Tune graph layout affinities

docs/graph-explorer-contract.md

@@ -89,6 +89,14 @@ Hosts should also include useful optional fields when available: `label`,
 `freshnessState`, `confidence`, `visualSize`, `ownership`, `unresolved`,
 `sourceReferences`, and `deepLinks`.
 
+Edges may include layout hints used by the client-side layout engine:
+`sameRepo`, `sourceRepo`, `targetRepo`, `layoutAffinity`,
+`layoutIdealLength`, and `layoutElasticity`. Fabric uses these hints to keep
+same-repo entities closer than cross-repo dependencies. Deployment-to-server
+edges are intentionally shortest and most elastic; deployment-to-repo edges are
+longer and looser so infrastructure placement does not collapse into the repo
+node.
+
 ## Display State Ownership
 
 The contract allows either the host service or the engine to evaluate display
@@ -115,6 +123,8 @@ The first Fabric manifest declares:
 | Layer | Purpose |
 |-------|---------|
 | `repository` | Registered source repositories, including registered-only repos. |
+| `server` | Endpoint hosts inferred from registered interface URLs. |
+| `deployment` | Service deployment instances per declared environment. |
 | `service` | Service declarations. |
 | `capability` | Capability declarations. |
 | `interface` | Interface declarations. |