transaction);
+    expect(history.undo(transaction.sourceAfter)?.sourceBefore).toBe(
+      transaction.sourceBefore,
+    );
+    expect(history.redo(transaction.sourceBefore)?.sourceAfter).toBe(
+      transaction.sourceAfter,
+    );
+  });
+
+  it("coalesces rapid source-editor transactions with a shared merge key", () => {
+    vi.spyOn(Date, "now").mockReturnValueOnce(100).mockReturnValueOnce(200);
+    const history = new CommandHistory();
+    history.commit(
+      createTransaction({
+        label: "Type",
+        baseRevision: 0,
+        sourceBefore: "a",
+        sourceAfter: "ab",
+        mergeKey: "typing",
+      }),
+    );
+    history.commit(
+      createTransaction({
+        label: "Type",
+        baseRevision: 1,
+        sourceBefore: "ab",
+        sourceAfter: "abc",
+        mergeKey: "typing",
+      }),
+    );
+    expect(history.snapshot.past).toHaveLength(1);
+    expect(history.snapshot.past[0]).toMatchObject({
+      sourceBefore: "a",
+      sourceAfter: "abc",
+    });
+  });
+
+  it("rejects stale undo and bounds history", () => {
+    const history = new CommandHistory(2, 10_000);
+    history.commit(
+      createTransaction({
+        label: "one",
+        baseRevision: 0,
+        sourceBefore: "a",
+        sourceAfter: "b",
+      }),
+    );
+    expect(() => history.undo("not-b")).toThrow(/stale/u);
+    history.commit(
+      createTransaction({
+        label: "two",
+        baseRevision: 1,
+        sourceBefore: "b",
+        sourceAfter: "c",
+      }),
+    );
+    history.commit(
+      createTransaction({
+        label: "three",
+        baseRevision: 2,
+        sourceBefore: "c",
+        sourceAfter: "d",
+      }),
+    );
+    expect(history.snapshot.past).toHaveLength(2);
+  });
+});