feat(FN-3773): fix no-op re-squash in merge finalize instead of refusing me

Fixes the merger to re-squash instead of refusing when a no-op merge verification occurs mid-merge, with regression tests added to prevent recurrence. Also replaces hardcoded color/spacing values in ProjectCard and ProjectOverview CSS with design tokens for theme consistency.

Fusion-Task-Id: FN-3773

packages/engine/src/__tests__/merger-no-op-fix-finalize.test.ts

@@ -0,0 +1,105 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import { mkdtempSync, rmSync, writeFileSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { tmpdir } from "node:os";
+import { execSync } from "node:child_process";
+import { commitOrAmendMergeWithFixes } from "../merger.js";
+import { DEFAULT_SETTINGS } from "@fusion/core";
+
+function git(dir: string, cmd: string): string {
+  return execSync(cmd, { cwd: dir, stdio: "pipe" }).toString().trim();
+}
+
+function initRepo(dir: string): void {
+  git(dir, "git init -b main");
+  git(dir, 'git config user.email "test@example.com"');
+  git(dir, 'git config user.name "Test"');
+  git(dir, "git config commit.gpgsign false");
+  writeFileSync(join(dir, "README.md"), "# repo\n");
+  git(dir, "git add README.md");
+  git(dir, 'git commit -m "chore: initial"');
+}
+
+function stageSquashThenClear(dir: string, branch: string, file: string, content: string): string {
+  git(dir, `git checkout -b ${branch}`);
+  writeFileSync(join(dir, file), content);
+  git(dir, `git add ${file}`);
+  git(dir, `git commit -m "feat: add ${file}"`);
+  git(dir, "git checkout main");
+  const preAttemptSha = git(dir, "git rev-parse HEAD");
+  git(dir, `git merge --squash ${branch}`);
+  // Simulate a no-op in-merge fix path where staged squash content gets cleared.
+  git(dir, "git reset HEAD -- .");
+  return preAttemptSha;
+}
+
+const STUB_SETTINGS = {
+  ...DEFAULT_SETTINGS,
+  commitAuthorEnabled: false,
+};
+
+describe("commitOrAmendMergeWithFixes no-op finalize", () => {
+  let dir: string;
+
+  beforeEach(() => {
+    dir = mkdtempSync(join(tmpdir(), "fn-noop-finalize-"));
+    initRepo(dir);
+  });
+
+  afterEach(() => {
+    rmSync(dir, { recursive: true, force: true });
+  });
+
+  it("re-squashes and commits when fix run is a no-op but branch content exists", async () => {
+    const preAttemptSha = stageSquashThenClear(dir, "feat/noop", "feature-a.ts", "export const a = 1;\n");
+    expect(git(dir, "git diff --cached --name-only")).toBe("");
+    expect(git(dir, "git rev-parse HEAD")).toBe(preAttemptSha);
+    expect(readFileSync(join(dir, "feature-a.ts"), "utf-8")).toBe("export const a = 1;\n");
+
+    const result = await commitOrAmendMergeWithFixes(
+      dir,
+      "FN-3773",
+      "feat/noop",
+      "- feat: add feature-a.ts",
+      false,
+      preAttemptSha,
+      "",
+      undefined,
+      STUB_SETTINGS,
+      undefined,
+      null,
+      null,
+      new Set<string>(),
+    );
+
+    expect(result).toBe(true);
+    const committedFiles = git(dir, "git diff --name-only HEAD~1 HEAD").split("\n").filter(Boolean);
+    expect(committedFiles).toContain("feature-a.ts");
+  });
+
+  it("still refuses real phantom finalize when nothing staged and HEAD belongs to another task", async () => {
+    // Real phantom case: no current-task squash state and HEAD belongs to another task.
+    writeFileSync(join(dir, "outside.txt"), "outside\n");
+    git(dir, "git add outside.txt");
+    git(dir, 'git commit -m "feat: unrelated commit\n\nFusion-Task-Id: FN-OTHER"');
+    const preAttemptSha = git(dir, "git rev-parse HEAD");
+
+    const result = await commitOrAmendMergeWithFixes(
+      dir,
+      "FN-3773",
+      "feat/phantom",
+      "- feat: add feature-b.ts",
+      false,
+      preAttemptSha,
+      "",
+      undefined,
+      STUB_SETTINGS,
+      undefined,
+      null,
+      null,
+      new Set<string>(),
+    );
+
+    expect(result).toBe(false);
+  });
+});