content-addressed blob storage: blob_storage.py, memory, local, and S3 adapters

docs/architecture-blueprint.md

@@ -190,7 +190,7 @@ Required MVP ports:
 
 - Repository port for assets, representations, metadata, relationships,
   versions, runs, audit events, and exports.
-- Object/content store port for source, normalized, and derived content payloads.
+- Blob/content store port for source, normalized, and derived content payloads.
 - Search index port for lexical search and later semantic/hybrid retrieval.
 - Extractor port for format-specific normalization.
 - Connector port for source systems.
@@ -211,6 +211,10 @@ Adapter rules:
   Markitect where useful, but they are not the canonical engine identity or
   storage model. The canonical layer remains asset, representation, metadata,
   lifecycle, policy, lineage, and audit state.
+- Blob storage is infrastructure behind `AssetRepresentation.storage_ref`.
+  Whole-object content addressing, digest verification, and chunked byte
+  streaming belong behind the blob port. Local filesystem and S3 are adapters,
+  not different domain models.
 - `llm-connect` or equivalent is an adapter for LLM providers.
 - `phase-memory` is an adjacent memory runtime; this engine may exchange opaque
   memory references or context packages but should not implement memory phases.
@@ -251,6 +255,9 @@ Recommended storage style:
   adapter-specific payloads.
 - Separate content/object references for large source, normalized, or derived
   payloads.
+- Store blob bytes outside repository rows when content is non-trivial. Keep
+  representation digest, size, media type, kind, producer, and storage ref in
+  the repository, and let blob adapters handle byte persistence and dedupe.
 - Append-only audit events and change records.
 - Deterministic ordering fields for pagination and tests.