Add Fabric graph read model ingest

docs/fabric-graph-read-model.md

@@ -0,0 +1,67 @@
+# Fabric Graph Read Model
+
+State Hub stores Railiance Fabric graph exports as a read model. Fabric remains
+the source of truth; the State Hub tables are cache/index/query state for
+dashboard and operator use.
+
+## Refresh After Fabric Reset/Reingest
+
+Start or confirm the Railiance Fabric registry is serving its export:
+
+```bash
+curl -s http://127.0.0.1:8765/exports/state-hub
+```
+
+Pull the current export into State Hub:
+
+```bash
+curl -s -X POST http://127.0.0.1:8000/fabric/graph-exports/pull \
+  -H "Content-Type: application/json" \
+  -d '{
+    "source_repo_slug": "railiance-fabric",
+    "source_url": "http://127.0.0.1:8765/exports/state-hub",
+    "requested_by": "operator"
+  }'
+```
+
+For a saved export file, post the FabricGraphExport JSON directly:
+
+```bash
+curl -s -X POST "http://127.0.0.1:8000/fabric/graph-exports?source_repo_slug=railiance-fabric" \
+  -H "Content-Type: application/json" \
+  --data-binary @fabric-state-hub-export.json
+```
+
+## Query Checks
+
+Latest import and counts:
+
+```bash
+curl -s http://127.0.0.1:8000/fabric/graph-exports/latest
+curl -s http://127.0.0.1:8000/fabric/graph/summary
+```
+
+Representative relationship queries:
+
+```bash
+curl -s "http://127.0.0.1:8000/fabric/graph/edges?canonical_relationship=exposes"
+curl -s "http://127.0.0.1:8000/fabric/graph/edges?canonical_relationship=depends_on"
+curl -s "http://127.0.0.1:8000/fabric/graph/edges?canonical_relationship=implements"
+```
+
+Node filters:
+
+```bash
+curl -s "http://127.0.0.1:8000/fabric/graph/nodes?repo=state-hub"
+curl -s "http://127.0.0.1:8000/fabric/graph/nodes?domain=custodian"
+curl -s "http://127.0.0.1:8000/fabric/graph/nodes?canonical_category=service"
+```
+
+## Guarantees
+
+- malformed exports create a failed import/progress record but do not write
+  graph node or edge rows
+- repeated imports of the same graph content are idempotent
+- latest selection is per `source_repo_slug`
+- read endpoints do not mutate workstreams, tasks, messages, decisions, or
+  progress rows