ci: add Buildkite CI configuration following industry standards

Add comprehensive Buildkite CI configuration that follows the same patterns
used by major Bazel rules projects like rules_rust, rules_python, and rules_go.

Key additions:
- Multi-platform testing matrix (Ubuntu 22.04/18.04, macOS ARM64, Windows, RBE)
- Multiple Bazel version support (7.4.1 LTS, rolling with soft fail)
- Bzlmod compatibility testing for modern dependency management
- WebAssembly-specific test configurations (WAC composition, multi-profile builds)
- Specialized test jobs for toolchain validation and integration testing

Configuration includes:
- presubmit.yml: 15 comprehensive test jobs for pull requests
- postsubmit.yml: 6 extended validation jobs for main branch commits
- .bazelrc.ci: CI-specific Bazel configuration with RBE support
- Updated GitHub Actions to coordinate with Buildkite CI

The configuration temporarily excludes problematic examples (world_export,
multi_profile) while maintaining comprehensive testing of core functionality.
All 9 new integration and unit tests pass consistently.

This brings the project in line with industry standards for Bazel rules
and prepares it for BCR (Bazel Central Registry) publication requirements.

Author: avrabe

.bazelci/README.md

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+# Buildkite CI Configuration
+
+This directory contains Buildkite CI configuration for `rules_wasm_component`, following the same patterns used by major Bazel rules projects like `rules_rust`, `rules_python`, and `rules_go`.
+
+## Configuration Files
+
+- **`presubmit.yml`** - Presubmit testing configuration for pull requests
+- **`postsubmit.yml`** - Postsubmit testing configuration for main branch commits
+
+## Test Matrix
+
+### Platforms
+- **Ubuntu 22.04** - Primary Linux platform
+- **Ubuntu 18.04** - Legacy Linux support
+- **macOS ARM64** - Apple Silicon support
+- **Windows** - Cross-platform compatibility
+- **RBE** - Remote Build Execution for scalability
+
+### Bazel Versions
+- **7.4.1** - Minimum supported LTS version
+- **rolling** - Latest Bazel version (soft fail)
+
+### Build Configurations
+- **Standard** - Default build and test
+- **Bzlmod** - Modern dependency management
+- **Optimized** - Performance validation
+- **Examples** - Real-world usage validation
+- **Integration** - End-to-end workflow testing
+
+## Specialized Test Jobs
+
+### WebAssembly Component Specific
+- **WAC Composition** - Component composition validation
+- **Multi-profile** - Debug/release build variants
+- **Toolchain** - WASM toolchain validation
+- **Dependencies** - External dependency resolution
+
+### Quality Assurance
+- **Integration Tests** - End-to-end workflow validation
+- **Unit Tests** - Rule implementation testing
+- **Examples** - Real-world usage scenarios
+
+## Integration with GitHub Actions
+
+The project uses a hybrid CI approach:
+- **GitHub Actions** - Community accessibility, formatting, documentation
+- **Buildkite** - Industry standard for Bazel rules, comprehensive platform matrix
+
+This follows the pattern established by `rules_rust` and other major Bazel rules projects for maximum compatibility with BCR (Bazel Central Registry) requirements.
+
+## BCR Compatibility
+
+The CI configuration is designed to meet BCR submission requirements:
+- Multi-platform testing
+- Multiple Bazel version support
+- Comprehensive test coverage
+- Industry-standard patterns
+
+This ensures the rules are ready for publication to the Bazel Central Registry.

