feat: L2 ActivityPub server

- Registry for owned assets
- ActivityPub endpoints (webfinger, actor, inbox, outbox)
- Create activities with signatures
- Record L1 runs as owned assets with provenance
- Federation support (followers, inbox)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

README.md

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+# Art DAG L2 Server - ActivityPub
+
+Ownership registry and ActivityPub federation for Art DAG.
+
+## What it does
+
+- **Registry**: Maintains owned assets with content hashes
+- **Activities**: Creates signed ownership claims (Create activities)
+- **Federation**: ActivityPub endpoints for follow/share
+- **L1 Integration**: Records completed L1 runs as owned assets
+
+## Setup
+
+```bash
+pip install -r requirements.txt
+
+# Configure (optional - defaults shown)
+export ARTDAG_DOMAIN=artdag.rose-ash.com
+export ARTDAG_USER=giles
+export ARTDAG_DATA=~/.artdag/l2
+export ARTDAG_L1=http://localhost:8100
+
+# Start server
+python server.py
+```
+
+## API Endpoints
+
+### Server Info
+| Method | Path | Description |
+|--------|------|-------------|
+| GET | `/` | Server info |
+
+### ActivityPub
+| Method | Path | Description |
+|--------|------|-------------|
+| GET | `/.well-known/webfinger?resource=acct:user@domain` | Actor discovery |
+| GET | `/users/{username}` | Actor profile |
+| GET | `/users/{username}/outbox` | Published activities |
+| POST | `/users/{username}/inbox` | Receive activities |
+| GET | `/users/{username}/followers` | Followers list |
+| GET | `/objects/{content_hash}` | Get object by hash |
+
+### Registry
+| Method | Path | Description |
+|--------|------|-------------|
+| GET | `/registry` | Full registry |
+| GET | `/registry/{name}` | Get asset by name |
+| POST | `/registry` | Register new asset |
+| POST | `/registry/record-run` | Record L1 run as owned asset |
+
+## Example Usage
+
+### Register an asset
+```bash
+curl -X POST http://localhost:8200/registry \
+  -H "Content-Type: application/json" \
+  -d '{
+    "name": "my-video",
+    "content_hash": "abc123...",
+    "asset_type": "video",
+    "tags": ["art", "generated"]
+  }'
+```
+
+### Record an L1 run
+```bash
+curl -X POST http://localhost:8200/registry/record-run \
+  -H "Content-Type: application/json" \
+  -d '{
+    "run_id": "uuid-from-l1",
+    "output_name": "my-rendered-video"
+  }'
+```
+
+### Discover actor (WebFinger)
+```bash
+curl "http://localhost:8200/.well-known/webfinger?resource=acct:giles@artdag.rose-ash.com"
+```
+
+### Get actor profile
+```bash
+curl -H "Accept: application/activity+json" http://localhost:8200/users/giles
+```
+
+## Data Storage
+
+Data stored in `~/.artdag/l2/`:
+- `registry.json` - Asset registry
+- `activities.json` - Signed activities
+- `actor.json` - Actor profile
+- `followers.json` - Followers list
+
+## Architecture
+
+```
+L2 Server (port 8200)
+    │
+    ├── POST /registry → Register asset → Create activity → Sign
+    │
+    ├── POST /registry/record-run → Fetch L1 run → Register output
+    │       │
+    │       └── GET L1_SERVER/runs/{id}
+    │
+    ├── GET /users/{user}/outbox → Return signed activities
+    │
+    └── POST /users/{user}/inbox → Receive Follow requests
+```