chore: add quality infra matrix, constraints, and test baseline fixes

docs/dependency-locking.md

@@ -0,0 +1,30 @@
+# Dependency Locking Guide
+
+Agent Reach uses `constraints.txt` as a reproducible dependency baseline.
+
+## Why
+
+- Keep local/CI dependency graph stable
+- Reduce "works on my machine" drift
+- Make regression results easier to compare
+
+## Install with constraints
+
+```bash
+pip install -c constraints.txt -e .[dev]
+```
+
+## Update workflow
+
+1. Update `pyproject.toml` dependency ranges as needed.
+2. Validate against latest compatible versions locally.
+3. Update pinned versions in `constraints.txt`.
+4. Run validation:
+
+```bash
+pytest -q
+ruff check agent_reach tests
+mypy agent_reach
+```
+
+5. Open PR with dependency and validation notes.