docs: add AGENTS.md for AI coding agents

AGENTS.md

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+# DSL DevKit - Agent Guidelines
+
+This document helps AI coding agents work effectively with the DSL DevKit codebase.
+
+## Project Overview
+
+- **Type**: Multi-module Tycho/Eclipse/OSGi project (~65 modules)
+- **Purpose**: DSL development toolkit built on Xtext
+- **Java**: 21
+- **Maven**: 3.9+
+- **Tycho**: 5.0.2
+- **Xtext/Xtend**: 2.41.0
+
+## Key Directories
+
+| Directory | Purpose |
+|-----------|---------|
+| `ddk-parent/` | Parent POM, build entry point |
+| `ddk-configuration/` | Quality tool configs (PMD, Checkstyle, SpotBugs) |
+| `ddk-target/` | Eclipse target platform definition |
+| `ddk-repository/` | P2 update site |
+| `com.avaloq.tools.ddk.*` | Source modules |
+| `*.test` | Test modules |
+
+## Build Commands
+
+```bash
+# Full CI build (Linux - requires xvfb for UI tests)
+xvfb-run mvn clean verify checkstyle:check pmd:pmd pmd:cpd pmd:check pmd:cpd-check spotbugs:check -f ./ddk-parent/pom.xml --batch-mode --fail-at-end
+
+# Windows build
+mvn clean verify -f ./ddk-parent/pom.xml
+
+# Quick build without quality checks
+mvn clean verify -f ./ddk-parent/pom.xml -DskipTests
+
+# Build specific module
+mvn clean verify -f ./ddk-parent/pom.xml -pl :com.avaloq.tools.ddk.xtext
+
+# Run only quality checks (after initial build)
+mvn checkstyle:check pmd:check spotbugs:check -f ./ddk-parent/pom.xml
+```
+
+**Important**: Set `WORKSPACE` environment variable to project root before building:
+```bash
+export WORKSPACE=$(pwd)
+```
+
+## Quality Tools
+
+### PMD (7.21.0)
+- **Ruleset**: `ddk-configuration/pmd/ruleset.xml`
+- **Plugin**: 3.28.0
+- Excludes: `src-gen/`, `src-model/`, `xtend-gen/`
+
+### Checkstyle (13.0.0)
+- **Config**: `ddk-configuration/checkstyle/avaloq.xml`
+- **Test config**: `ddk-configuration/checkstyle/avaloq-test.xml`
+- Only checks `src/` directory
+
+### SpotBugs (4.9.8)
+- **Exclusions**: `ddk-configuration/findbugs/exclusion-filter.xml`
+- Max rank: 15, Threshold: Low
+
+## Testing
+
+- **Framework**: JUnit 5 with Tycho Surefire
+- **Timeout**: 30 minutes (1800 seconds)
+- **Main test module**: `com.avaloq.tools.ddk.xtext.test`
+- **UI tests**: Require virtual display (xvfb on Linux)
+
+Tests are disabled by default and activated only in test bundles.
+
+## Code Patterns
+
+### Dependencies
+- Use `MANIFEST.MF` for OSGi bundle dependencies (not pom.xml)
+- Bundle dependencies defined in `META-INF/MANIFEST.MF`
+
+### Generated Code
+These directories contain generated code - do not edit manually:
+- `src-gen/` - Xtext generated sources
+- `src-model/` - EMF model generated sources
+- `xtend-gen/` - Xtend transpiled Java sources
+
+### Xtend
+- `.xtend` files in `src/` compile to Java in `xtend-gen/`
+- Xtend version: 2.41.0
+
+## Common Tasks
+
+### Adding a New Module
+1. Create module directory with standard structure
+2. Add `META-INF/MANIFEST.MF` for OSGi metadata
+3. Add `build.properties` for Tycho
+4. Add module to `ddk-parent/pom.xml` modules list
+5. Follow naming convention: `com.avaloq.tools.ddk.<component>`
+
+### Fixing PMD Violations
+1. Check ruleset at `ddk-configuration/pmd/ruleset.xml`
+2. Violations in generated code (`src-gen/`, `xtend-gen/`) are excluded
+3. Run `mvn pmd:check -f ./ddk-parent/pom.xml` to verify fixes
+
+### Fixing Checkstyle Violations
+1. Check config at `ddk-configuration/checkstyle/avaloq.xml`
+2. Run `mvn checkstyle:check -f ./ddk-parent/pom.xml` to verify fixes
+
+### Running Specific Tests
+```bash
+# Run tests for a specific module
+mvn verify -f ./ddk-parent/pom.xml -pl :com.avaloq.tools.ddk.xtext.test
+
+# On Linux, wrap with xvfb for UI tests
+xvfb-run mvn verify -f ./ddk-parent/pom.xml -pl :com.avaloq.tools.ddk.xtext.test
+```
+
+## CI/CD
+
+- **Platform**: GitHub Actions
+- **Runner**: Ubuntu 24.04
+- **Workflow**: `.github/workflows/verify.yml`
+- Triggers on: push to master, pull requests