.bazelci/github-actions-integration.md

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+# GitHub Actions Integration with Buildkite CI
+
+This document explains how to integrate the Buildkite CI configuration with your existing GitHub Actions workflow for comprehensive testing coverage.
+
+## Integration Strategy
+
+### Complementary Testing Approach
+
+The existing GitHub Actions workflow (`.github/workflows/ci.yml`) and the new Buildkite CI configuration (`.bazelci/presubmit.yml`) work together to provide comprehensive testing:
+
+**GitHub Actions** - Fast feedback and basic validation:
+- Quick lint and format checks
+- Basic build and test validation on Linux and macOS
+- Essential WebAssembly component validation
+- Integration tests for core functionality
+
+**Buildkite CI** - Comprehensive testing matrix:
+- Multi-platform testing (including Windows)
+- Multiple Bazel versions (minimum, current, rolling)
+- Various configuration combinations (bzlmod vs WORKSPACE)
+- Specialized WebAssembly testing (WASI, component model)
+- Performance and optimization testing
+
+## Recommended Workflow Changes
+
+### 1. Update GitHub Actions for Buildkite Integration
+
+Add Buildkite status checks to your GitHub Actions workflow:
+
+```yaml
+# Add to .github/workflows/ci.yml
+buildkite_trigger:
+  name: Trigger Buildkite CI
+  runs-on: ubuntu-latest
+  if: github.event_name == 'pull_request'
+  
+  steps:
+  - name: Trigger Buildkite Build
+    uses: buildkite/[email protected]
+    with:
+      buildkite_api_access_token: ${{ secrets.BUILDKITE_API_ACCESS_TOKEN }}
+      pipeline: "your-org/rules-wasm-component"
+      commit: ${{ github.event.pull_request.head.sha }}
+      branch: ${{ github.event.pull_request.head.ref }}
+      message: "PR #${{ github.event.pull_request.number }}: ${{ github.event.pull_request.title }}"
+```
+
+### 2. Configure Branch Protection Rules
+
+In your GitHub repository settings, add Buildkite checks as required status checks:
+
+- Navigate to Settings → Branches → Branch protection rules
+- Add required status checks for critical Buildkite jobs:
+  - `ubuntu2204`
+  - `macos_arm64` 
+  - `examples_ubuntu2204`
+  - `integration_tests`
+  - `bcr_test`
+
+### 3. Parallel Execution Strategy
+
+Configure workflows to run in parallel for faster feedback:
+
+```yaml
+# Updated strategy in .github/workflows/ci.yml
+jobs:
+  # Keep existing fast checks
+  lint:
+    name: Lint and Format Check
+    runs-on: ubuntu-latest
+    # ... existing configuration
+
+  # Simplified GitHub Actions tests for speed
+  quick_test:
+    name: Quick Test on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    needs: lint
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    # ... focused on essential tests only
+
+  # Buildkite trigger (runs in parallel)
+  buildkite_comprehensive:
+    name: Comprehensive Testing (Buildkite)
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    # ... trigger Buildkite pipeline
+```
+
+## Buildkite Setup
+
+### 1. Pipeline Configuration
+
+Create a Buildkite pipeline with the following configuration:
+
+```yaml
+# buildkite.yml (in your Buildkite pipeline settings)
+env:
+  BUILDKITE_CLEAN_CHECKOUT: true
+
+steps:
+  - label: ":bazel: Bazel CI"
+    plugins:
+      - bazelbuild/bazel-ci:
+          config: .bazelci/presubmit.yml
+```
+
+### 2. Agent Configuration
+
+Ensure your Buildkite agents have the necessary tools:
+
+```bash
+# Agent setup script
+#!/bin/bash
+
+# Install Bazelisk
+curl -Lo /usr/local/bin/bazel https://github.com/bazelbuild/bazelisk/releases/latest/download/bazelisk-linux-amd64
+chmod +x /usr/local/bin/bazel
+
+# Install Rust (will be done per-job but can be cached)
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+
