feature/capability-based-deps (#53)

Reviewed-on: klubhaus/sideline#53
Co-authored-by: David Gwilliam <dhgwilliam@gmail.com>
Co-committed-by: David Gwilliam <dhgwilliam@gmail.com>

.opencode/skills/mainline-sources/SKILL.md

@@ -0,0 +1,87 @@
+---
+name: mainline-sources
+description: Adding new RSS feeds and data sources to Mainline
+compatibility: opencode
+metadata:
+  audience: developers
+  source_type: codebase
+---
+
+## What This Skill Covers
+
+This skill covers how to add new data sources (RSS feeds, poetry) to Mainline.
+
+## Key Concepts
+
+### Feeds Dictionary (engine/sources.py)
+
+All feeds are defined in a simple dictionary:
+
+```python
+FEEDS = {
+    "Feed Name": "https://example.com/feed.xml",
+    # Category comments help organize:
+    # Science & Technology
+    # Economics & Business
+    # World & Politics
+    # Culture & Ideas
+}
+```
+
+### Poetry Sources
+
+Project Gutenberg URLs for public domain literature:
+
+```python
+POETRY_SOURCES = {
+    "Author Name": "https://www.gutenberg.org/cache/epub/1234/pg1234.txt",
+}
+```
+
+### Language & Script Mapping
+
+The sources.py also contains language/script detection mappings used for auto-translation and font selection.
+
+## Adding a New RSS Feed
+
+1. Edit `engine/sources.py`
+2. Add entry to `FEEDS` dict under appropriate category:
+   ```python
+   "My Feed": "https://example.com/feed.xml",
+   ```
+3. The feed will be automatically discovered on next run
+
+### Feed Requirements
+
+- Must be valid RSS or Atom XML
+- Should have `<title>` elements for items
+- Must be HTTP/HTTPS accessible
+
+## Adding Poetry Sources
+
+1. Edit `engine/sources.py`
+2. Add to `POETRY_SOURCES` dict:
+   ```python
+   "Author": "https://www.gutenberg.org/cache/epub/XXXX/pgXXXX.txt",
+   ```
+
+### Poetry Requirements
+
+- Plain text (UTF-8)
+- Project Gutenberg format preferred
+- No DRM-protected sources
+
+## Data Flow
+
+Feeds are fetched via `engine/fetch.py`:
+- `fetch_feed(url)` - Fetches and parses RSS/Atom
+- Results cached for fast restarts
+- Filtered via `engine/filter.py` for content cleaning
+
+## Categories
+
+Organize new feeds by category using comments:
+- Science & Technology
+- Economics & Business  
+- World & Politics
+- Culture & Ideas