diff --git a/.github/actions/setup/action.yml b/.github/actions/setup/action.yml
index 5827afa2e..b49ad9856 100644
--- a/.github/actions/setup/action.yml
+++ b/.github/actions/setup/action.yml
@@ -35,17 +35,21 @@ runs:
         BROWSERS: ${{ inputs.browsers }}
       run: |
         echo "version=$(pnpm exec playwright --version | awk '{ print $NF }')" >>"$GITHUB_OUTPUT"
+        echo "distro=$(. /etc/os-release && echo "$ID$VERSION_ID")" >>"$GITHUB_OUTPUT"
         echo "slug=${BROWSERS// /-}" >>"$GITHUB_OUTPUT"
 
-    # The browser binaries are the slow half of the install and they only ever
-    # change with the Playwright version, so a hit leaves just the apt step.
+    # The browser binaries are the slow half of the install. Playwright ships a
+    # separate build per distro release (WebKit links against that release's
+    # ICU), so the key carries the distro too: when ubuntu-latest moved to
+    # 26.04 a key without it restored the 24.04 WebKit, which cannot start
+    # there (libicudata.so.74 missing).
     - name: Restore the Playwright browser cache
       if: inputs.browsers != ''
       id: browser-cache
       uses: actions/cache@v6
       with:
         path: ~/.cache/ms-playwright
-        key: playwright-${{ runner.os }}-${{ steps.playwright.outputs.version }}-${{ steps.playwright.outputs.slug }}
+        key: playwright-${{ runner.os }}-${{ steps.playwright.outputs.distro }}-${{ runner.arch }}-${{ steps.playwright.outputs.version }}-${{ steps.playwright.outputs.slug }}
 
     - name: Install Playwright browsers
       if: inputs.browsers != ''
diff --git a/CLAUDE.md b/CLAUDE.md
index 707ed37cb..d20494b0c 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -434,7 +434,7 @@ apt-get，而 hosted runner 上的 apt 有过**拉完 release 索引后彻底停
 每次挂在不同的 job（三个 e2e job 跑的是同一步，谁中枪是随机的），每次都要人工
 重跑。apt 自身没有总时长上限，所以 `.github/scripts/install-playwright.sh` 给
 每次尝试套 `timeout` 并重试，重试前清掉被杀的 apt 留下的锁；浏览器二进制
-按 Playwright 版本号进 `actions/cache`，命中时只跑 `install-deps`。
+按"发行版 + 架构 + Playwright 版本号"进 `actions/cache`（Playwright 每个 Ubuntu 版本一套构建，2026-11-03 漏了发行版，26.04 的机器取回 24.04 的 WebKit 起不来），命中时只跑 `install-deps`。
 
 **缓存命中时直接不跑 apt**（2026-08-19 起）。读健康 run 的日志才看清 `install-deps`
 到底在干什么：Chromium 要的库（libnss3 / libgbm1 / libasound2t64 / libcairo2 …）
diff --git a/docs/explorations/2026-11-03-playwright-cache-distro.md b/docs/explorations/2026-11-03-playwright-cache-distro.md
new file mode 100644
index 000000000..d3aa6fc65
--- /dev/null
+++ b/docs/explorations/2026-11-03-playwright-cache-distro.md
@@ -0,0 +1,42 @@
+# 夜间跨浏览器全红：浏览器缓存没带发行版
+
+2026-11-03 的 Nightly corpus（run 41561076181）cross-browser 红：WebKit 三个分片 + serial
+全部 1ms 失败，Firefox 分片 2 有 4 条失败。
+
+## 根因（WebKit）
+
+日志里每条 WebKit 用例都是同一句：
+
+```
+MiniBrowser: error while loading shared libraries: libicudata.so.74: cannot open shared object file
+```
+
+- `ubuntu-latest` 从这周起指向 **ubuntu-26.04**（10-30 那次跨浏览器还是 24.04，全绿；
+  中间两晚 gate 判定没有新提交、跨浏览器没跑，所以这是 26.04 上第一次跑）。
+- Playwright 1.64 对每个 Ubuntu 版本发一套独立构建（`coreBundle.js` 里有
+  `ubuntu24.04-x64` / `ubuntu26.04-x64` 两套下载项），WebKit 链接的是那个版本自己的 ICU。
+- `.github/actions/setup` 的缓存 key 是 `playwright-Linux-1.64.0-webkit`——没有发行版。
+  26.04 的机器命中了 24.04 时存进去的缓存，拿到的是 24.04 的 WebKit，而 26.04 上没有 ICU 74。
+- 命中缓存时安装脚本直接 `exit 0`（不跑 apt，见 CLAUDE.md CI 一节），所以也没有任何一步会
+  发现版本对不上。
+
+## 改动
+
+- 缓存 key 加上 `/etc/os-release` 的 `$ID$VERSION_ID` 与 `runner.arch`：
+  `playwright-Linux-ubuntu26.04-X64-1.64.0-webkit`。换镜像就是冷缓存，走完整安装
+  （含 `install-deps`），之后再命中的才是同一发行版的构建。
+- `test/unit/workflow-contract.test.ts` 钉住 key 里的发行版段。反向验证：只撤
+  action.yml 的改动，这条用例变红；恢复后 68/68 绿。
+
+## Firefox 那 4 条
+
+`agent-interface-affordances.spec.ts:65`：`Tab` 再 `Shift+Tab` 之后
+"Import structured result" 按钮没拿到焦点（`inactive`），4 个视口/主题组合全挂、重试也挂。
+Firefox 能启动，但跑的同样是 24.04 的构建，跑在 26.04 上。是不是同一个原因，本地（macOS）
+复现不了；以修复后在分支上手动触发一次 nightly（`skip_corpus`）的结果为准，若仍红再单独查。
+
+## 还没验证的一点
+
+缓存命中时不跑 apt，前提是 runner 镜像本来就带齐浏览器要的库——这是 24.04 上读日志得出的
+结论，26.04 上没验证过。验证方法：在分支上手动跑两次 nightly（第一次冷缓存，第二次命中），
+第二次 WebKit 也能起来才算闭环。
diff --git a/test/unit/workflow-contract.test.ts b/test/unit/workflow-contract.test.ts
index e6bd59b52..aae205647 100644
--- a/test/unit/workflow-contract.test.ts
+++ b/test/unit/workflow-contract.test.ts
@@ -105,10 +105,15 @@ describe('the shared setup action', () => {
     expect(action).not.toMatch(/run: pnpm exec playwright install/);
   });
 
-  it('caches the browsers against the Playwright version, not the lockfile', () => {
+  it('caches the browsers against the distro and Playwright version, not the lockfile', () => {
     // Keying on the lockfile would evict the cache on every dependency bump
-    // and re-download the browsers for no reason.
-    expect(action).toMatch(/key: playwright-\$\{\{ runner\.os \}\}-\$\{\{ steps\.playwright\.outputs\.version \}\}/);
+    // and re-download the browsers for no reason. The distro is part of the
+    // key because Playwright builds per release: without it the 24.04 WebKit
+    // was restored onto the 26.04 runner and could not start.
+    expect(action).toMatch(/distro=\$\(\. \/etc\/os-release && echo "\$ID\$VERSION_ID"\)/);
+    expect(action).toMatch(
+      /key: playwright-\$\{\{ runner\.os \}\}-\$\{\{ steps\.playwright\.outputs\.distro \}\}-\$\{\{ runner\.arch \}\}-\$\{\{ steps\.playwright\.outputs\.version \}\}/,
+    );
   });
 });