前端进度条性能优化、仿真结束后后处理优化；后端C代码生成流程优化：先识别来源，再按照已知未知量需求排序，最后局部求解

frontend/tests/e2e/free-placement.spec.ts

@@ -0,0 +1,66 @@
+import { expect, test, type Locator } from "@playwright/test";
+import { prepareApp } from "./fixtures";
+
+async function bounds(locator: Locator) {
+  const box = await locator.boundingBox();
+  expect(box).not.toBeNull();
+  return { ...box!, cx: box!.x + box!.width / 2, cy: box!.y + box!.height / 2 };
+}
+
+test("不再提供网格吸附或网格线开关，拖入、微移和粘贴不再对网格取整", async ({ page }) => {
+  await prepareApp(page);
+  await page.goto("/");
+  await expect(page.getByRole("button", { name: /网格吸附|主网格线/ })).toHaveCount(0);
+  await expect(page.locator('pattern[id$="major-grid-lines"]')).toHaveCount(0);
+  await expect(page.locator('pattern[id$="minor-grid-dots"]')).toHaveCount(1);
+  const pane = page.locator(".flow-canvas .react-flow__pane");
+  const canvas = await bounds(pane);
+  const drop = { x: 231, y: 197 };
+  await page.getByRole("button", { name: /通用测试元件/ }).dragTo(pane, { targetPosition: drop });
+  const node = page.locator('.flow-canvas .react-flow__node[data-id="generic_sensor_1"]');
+  const initial = await bounds(node);
+  expect(initial.cx).toBeCloseTo(canvas.x + drop.x, 0);
+  expect(initial.cy).toBeCloseTo(canvas.y + drop.y, 0);
+
+  // 先跨过 React Flow 的拖拽阈值，再移动少于原网格间距的距离。
+  await page.mouse.move(initial.cx, initial.cy);
+  await page.mouse.down();
+  await page.mouse.move(initial.cx, initial.cy + 5);
+  const started = await bounds(node);
+  await page.mouse.move(initial.cx + 7, initial.cy + 16);
+  await page.mouse.up();
+  const moved = await bounds(node);
+  expect(moved.x - started.x).toBeCloseTo(7, 0);
+  expect(moved.y - started.y).toBeCloseTo(11, 0);
+
+  await page.keyboard.press("Control+c");
+  await page.keyboard.press("Control+v");
+  const pointer = { x: canvas.x + 493, y: canvas.y + 371 };
+  await page.mouse.move(pointer.x, pointer.y);
+  const preview = page.locator(".flow-canvas .pending-paste-node");
+  await expect(preview).toBeVisible();
+  const pending = await bounds(preview);
+  expect(pending.cx).toBeCloseTo(pointer.x, 0);
+  expect(pending.cy).toBeCloseTo(pointer.y, 0);
+  await page.mouse.click(pointer.x, pointer.y);
+  await expect(preview).toHaveCount(0);
+  const placed = await bounds(page.locator('.react-flow__node[data-id="generic_sensor_2"]'));
+  expect(placed.cx).toBeCloseTo(pointer.x, 0);
+  expect(placed.cy).toBeCloseTo(pointer.y, 0);
+});
+
+test("忽略旧版网格线开关并保留网格点偏好", async ({ page }) => {
+  await prepareApp(page);
+  await page.addInitScript(() => localStorage.setItem(
+    "system-simulation-flow:canvas-grid-visibility", JSON.stringify({ lines: true, dots: false }),
+  ));
+  await page.goto("/");
+  await expect(page.locator(".flow-canvas .react-flow__background")).toHaveCount(0);
+  await expect(page.getByRole("button", { name: /网格吸附|主网格线/ })).toHaveCount(0);
+  await page.getByRole("button", { name: "显示网格点", exact: true }).click();
+  await expect(page.locator('pattern[id$="minor-grid-dots"]')).toHaveCount(1);
+  await expect(page.locator('pattern[id$="major-grid-lines"]')).toHaveCount(0);
+  await expect.poll(() => page.evaluate(() => JSON.parse(localStorage.getItem(
+    "system-simulation-flow:canvas-grid-visibility",
+  )!))).toEqual({ dots: true });
+});