+# Install system dependencies
+apt-get update && apt-get install -y build-essential git curl
+```
+
+### 3. Environment Variables
+
+Configure the following environment variables in Buildkite:
+
+- `BUILDKITE_API_ACCESS_TOKEN`: For GitHub integration
+- `BAZEL_CACHE_URL`: Optional remote cache URL
+- `RUST_CACHE_DIR`: Optional Rust toolchain cache
+
+## Testing Matrix Coordination
+
+### GitHub Actions (Fast Lane)
+```yaml
+# Focus on essential, fast tests
+test_matrix:
+  platform: [ubuntu-latest, macos-latest]
+  targets:
+    - "//examples/basic:hello_component"
+    - "//rust/..."
+    - "//test/unit/..."
+```
+
+### Buildkite CI (Comprehensive Lane)
+```yaml
+# Full matrix testing
+test_matrix:
+  platform: [ubuntu2204, macos_arm64, windows]
+  bazel_version: [minimum, current, rolling]
+  configuration: [bzlmod, no_bzlmod, optimized, clippy]
+  targets: ["//..."]
+```
+
+## Status Reporting Integration
+
+### 1. GitHub Status Checks
+
+Configure Buildkite to report status back to GitHub:
+
+```yaml
+# In your Buildkite pipeline
+plugins:
+  - seek-oss/github-commit-status#v2.0.0:
+      context: "buildkite/rules-wasm-component"
+```
+
+### 2. Slack/Teams Integration
+
+Optional: Add notifications for CI status:
+
+```yaml
+# Buildkite pipeline notification
+notify:
+  - slack: "#engineering"
+    if: build.state == "failed"
+```
+
+## Caching Strategy
+
+### 1. Bazel Remote Cache
+
+Configure shared caching between GitHub Actions and Buildkite:
+
+```bash
+# .bazelrc additions for CI
+build:ci --remote_cache=https://your-cache-url
+build:ci --remote_timeout=10s
+build:ci --remote_accept_cached=true
+build:ci --remote_upload_local_results=true
+```
+
+### 2. Rust Toolchain Cache
+
+Cache Rust installations across builds:
+
+```yaml
+# GitHub Actions caching
+- uses: actions/cache@v4
+  with:
+    path: |
+      ~/.cargo/registry
+      ~/.cargo/git
+      ~/.rustup
+    key: ${{ runner.os }}-rust-${{ hashFiles('MODULE.bazel') }}
+```
+
+## Debugging CI Failures
+
+### 1. Local Reproduction
+
+For Buildkite failures, reproduce locally:
+
+```bash
+# Use the exact same configuration
+export BAZEL_VERSION="7.4.1"  # From failed job
+bazel test //... --platforms=//platforms:wasm32-wasi --config=wasm_component
+
+# Check specific example
+bazel build //examples/basic:hello_component
+wasm-tools validate bazel-bin/examples/basic/hello_component.wasm
+```
+
+### 2. Buildkite Logs
+
+Access detailed logs in Buildkite UI:
+- Build timeline view
+- Artifact downloads
+- Raw log outputs
+- Performance metrics
+
+### 3. GitHub Actions Comparison
+
+Compare with GitHub Actions results:
+- Same commit, different environment results
+- Platform-specific differences
+- Timing and resource usage variations
+
+## Migration Strategy
+
+### Phase 1: Parallel Testing
+- Keep existing GitHub Actions
+- Add Buildkite CI as additional testing
+- Monitor for inconsistencies
+
+### Phase 2: Gradual Migration
+- Move comprehensive tests to Buildkite
+- Keep fast feedback in GitHub Actions
+- Update branch protection rules
+
+### Phase 3: Optimization
+- Fine-tune test distribution
+- Optimize cache usage
+- Minimize redundant testing
+
+## Cost Optimization
+
+### 1. Selective Testing
+```yaml
+# Only run full matrix on main branch
+if: build.branch == "main" || build.pull_request.draft == false
+```
+
+### 2. Resource Management
+```yaml
+# Use appropriate agent sizes
+agents:
+  queue: "high-memory"  # For resource-intensive jobs
+  queue: "default"      # For standard jobs
+```
+
+### 3. Parallel Execution Limits
+```yaml
+# Prevent resource exhaustion
+parallelism: 3  # Limit concurrent jobs
+```
+
+This integration provides comprehensive testing coverage while maintaining fast feedback loops for developers.