feat(playground): add ETAF example package

Provide a runnable ETAF-only example and an optional UI catalog entry point with lifecycle-safe open/close commands, tests, and bilingual README documentation.

.gitignore

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+*.elc
+tests/*.elc

Makefile

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+EMACS ?= emacs
+LOAD_PATH = -L . -L ../etaf -L ../etaf-ui -L ../emacs-box
+
+.PHONY: all compile test check checkdoc load clean
+
+all: check
+
+compile:
+	rm -f *.elc tests/*.elc
+	$(EMACS) -Q --batch $(LOAD_PATH) --eval '(setq load-prefer-newer t)' \
+		--eval '(load-file "etaf-playground.el")' \
+		--eval '(byte-compile-file "etaf-playground.el")'
+
+test: compile
+	$(EMACS) -Q --batch $(LOAD_PATH) --eval '(setq load-prefer-newer t)' \
+		-l tests/etaf-playground-tests.el -f ert-run-tests-batch-and-exit
+
+load: compile
+	$(EMACS) -Q --batch $(LOAD_PATH) --eval '(require (quote etaf-playground))' \
+		--eval '(princ "etaf-playground load OK\n")'
+
+checkdoc:
+	$(EMACS) -Q --batch --eval '(progn (require (quote checkdoc)) (dolist (file (directory-files "." t)) (when (string-suffix-p ".el" file) (checkdoc-file file))))'
+
+check: checkdoc compile test
+
+clean:
+	rm -f *.elc tests/*.elc

README.md

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+# etaf-playground
+
+`etaf-playground` is the runnable example application for ETAF. The core example depends only on `etaf`; the optional UI example loads `etaf-ui` when requested. It never imports Ebox internals and it is independent from `ebox-playground`.
+
+```elisp
+(require 'etaf-playground)
+(etaf-playground-open)
+```
+
+Run `make check EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs` from this directory.

README.zh-CN.md

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+# etaf-playground
+
+`etaf-playground` 是 ETAF 的可运行示例应用。核心示例只依赖 `etaf`；需要时才通过可选入口加载 `etaf-ui`。它不调用 Ebox 私有实现，也不依赖 `ebox-playground`。
+
+```elisp
+(require 'etaf-playground)
+(etaf-playground-open)
+```
+
+在该目录运行 `make check EMACS=/Applications/Emacs.app/Contents/MacOS/Emacs`。

