[PromptTemplate] Add new component with extensible renderer architecture

src/prompt-template/.gitattributes

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+/.gitattributes export-ignore
+/.gitignore export-ignore
+/phpstan.dist.neon export-ignore
+/phpunit.xml.dist export-ignore
+/tests export-ignore
+/AGENTS.md export-ignore
+/CLAUDE.md export-ignore

src/prompt-template/AGENTS.md

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+# AGENTS.md
+
+AI agent guidance for the Prompt Template component.
+
+## Component Overview
+
+Extensible prompt templating system with pluggable rendering strategies. Provides simple variable substitution by default and optional Symfony Expression Language integration for advanced use cases.
+
+## Architecture
+
+### Core Classes
+- **PromptTemplate**: Main implementation with renderer injection
+- **PromptTemplateInterface**: Core contract for template implementations
+- **RendererInterface**: Strategy interface for rendering implementations
+- **StringRenderer**: Default renderer using simple {variable} replacement (zero dependencies)
+- **ExpressionRenderer**: Optional renderer using Symfony Expression Language for advanced expressions
+
+### Key Features
+- **Zero Core Dependencies**: Only requires PHP 8.2+
+- **Strategy Pattern**: Pluggable renderer system for extensibility
+- **Simple by Default**: Basic {variable} replacement out of the box
+- **Advanced Optional**: Expression Language for power users
+- **Immutable**: readonly classes ensure thread-safety
+
+### Key Directories
+- `src/`: Source code with main classes
+- `src/Renderer/`: Renderer implementations
+- `src/Exception/`: Component-specific exceptions (factory pattern)
+- `tests/`: Comprehensive test suite mirroring src structure
+- `tests/Renderer/`: Tests for each renderer
+
+## Essential Commands
+
+### Testing
+```bash
+vendor/bin/phpunit
+vendor/bin/phpunit tests/PromptTemplateTest.php
+vendor/bin/phpunit --coverage-html coverage
+```
+
+### Code Quality
+```bash
+vendor/bin/phpstan analyse
+cd ../../.. && vendor/bin/php-cs-fixer fix src/prompt-template/
+```
+
+### Dependencies
+```bash
+composer install
+composer require symfony/expression-language  # For ExpressionRenderer
+```
+
+## Usage Patterns
+
+### Default Renderer
+```php
+$template = new PromptTemplate('Hello {name}!');
+echo $template->format(['name' => 'World']);
+```
+
+### Expression Renderer
+```php
+$renderer = new ExpressionRenderer();
+$template = new PromptTemplate('Total: {price * quantity}', $renderer);
+echo $template->format(['price' => 10, 'quantity' => 5]);
+```
+
+### Custom Renderer
+```php
+class MyRenderer implements RendererInterface {
+    public function render(string $template, array $values): string {
+        // Custom implementation
+    }
+}
+
+$template = new PromptTemplate($template, new MyRenderer());
+```
+
+## Testing Patterns
+
+- PHPUnit 11.5+ with strict configuration
+- Test fixtures follow monorepo patterns
+- Each renderer has dedicated test class
+- Integration tests verify renderer injection
+- Component-specific exception testing using factory pattern
+- Prefer `self::assert*` over `$this->assert*`
+
+## Development Notes
+
+- Add `@author` tags to new classes
+- Use component-specific exceptions from `src/Exception/` with factory pattern
+- Follow Symfony coding standards with `@Symfony` PHP CS Fixer rules
+- Component is experimental (BC breaks possible)
+- StringRenderer must remain dependency-free
+- ExpressionRenderer requires symfony/expression-language
+- All classes use readonly for immutability

src/prompt-template/CHANGELOG.md

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+# CHANGELOG
+
+## 0.1.0
+
+**Initial release**
+
+- Introduced `PromptTemplate` for prompt template management
+- Added `StringRenderer` for simple {variable} replacement (zero dependencies)
+- Added `ExpressionRenderer` for Symfony Expression Language integration
+- Implemented extensible renderer strategy pattern via `RendererInterface`
+- Added comprehensive exception hierarchy
+- Provides static factory methods for convenient template creation

