docs: add disk capacity incident runbook (Closes #1287)

docs/ops-fundamentals.md

@@ -23,3 +23,20 @@
 - API contracts + versioning
 - independent deployability
 - observability: metrics, traces, structured logs
+
+# Disk capacity incident
+
+Root filesystem usage at or above 85% is an operations incident.
+
+1. Capture the initial state with `df -h / /var/lib/gitea`.
+2. Inspect directory sizes and active processes before cleanup. Reclaim only
+   disposable caches and abandoned temporary environments. Responders must not
+   delete Gitea data, repositories, databases, secrets, or active release
+   artifacts.
+3. Re-run `df -h / /var/lib/gitea`; usage must be below 85%.
+4. Confirm the release path with `systemctl is-active gitea act_runner`, then run
+   the repository test suite.
+
+Record the before and after usage in the incident ticket. If safe cleanup cannot
+restore capacity below 85%, keep the incident open and escalate storage
+expansion rather than removing durable data.

tests/test_ops_fundamentals.py

@@ -0,0 +1,16 @@
+from pathlib import Path
+
+
+RUNBOOK = Path(__file__).parents[1] / "docs" / "ops-fundamentals.md"
+
+
+def test_disk_capacity_runbook_requires_safe_remediation_and_release_verification():
+    text = " ".join(RUNBOOK.read_text().split())
+
+    assert "Disk capacity incident" in text
+    assert "85%" in text
+    assert "df -h / /var/lib/gitea" in text
+    assert "disposable caches and abandoned temporary environments" in text
+    assert "must not delete Gitea data" in text
+    assert "systemctl is-active gitea act_runner" in text
+    assert "repository test suite" in text