chore: add mission infrastructure for execution loop validation system

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

.factory/library/user-testing.md

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+# User Testing
+
+Testing surface, required testing skills/tools, and resource cost classification.
+
+## Validation Surface
+
+| Surface | Description | Tool |
+|---------|-------------|------|
+| Dashboard UI | Mission manager with assertions panel, loop states, validation controls | agent-browser |
+| REST API | Assertion CRUD, validation trigger, loop state, runs, recovery | curl |
+| CLI | Mission commands | Manual verification |
+
+## Validation Concurrency
+
+**Machine specs:** 28 CPU cores, 256 GB RAM
+
+**agent-browser (lightweight app):**
+- Dashboard is a lightweight web app (~200 MB with dev server)
+- Each agent-browser instance: ~300 MB RAM
+- Dev server: ~200 MB
+- Usable headroom: 256 GB * 0.7 = ~179 GB (very generous)
+- Max concurrent validators: **5** (standard max)
+
+## Resource Cost Notes
+
+- Dashboard dev server (`fn dashboard`) needs to be running for browser tests
+- API tests via curl are very lightweight — no concurrency limit needed
+- Tests should use a fresh `.fusion/fusion.db` to avoid state pollution