src/prompt-template/CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this component.
+
+## Component Overview
+
+This is the Prompt Template component of the Symfony AI monorepo - an extensible prompt templating system with pluggable rendering strategies. It provides simple variable substitution by default and optional Symfony Expression Language integration for advanced use cases.
+
+## Architecture
+
+### Core Classes
+
+- **PromptTemplate**: Main implementation with renderer injection
+- **PromptTemplateInterface**: Core contract for template implementations
+- **RendererInterface**: Strategy interface for rendering implementations
+- **StringRenderer**: Default renderer using simple {variable} replacement (zero dependencies)
+- **ExpressionRenderer**: Optional renderer using Symfony Expression Language for advanced expressions
+
+### Key Features
+
+- **Zero Core Dependencies**: Only requires PHP 8.2+
+- **Strategy Pattern**: Pluggable renderer system for extensibility
+- **Simple by Default**: Basic {variable} replacement out of the box
+- **Advanced Optional**: Expression Language for power users
+- **Immutable**: readonly classes ensure thread-safety
+
+### Key Directories
+
+- `src/`: Source code with main classes
+- `src/Renderer/`: Renderer implementations
+- `src/Exception/`: Component-specific exceptions
+- `tests/`: Comprehensive test suite mirroring src structure
+- `tests/Renderer/`: Tests for each renderer
+
+## Development Commands
+
+### Testing
+
+```bash
+# Run all tests
+vendor/bin/phpunit
+
+# Run specific test
+vendor/bin/phpunit tests/PromptTemplateTest.php
+
+# Run with coverage
+vendor/bin/phpunit --coverage-html coverage
+```
+
+### Code Quality
+
+```bash
+# Run PHPStan static analysis
+vendor/bin/phpstan analyse
+
+# Fix code style (run from project root)
+cd ../../.. && vendor/bin/php-cs-fixer fix src/prompt-template/
+```
+
+### Installing Dependencies
+
+```bash
+# Install dependencies
+composer install
+
+# Install with expression language
+composer require symfony/expression-language
+```
+
+## Testing Architecture
+
+- Uses PHPUnit 11.5+ with strict configuration
+- Test fixtures follow monorepo patterns
+- Each renderer has dedicated test class
+- Integration tests verify renderer injection
+- Component-specific exception testing
+- Prefer `self::assert*` over `$this->assert*`
+
+## Usage Patterns
+
+### Default Renderer
+
+```php
+$template = new PromptTemplate('Hello {name}!');
+echo $template->format(['name' => 'World']);
+```
+
+### Expression Renderer
+
+```php
+$renderer = new ExpressionRenderer();
+$template = new PromptTemplate('Total: {price * quantity}', $renderer);
+echo $template->format(['price' => 10, 'quantity' => 5]);
+```
+
+### Custom Renderer
+
+```php
+class MyRenderer implements RendererInterface {
+    public function render(string $template, array $values): string {
+        // Custom implementation
+    }
+}
+
+$template = new PromptTemplate($template, new MyRenderer());
+```
+
+## Development Notes
+
+- All new classes should have `@author` tags
+- Use component-specific exceptions from `src/Exception/`
+- Follow Symfony coding standards with `@Symfony` PHP CS Fixer rules
+- Component is marked as experimental (BC breaks possible)
+- StringRenderer must remain dependency-free
+- ExpressionRenderer requires symfony/expression-language
+- All classes use readonly for immutability

src/prompt-template/LICENSE

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+Copyright (c) 2025-present Fabien Potencier
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is furnished
+to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

