Split memory contract modules

Author: nshkrdotcom

.blitz/test_state_v1/indexes/task_states.ndjson

@@ -7,6 +7,11 @@ context-budget decisions.
 The package is pattern-engine-free and carries refs, hashes, bounded excerpts, and
 policy names only. Raw memory bodies are rejected at construction boundaries.
 
+`OuterBrain.MemoryContracts` is the stable public facade. Individual
+contracts live in focused modules under `OuterBrain.MemoryContracts` for
+identity refs, evidence refs, redaction/access policy, context-budget facts,
+write/query intents, shared vocabularies, and boundary validation.
+
 ## Persistence Documentation
 
 See `docs/persistence.md` for tiers, defaults, adapters, unsupported selections, config examples, restart claims, durability claims, debug sidecar behavior, redaction guarantees, migration or preflight behavior, and no-bypass scope when applicable.