Added AGENTS.md for improved vibe coding experience

Author: wisskid

AGENTS.md

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+# AGENTS.md
+
+## Project
+
+Smarty v5 — PHP template engine. Single Composer package (`smarty/smarty`), namespace `Smarty\`, source in `src/`, autoloaded via PSR-4. Supports PHP 7.2–8.5.
+
+## Commands
+
+```bash
+# Install dependencies
+composer install
+
+# Regenerate lexers and parsers (required before tests; CI runs this)
+make -B
+
+# Run all tests
+php ./vendor/phpunit/phpunit/phpunit
+
+# Run a single test file
+php ./vendor/phpunit/phpunit/phpunit tests/UnitTests/TemplateSource/TagTests/If/CompileIfTest.php
+
+# Run tests matching a PHPUnit group
+php ./vendor/phpunit/phpunit/phpunit --group 20221124
+
+# Run tests excluding slow group
+php ./vendor/phpunit/phpunit/phpunit --exclude-group slow
+```
+
+There is no linter or static analysis configured. No typecheck step.
+
+## Generated code — do not hand-edit
+
+Four files are generated from grammar/lexer definitions via `make`:
+
+| Source (edit this) | Generated (do not edit) |
+|---|---|
+| `src/Lexer/TemplateLexer.plex` | `src/Lexer/TemplateLexer.php` |
+| `src/Lexer/ConfigfileLexer.plex` | `src/Lexer/ConfigfileLexer.php` |
+| `src/Parser/TemplateParser.y` | `src/Parser/TemplateParser.php` |
+| `src/Parser/ConfigfileParser.y` | `src/Parser/ConfigfileParser.php` |
+
+After editing a `.plex` or `.y` file, run `make -B` to regenerate. The generators require the `smarty/smarty-lexer` dev dependency.
+
+## Architecture
+
+- `src/Smarty.php` — main class, extends `TemplateBase`. Version constant: `Smarty::SMARTY_VERSION`.
+- `src/Compile/`, `src/Compiler/` — template compilation pipeline.
+- `src/Lexer/`, `src/Parser/` — lexer/parser (generated, see above).
+- `src/Extension/` — extension system (`ExtensionInterface`, `CoreExtension`, `DefaultExtension`, `BCPluginsAdapter`).
+- `src/Runtime/` — runtime helpers (foreach, capture, inheritance, tpl functions).
+- `src/Resource/`, `src/Cacheresource/` — template resource and cache resource handlers.
+- `src/BlockHandler/`, `src/FunctionHandler/`, `src/Filter/` — built-in tags, functions, and filters.
+- `libs/Smarty.class.php` — non-Composer autoload stub. Points to `src/`. Not the main source.
+- `src/functions.php` — global helper functions, always loaded via Composer `files` autoload.
+
+## Tests
+
+- Framework: PHPUnit 7.5/8.5 (bootstrap: `tests/Bootstrap.php`).
+- All tests extend `PHPUnit_Smarty` (defined in `tests/PHPUnit_Smarty.php`), which provides `setUpSmarty($dir)`.
+- Test suite root: `tests/UnitTests/`. Typical test `setUp()` calls `$this->setUpSmarty(__DIR__)`.
+- Each test directory may have its own `templates/`, `configs/` subdirectories. Compiled output goes to `templates_c/` and `cache/` (auto-created by the test harness).
+- Three test files are excluded in `phpunit.xml`: Memcache, APC, and HttpModifiedSince tests (require external services).
+- Tests needing MySQL/PDO are gated by constants in `tests/Config.php` (disabled by default).
+
+## CI
+
+GitHub Actions (`.github/workflows/ci.yml`): matrix of PHP 7.2–8.5 on ubuntu + windows. Steps: `composer install` → `make -B` → `phpunit`. No deploy step.
+
+## Docs
+
+Markdown in `docs/`, built with mkdocs + Material theme. Preview: `mkdocs serve`. Published via `mike deploy 5.x`.
+
+## Release
+
+`./make-release.sh <version>` — only v5.x.x. Updates changelog and version constant, creates a merge commit and tag on `master`.