chore: clean up ambiguous root files

.dockerignore

@@ -50,7 +50,6 @@ LICENSE
 DailyLog.md
 Contributing.md
 system_design.md
-FILE Structure
 Metrics.md
 
 # Terraform state (contains sensitive data)

FILE Structure → docs/reference/historical-repository-layout.md

@@ -1,3 +1,10 @@
+# Historical repository layout reference
+
+This manually maintained snapshot was moved from the repository root during the 2026-08-05 root-directory audit. It is retained for historical context only and is **not** a generated current inventory; use the repository tree and service documentation for current paths.
+
+## Original snapshot
+
+```text
 SentinelAI/
 │
 ├── ingestion-service/           # Go - Log ingestion + API gateway
@@ -44,4 +51,5 @@ SentinelAI/
 │   └── streamlit_app.py
 ├── src/
 ├── requirements.txt
-├── README.md
+├── README.md
+```

docs/reference/root-directory-audit.md

@@ -0,0 +1,23 @@
+# Root directory audit
+
+Reviewed on 2026-08-05. This record captures the reference searches and disposition of ambiguous root files.
+
+## Moved
+
+| Original file | Canonical location | Reason |
+| --- | --- | --- |
+| `FILE Structure` | `docs/reference/historical-repository-layout.md` | Unique, manually maintained historical layout reference; moved from a space-containing root filename. |
+| `Prometheus ServiceMonitor (Metrics Credibility)` | `k8s/sentinelai-backend-servicemonitor.yaml` | Unique `ServiceMonitor` manifest; Kubernetes manifests belong under `k8s/`. |
+
+## Removed duplicate
+
+| Removed file | Canonical source | Verification |
+| --- | --- | --- |
+| `Test` | `tests/` directory | The root file was only a five-file snapshot of the existing test tree. Repository searches found no build, CI, Docker, script, documentation, or source reference to the root snapshot. |
+
+## NEEDS HUMAN DECISION
+
+| Filename | Why deletion is uncertain | Recommended action |
+| --- | --- | --- |
+| `bindings.cpp` | It is a unique pybind11 module declaration for `ingestion_cpp`; no `ingestion_cpp/` implementation or build reference was found, so its intended integration cannot be proven. | Identify or add the owning extension build and implementation; then either move it with that component or remove it in a dedicated, build-validated PR. |
+| `drift_engine.cpp` | It is not identical to `drift-engine/drift_engine.cpp`: the root program is a PSI-only sample, while the service implementation parses JSON and computes PSI/KS. `docker/Dockerfile` explicitly compiles the root file. | Choose one supported drift-engine image/build path, update the Docker/build/documentation references, then remove the other implementation only after an image build and behavior test. |