docs(topdata): define global injection conditions

internal/topdata/CLASS_FEAT_GLOBAL_INJECTS_CONTRACT.md

@@ -65,6 +65,33 @@ effective output while keeping project policy in topdata authoring files.
 `position` defaults to `append`. The module uses `prepend` for class feat
 injections to keep generated policy rows before per-class authored rows.
 
+## Global Injection Grammar
+
+Each injection entry may use only `row`, `require_present`, `any_present`, and
+`unless_present`. `when_present` is invalid and rejected; it is not an alias.
+
+```json
+{
+  "row": {
+    "FeatIndex": { "id": "feat:example" }
+  },
+  "require_present": [{ "field": "FeatIndex", "id": "feat:required" }],
+  "any_present": [
+    { "field": "FeatIndex", "id": "masterfeats:metamagic" },
+    { "field": "FeatIndex", "id": "masterfeats:combat" }
+  ],
+  "unless_present": [{ "field": "FeatIndex", "id": "feat:example" }]
+}
+```
+
+- `require_present` means every listed reference must exist.
+- `any_present` means at least one listed reference must exist, and the array
+  must not be empty.
+- `unless_present` means none of the listed references may exist.
+- Every present group on an entry must pass.
+- Conditions observe the current rows in injection order, so earlier injections
+  can affect later conditions.
+
 ## Acceptance Criteria
 
 - Class feat output contains the same effective shared feats as the prior YAML