src/prompt-template/README.md

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+# Symfony AI Prompt Template Component
+
+**This Component is [experimental](https://github.com/symfony/ai?tab=readme-ov-file#component-status). Expect breaking changes in minor and patch versions.**
+
+PHP library for prompt template management with extensible rendering strategies.
+
+## Installation
+
+```bash
+composer require symfony/ai-prompt-template
+```
+
+For advanced expression-based rendering:
+
+```bash
+composer require symfony/expression-language
+```
+
+## Basic Usage
+
+### Simple Variable Replacement (Default)
+
+```php
+use Symfony\AI\PromptTemplate\PromptTemplate;
+
+$template = new PromptTemplate('Hello {name}!');
+echo $template->format(['name' => 'World']); // "Hello World!"
+
+// Using static factory
+$template = PromptTemplate::fromString(<<<'PROMPT'
+You are a helpful assistant.
+
+User: {user}
+Query: {query}
+PROMPT);
+
+echo $template->format([
+    'user' => 'Alice',
+    'query' => 'What is AI?',
+]);
+```
+
+The default `StringRenderer` performs simple `{variable}` replacement with zero external dependencies.
+
+### Advanced Expression-Based Rendering
+
+Install `symfony/expression-language` to use the `ExpressionRenderer`:
+
+```php
+use Symfony\AI\PromptTemplate\PromptTemplate;
+use Symfony\AI\PromptTemplate\Renderer\ExpressionRenderer;
+
+$renderer = new ExpressionRenderer();
+$template = new PromptTemplate('Total: {price * quantity}', $renderer);
+echo $template->format(['price' => 10, 'quantity' => 5]); // "Total: 50"
+
+// Conditional expressions
+$template = PromptTemplate::fromStringWithRenderer(
+    'Status: {age >= 18 ? "adult" : "minor"}',
+    new ExpressionRenderer()
+);
+echo $template->format(['age' => 25]); // "Status: adult"
+
+// Object property access
+$template = new PromptTemplate('Name: {user.name}', $renderer);
+echo $template->format(['user' => $userObject]); // "Name: Alice"
+```
+
+### Custom Renderers
+
+Implement `RendererInterface` to create custom rendering strategies:
+
+```php
+use Symfony\AI\PromptTemplate\Renderer\RendererInterface;
+
+class MustacheRenderer implements RendererInterface
+{
+    public function render(string $template, array $values): string
+    {
+        foreach ($values as $key => $value) {
+            $template = str_replace('{{'.$key.'}}', (string) $value, $template);
+        }
+        return $template;
+    }
+}
+
+$template = new PromptTemplate('Hello {{name}}!', new MustacheRenderer());
+echo $template->format(['name' => 'World']); // "Hello World!"
+```
+
+## Available Renderers
+
+### StringRenderer (Default)
+
+- Simple `{variable}` placeholder replacement
+- Validates variable names and values
+- Zero external dependencies
+- Supports strings, numbers, and `\Stringable` objects
+
+### ExpressionRenderer (Optional)
+
+Requires `symfony/expression-language`
+
+- Variable access: `{user.name}`
+- Math operations: `{price * quantity}`
+- Conditionals: `{age > 18 ? "adult" : "minor"}`
+- String concatenation: `{firstName ~ " " ~ lastName}`
+- Array access: `{items[0]}`
+- Custom functions via `ExpressionLanguage`
+
+## API Reference
+
+### PromptTemplate
+
+```php
+// Constructor
+new PromptTemplate(string $template, ?RendererInterface $renderer = null)
+
+// Methods
+$template->format(array $values = []): string
+$template->getTemplate(): string
+(string) $template // Returns template string
+
+// Static factories
+PromptTemplate::fromString(string $template): self
+PromptTemplate::fromStringWithRenderer(string $template, RendererInterface $renderer): self
+```
+
+### RendererInterface
+
+```php
+interface RendererInterface
+{
+    public function render(string $template, array $values): string;
+}
+```
+
+## Resources
+
+- [Main Repository](https://github.com/symfony/ai)
+- [Report Issues](https://github.com/symfony/ai/issues)
+- [Submit Pull Requests](https://github.com/symfony/ai/pulls)