docs: preserve application focus during Emacs capture

AGENTS.md

@@ -8,6 +8,8 @@
 
 - GUI 与性能自动化先查 `scripts/README.md`、`scripts/emacs-gui-verifier.el`
   及既有 Makefile 入口；公共机制归 `scripts/`，具体业务场景归示例仓库。
+- 现有 Emacs 的截图与录像默认保留用户当前应用焦点，使用已登记的窗口捕获
+  入口；后台视觉证据须检查内容更新，后台耗时与前台输入到显示延迟分别报告。
 - 连续 resize 使用 `scripts/benchmark-ebox-resize.el` 的
   `ebox-resize-benchmark-start`，适用于现有 ETAF 或独立 Ebox buffer。
   按 README 选择范围、轮数和新证据文件；先验证前台与已加载版本，保留全部样本，

scripts/README.md

@@ -4,8 +4,9 @@ For an already running Emacs, use its existing server through `emacsclient`.
 Load the checkout and call the example entry point in an explicit buffer, show
 that buffer in the existing graphical frame, and capture only that owned
 window. Preserve the user's font and chrome. Do not start another daemon or
-frame for this workflow. The `emacsclient-render-capture` skill supplies the
+frame for this workflow. Preserve application focus so the user can keep working
-foreground and before/after target guards.
+in other apps. The `emacsclient-render-capture` skill supplies buffer selection
+without activation and before/after target guards.
 
 This directory also owns reusable verification mechanisms; application
 scenarios live in their respective example repositories:
@@ -21,12 +22,14 @@ scenarios live in their respective example repositories:
   generation, and exact cleanup.
 - `record-emacs-window.swift` uses macOS 15 ScreenCaptureKit to record only the
   frame owned by the supplied Emacs PID. It follows replacement window IDs and
-  rejects changed pixel mappings. Its canvas is fixed at recording start:
+  rejects changed pixel mappings. Its desktop-independent window filter works
+  without activating Emacs. Its canvas is fixed at recording start:
   when the scenario includes resize, prepare the largest tested frame before
   starting the recorder. Smaller windows retain native pixels with padding;
   a window larger than the original canvas invalidates the recording.
 - `capture-emacs-window.sh` supplies window-only checkpoint screenshots and
-  rejects missing, ambiguous, or changing frame identities. The runner compiles
+  rejects missing, ambiguous, or changing frame identities without activating
+  Emacs. The runner compiles
   the video helper using the system Swift compiler; no package install is needed.
 
 Concrete repositories provide adapter files that construct a Scenario and an
@@ -52,6 +55,19 @@ run reports its actual interaction assertions and inspected screenshots
 separately. A failed recorder is never evidence of continuous capture, and
 neither screenshots nor recording establish an operation latency bound.
 
+For an existing server, take a background screenshot with the observed process ID:
+
+```sh
+ETAF_GUI_CAPTURE_PID=12345 scripts/capture-emacs-window.sh -x /tmp/app-checkpoint.png
+```
+
+Keep the target frame open and non-minimized. Validate a known content change in
+before/after pixels to establish fresh background rendering. Hidden, minimized,
+off-Space and locked-session behavior is not covered by this procedure. Background
+Lisp callbacks and runtime timing do not require application activation; report
+them as background measurements, separately from foreground input-to-display
+latency. Use Emacs-local operations while another app is active, not global input.
+
 ## Continuous resize on the existing server
 
 Use this entry for resize performance investigations instead of copying the