docs: REPORT/README/CONTEXT for v0.58.0 prevention layer (9201 re-provision validated)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

controller/README.md

@@ -149,6 +149,16 @@ The app catalog lives in a separate Git repository. The controller:
    - Hard block if `used_mb + new_request > usable_memory`
    - `CommittedMemory()` (declared sum) still used for soft overcommit warning only
    - Deploy page shows real memory usage bar (not declared reservations)
+4b. **Docker-data volume reserved-buffer gate (v0.58.0, storage-split prevention layer):** the OS rootfs
+   and Docker data are split onto separate volumes; infra (controller/traefik/cloudflared/filebrowser)
+   shares the one Docker data-root (`/var/lib/docker`) and is protected by **prevention, not placement**.
+   `system.GetDockerVolumeHeadroom()` measures the Docker-data volume via `statfs("/")` (the controller
+   container's overlay root is the upperdir on that volume — true with the golden's **overlay2** driver)
+   and reserves `max(5 GB, 10%)`. `deployStack` **refuses a new deploy (HTTP 507)** when free space is
+   at/under the buffer; the deploy page shows the warning + disables the button. Fail-open on a statfs
+   error. The runtime disk monitor (`healthcheck.go`, warn 80% / crit 90%) watches the same volume and
+   trips above the buffer. (Assumes the split guest's large data volume; the golden bakes overlay2 + log
+   rotation so images+volumes live on the data volume, not `/var/lib/containerd`.)
 5. Pre-generated secret values are submitted as hidden form inputs so the **same values** the user saw are saved to `app.yaml` (no silent re-generation on submit). Controller saves `app.yaml`, sets in-memory `Deployed` + `Deploying` flags, then runs `docker compose up -d` **asynchronously** in a goroutine — API returns immediately so the UI switches to the progress panel without waiting for image pulls. On failure the goroutine reverts both disk and in-memory state and sets `DeployError`.
 6. 3-step progress panel polls `GET /api/stacks/{name}` every 3s: config saved → `deploying` (pulling images) → containers starting → health check passed. New `StateDeploying` state shown while compose-up is in progress (no containers yet).
 7. Post-deploy: locked fields (DB_PASSWORD, etc.) become read-only; the "Automatikusan generált értékek" section continues to show the saved values on the settings page