feat: SDK Compliance

.github/workflows/sdk-compliance.yml

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+name: SDK Compliance Tests
+
+permissions:
+  contents: read
+  packages: read
+  pull-requests: write
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+
+jobs:
+  compliance:
+    name: PostHog SDK compliance tests
+    uses: PostHog/posthog-sdk-test-harness/.github/workflows/test-sdk-action.yml@main
+    with:
+      adapter-dockerfile: "sdk_compliance_adapter/Dockerfile"
+      adapter-context: "."
+      test-harness-version: "latest"

sdk_compliance_adapter/Dockerfile

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+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Copy the SDK source code
+COPY posthog/ /app/sdk/posthog/
+COPY setup.py pyproject.toml README.md LICENSE /app/sdk/
+
+# Install the SDK from source
+RUN cd /app/sdk && pip install --no-cache-dir -e .
+
+# Install adapter dependencies
+RUN pip install --no-cache-dir flask python-dateutil
+
+# Copy adapter code
+COPY sdk_compliance_adapter/adapter.py /app/adapter.py
+
+# Expose port 8080
+EXPOSE 8080
+
+# Run the adapter
+CMD ["python", "/app/adapter.py"]

sdk_compliance_adapter/README.md

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+# PostHog Python SDK Test Adapter
+
+This adapter wraps the posthog-python SDK for compliance testing with the [PostHog SDK Test Harness](https://github.com/PostHog/posthog-sdk-test-harness).
+
+## What is This?
+
+This is a simple Flask app that:
+1. Wraps the posthog-python SDK
+2. Exposes a REST API for the test harness to control
+3. Tracks internal SDK state for test assertions
+
+## Running Tests
+
+Tests run automatically in CI via GitHub Actions. See the test harness repo for details.
+
+### Locally with Docker Compose
+
+```bash
+# From the posthog-python/sdk_compliance_adapter directory
+docker-compose up --build --abort-on-container-exit
+```
+
+This will:
+1. Build the Python SDK adapter
+2. Pull the test harness image
+3. Run all compliance tests
+4. Show results
+
+### Manually with Docker
+
+```bash
+# Create network
+docker network create test-network
+
+# Build and run adapter
+docker build -f sdk_compliance_adapter/Dockerfile -t posthog-python-adapter .
+docker run -d --name sdk-adapter --network test-network -p 8080:8080 posthog-python-adapter
+
+# Run test harness
+docker run --rm \
+  --name test-harness \
+  --network test-network \
+  ghcr.io/posthog/sdk-test-harness:latest \
+  run --adapter-url http://sdk-adapter:8080 --mock-url http://test-harness:8081
+
+# Cleanup
+docker stop sdk-adapter && docker rm sdk-adapter
+docker network rm test-network
+```
+
+## Adapter Implementation
+
+See [adapter.py](adapter.py) for the implementation.
+
+The adapter implements the standard SDK adapter interface defined in the [test harness CONTRACT](https://github.com/PostHog/posthog-sdk-test-harness/blob/main/CONTRACT.yaml):
+
+- `GET /health` - Return SDK information
+- `POST /init` - Initialize SDK with config
+- `POST /capture` - Capture an event
+- `POST /flush` - Flush pending events
+- `GET /state` - Return internal state
+- `POST /reset` - Reset SDK state
+
+### Key Implementation Details
+
+**Request Tracking**: The adapter monkey-patches `batch_post` to track all HTTP requests made by the SDK, including retries.
+
+**State Management**: Thread-safe state tracking for events captured vs sent, retry attempts, and errors.
+
+**UUID Tracking**: Extracts and tracks UUIDs from batches to verify deduplication.
+
+## Documentation
+
+For complete documentation on the test harness and how to implement adapters, see:
+- [PostHog SDK Test Harness](https://github.com/PostHog/posthog-sdk-test-harness)
+- [Adapter Implementation Guide](https://github.com/PostHog/posthog-sdk-test-harness/blob/main/ADAPTER_GUIDE.md)