# Implementation: Additive Extension Model

## Summary

Replaced the diff/merge upgrade process with an additive extension model. Projects no longer copy framework files — they provide overrides via `.agent.md`, `.rules.md`, and an optional `extensions/` directory.

## Changes Made

### `prompts/orchestrate.md`
- Base framework files (prompts, contracts, scripts) now always read from `~/.automaton/`
- Projects provide additive extensions under `{project}/.automaton/extensions/`
- Extension read order: project extensions loaded after (or before for scripts) corresponding global files
- `.agent.md` and `.rules.md` remain layered (project override first)

### `prompts/onboarding.md`
- Removed the diff/merge "Project Upgrade" section
- Simplified to create minimal `.agent.md` and `.rules.md` if missing
- Documents the `extensions/` directory pattern
- Explicitly states projects should never copy framework files

### `scripts/update.sh`
- Simplified to plain `git pull origin main`
- Removed `reset hard HEAD` step — never touches project directories

### `README.md`
- Updated "Upgrading existing projects" section for the additive model
- Documents the `extensions/` directory pattern
- Migration path for old-model projects

## Files Modified
- `prompts/orchestrate.md` — reordered read precedence, added extension checks
- `prompts/onboarding.md` — removed diff/merge section, simplified setup
- `scripts/update.sh` — simplified to plain git pull
- `README.md` — documented new upgrade model