feat: expose bounded organization hierarchy routing

docs/ORGANIZATION_MODEL.md

@@ -66,6 +66,36 @@ The close-out condition is that Access role resolution works with canonical
 Organizations plus IDM installed and still works through projection fallback
 for transition deployments.
 
+## Directory Contracts
+
+`organizations.directory` remains the small compatibility contract for direct
+unit and function lookup. It deliberately retains the legacy `parent_id`
+projection needed by existing Access and IDM integrations.
+
+`organizations.hierarchyDirectory` is the structure-aware contract for new
+consumers. It provides:
+
+- tenant-scoped unit-type and function-type references;
+- function resolution by type and an explicit set of units;
+- unit resolution by type, optionally bounded to one named structure;
+- batched ancestor, descendant, and path resolution with a required structure,
+  optional relation-type filter, and bounded depth;
+- the exact structure, relation type, and relation edge for every path step;
+- explicit missing, inactive, unreachable, invalid-filter, cycle, and
+  depth-limit state.
+
+An edge is traversed from `source_unit_id` to `target_unit_id` for descendant
+lookups and in reverse for ancestor lookups. Consumers must select a structure;
+the provider never treats `parent_id` or one arbitrary structure as the
+institution's universal hierarchy.
+
+Committed changes emit versioned `organizations.<resource>.<action>.v1`
+platform events for units, functions, their types, structures, relation types,
+and relation edges. The event payload contains schema version `1`, tenant and
+resource references, status, changed fields, and routing-relevant IDs so
+directory consumers can invalidate derived addresses without importing this
+module's models.
+
 ## UI Boundary
 
 The organization workspace at `/organizations` is the primary module UI for