ci: enforce 85% pytest coverage threshold in CI

Added pytest-cov to dev dependencies and --cov runcycles --cov-fail-under=85
to the CI test step. Current coverage is 100%. Updated README Development
section to document the coverage command.

https://claude.ai/code/session_01HXikxwPuurjunotYpbmsE7

Author: claude

.github/workflows/ci.yml

@@ -34,5 +34,5 @@ jobs:
       - name: Type check with mypy
         run: mypy runcycles
 
-      - name: Run tests
-        run: pytest
+      - name: Run tests with coverage
+        run: pytest --cov runcycles --cov-fail-under=85

README.md

@@ -312,8 +312,8 @@ ruff check .
 # Type check (strict mode)
 mypy runcycles
 
-# Run tests
-pytest
+# Run tests with coverage (85% threshold enforced in CI)
+pytest --cov runcycles --cov-fail-under=85
 ```
 
 CI runs all three checks on Python 3.10 and 3.12 for every push and pull request.

pyproject.toml

@@ -18,6 +18,7 @@ dependencies = [
 dev = [
     "pytest>=7.0",
     "pytest-asyncio>=0.21",
+    "pytest-cov>=4.0",
     "pytest-httpx>=0.30",
     "mypy>=1.0",
     "ruff>=0.1",