docs: add README with installation and usage instructions

Made-with: Cursor

README.md

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+# cursor-flasher
+
+A macOS daemon that flashes a pulsing border around Cursor IDE windows when the AI agent is waiting for your input. Optionally plays a system sound.
+
+## Prerequisites
+
+- macOS
+- Python 3.10+
+- **Accessibility permission** granted to your terminal (System Settings → Privacy & Security → Accessibility)
+
+## Installation
+
+```bash
+git clone <repo-url> && cd cursor-flasher
+pip install -e ".[dev]"
+```
+
+## Usage
+
+```bash
+# Start the daemon (backgrounds automatically)
+cursor-flasher start
+
+# Start in foreground (useful for debugging)
+cursor-flasher start --foreground
+
+# Check if the daemon is running
+cursor-flasher status
+
+# Stop the daemon
+cursor-flasher stop
+```
+
+## How It Works
+
+1. Polls Cursor's macOS accessibility tree every 500ms
+2. Detects agent state by looking for specific UI elements (Stop/Accept/Reject buttons)
+3. When the agent finishes and is waiting for input, shows a pulsing amber border around **only the window(s) that need attention**
+4. Plays a system sound (default: "Glass")
+5. Dismisses automatically when the agent starts working again, or after a timeout
+
+## Configuration
+
+Create `~/.cursor-flasher/config.yaml` to customize:
+
+```yaml
+pulse:
+  color: "#FF9500"    # Border color (hex)
+  width: 4            # Border thickness (px)
+  speed: 1.5          # Pulse cycle duration (seconds)
+  opacity_min: 0.3    # Minimum pulse opacity
+  opacity_max: 1.0    # Maximum pulse opacity
+
+sound:
+  enabled: true       # Play sound on trigger
+  name: "Glass"       # macOS system sound name
+  volume: 0.5         # Volume (0.0 - 1.0)
+
+detection:
+  poll_interval: 0.5  # Seconds between accessibility tree polls
+  cooldown: 3.0       # Seconds before re-triggering after dismissal
+
+timeout:
+  auto_dismiss: 300   # Auto-hide overlay after N seconds
+```
+
+All values are optional — defaults are used for anything not specified.
+
+## Troubleshooting
+
+**"Cursor is not running" / no detection:**
+Make sure Cursor is open. The daemon looks for the process by bundle ID.
+
+**No overlay appears:**
+Grant Accessibility permission to your terminal app: System Settings → Privacy & Security → Accessibility. You may need to restart the terminal after granting.
+
+**Overlay appears on wrong windows:**
+Detection is per-window — only windows with active approval prompts (Accept, Reject, Run, etc.) should flash. If you see false positives, the detection patterns may need tuning for your Cursor version. Check `scripts/dump_a11y_tree.py` to inspect the accessibility tree.
+
+## Development
+
+```bash
+# Run tests
+pytest tests/ -v
+
+# Dump Cursor's accessibility tree (for debugging detection)
+python scripts/dump_a11y_tree.py --depth 8
+
+# Manual overlay test (flashes all windows for 10 seconds)
+python scripts/test_overlay.py
+
+# Manual overlay test (only windows needing attention)
+python scripts/test_overlay.py --per-window
+```