etaf-playground.el

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+;;; etaf-playground.el --- ETAF public examples -*- lexical-binding: t; -*-
+
+;; SPDX-License-Identifier: GPL-3.0-or-later
+;; Author: ETAF contributors
+;; Version: 0.1.0
+;; Package-Requires: ((emacs "29.1") (etaf "0.1.0"))
+;; URL: https://github.com/ginqi7/etaf-playground
+
+;;; Commentary:
+
+;; This package is a runnable example application, not a second framework
+;; layer.  The core example depends only on ETAF.  The optional catalog demo
+;; loads `etaf-ui' only when its public command is called.
+
+;;; Code:
+
+(require 'cl-lib)
+(require 'etaf)
+
+(defconst etaf-playground-buffer-name "*ETAF Playground*"
+  "Default buffer name used by `etaf-playground-open'.")
+
+;;;###autoload
+(etaf-define-component etaf-playground-counter (&key title)
+  "Render a retained counter titled TITLE."
+  :setup
+  (let ((count (etaf-ref 0 :name 'playground-count)))
+    (lambda ()
+      (etaf-view
+       (column
+        :class "etaf-playground-counter"
+        (text :face 'bold (expr :value title))
+        (text (expr :value (format "Count: %d" (etaf-value count))))
+        (row
+         (text :ref 'decrement :role 'button :tab-index 0
+               :on-press (lambda () (cl-decf (etaf-value count)))
+               " - ")
+         (text :ref 'increment :role 'button :tab-index 0
+               :on-press (lambda () (cl-incf (etaf-value count)))
+               " + ")))))))
+
+;;;###autoload
+(defun etaf-playground-view ()
+  "Return the core ETAF playground View without side effects."
+  (etaf-view
+   (column
+    :class "etaf-playground-root"
+    (text :face 'bold "ETAF Playground")
+    (text :color "#687386"
+          "One grammar: Hosts, Components, props, children, and expr.")
+    (etaf-playground-counter :title "Reactive counter")
+    (text :color "#687386"
+          "Press + or - through the public event dispatch path."))))
+
+;;;###autoload
+(defun etaf-playground-ui-view ()
+  "Return a View demonstrating the optional official `etaf-ui' catalog."
+  (require 'etaf-ui)
+  (etaf-view
+   (column
+    (etaf-panel :title "Official Components"
+     (etaf-button :label "A public Component"
+                  :on-press (lambda () (message "ETAF UI button pressed")))
+     (etaf-checkbox :label "Controlled checkbox"
+                    :on-change (lambda (value)
+                                 (message "Checkbox value: %s" value))))
+    (etaf-playground-counter :title "Core counter"))))
+
+;;;###autoload
+(defun etaf-playground-open (&optional buffer-name)
+  "Mount the core playground in BUFFER-NAME and return its buffer."
+  (interactive)
+  (etaf-mount (or buffer-name etaf-playground-buffer-name)
+              (etaf-playground-view)))
+
+;;;###autoload
+(defun etaf-playground-open-ui (&optional buffer-name)
+  "Mount the playground with the catalog in BUFFER-NAME."
+  (interactive)
+  (etaf-mount (or buffer-name etaf-playground-buffer-name)
+              (etaf-playground-ui-view)))
+
+;;;###autoload
+(defun etaf-playground-close (&optional buffer-name)
+  "Unmount and kill the playground BUFFER-NAME, returning its buffer."
+  (interactive)
+  (let* ((name (or buffer-name etaf-playground-buffer-name))
+         (buffer (get-buffer name)))
+    (when-let ((runtime (and buffer (etaf-runtime-for-buffer buffer))))
+      (etaf-unmount runtime))
+    (when buffer
+      (kill-buffer buffer))
+    buffer))
+
+(provide 'etaf-playground)
+
+;;; etaf-playground.el ends here

tests/etaf-playground-tests.el

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+;;; etaf-playground-tests.el --- ETAF example tests -*- lexical-binding: t; -*-
+
+(require 'ert)
+(require 'etaf-playground)
+
+(ert-deftest etaf-playground-mounts-and-dispatches-core-example ()
+  "Mount the public playground and update its retained counter."
+  (let ((buffer-name " *etaf-playground-test*"))
+    (unwind-protect
+        (progn
+          (etaf-mount buffer-name (etaf-playground-view))
+          (with-current-buffer buffer-name
+            (should (string-match-p "ETAF Playground" (buffer-string)))
+            (should (string-match-p "Count: 0" (buffer-string))))
+          (etaf-dispatch-event (etaf-runtime-for-buffer buffer-name)
+                               'increment 'press)
+          (with-current-buffer buffer-name
+            (should (string-match-p "Count: 1" (buffer-string)))))
+      (when-let ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-unmount runtime))
+      (when-let ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
+(ert-deftest etaf-playground-ui-entry-keeps-catalog-optional ()
+  "Load the catalog only through the optional UI entry point."
+  (require 'etaf-ui)
+  (let ((buffer-name " *etaf-playground-ui-test*"))
+    (unwind-protect
+        (progn
+          (etaf-mount buffer-name (etaf-playground-ui-view))
+          (with-current-buffer buffer-name
+            (should (string-match-p "Official Components" (buffer-string)))
+            (should (string-match-p "Controlled checkbox" (buffer-string)))))
+      (when-let ((runtime (etaf-runtime-for-buffer buffer-name)))
+        (etaf-unmount runtime))
+      (when-let ((buffer (get-buffer buffer-name)))
+        (kill-buffer buffer)))))
+
+(provide 'etaf-playground-tests)
+
+;;; etaf-playground-tests.el ends here