persist: blob backend — store the ref/CID, never the bytes + 14 tests

blob.sx: a blob ref is {:cid :size :mime}; the blob store is a separate
injected dependency (perform in prod, mock content store in tests).
persist/blob-store puts bytes and returns only the ref; bytes live in a
content-addressed store (artdag/IPFS). Tests assert refs in log/kv never carry
the bytes + content-address dedup. 105/105.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/persist/blob.sx

@@ -0,0 +1,66 @@
+; persist/blob — large objects (images, media) are NOT persist's to hold. They
+; live in a content-addressed store (artdag/IPFS); persist stores only a
+; reference: {:cid :size :mime}. The blob store is a SEPARATE injected
+; dependency with its own transport (perform in production, a mock content store
+; in tests), distinct from the event/kv backend. The invariant: a blob ref that
+; lands in the log or kv carries the CID + metadata and never the bytes.
+; Requires: lib/persist/backend.sx.
+
+(define persist/blob-ref (fn (cid size mime) {:mime mime :size size :cid cid}))
+(define persist/blob-ref? (fn (r) (has-key? r :cid)))
+(define persist/blob-cid (fn (r) (get r :cid)))
+(define persist/blob-size (fn (r) (get r :size)))
+(define persist/blob-mime (fn (r) (get r :mime)))
+
+; blob store protocol over an injectable transport
+(define persist/blob-io (fn (transport) {:put (fn (bytes mime) (transport {:op "blob/put" :args (list bytes mime)})) :get (fn (cid) (transport {:op "blob/get" :args (list cid)})) :has? (fn (cid) (transport {:op "blob/has?" :args (list cid)}))}))
+
+; production blob store — transport is the kernel's perform
+(define
+  persist/blob-store-backend
+  (fn () (persist/blob-io (fn (req) (perform req)))))
+
+; store bytes via the blob backend; return ONLY the ref (cid + metadata) — this
+; is what the caller persists in the log/kv. The bytes never enter persist.
+(define
+  persist/blob-store
+  (fn
+    (blob bytes mime)
+    (let
+      ((cid ((get blob :put) bytes mime)))
+      (persist/blob-ref cid (len bytes) mime))))
+
+(define
+  persist/blob-fetch
+  (fn (blob ref) ((get blob :get) (persist/blob-cid ref))))
+(define
+  persist/blob-exists?
+  (fn (blob ref) ((get blob :has?) (persist/blob-cid ref))))
+
+; mock content-addressed store (stands in for artdag/IPFS). CID is a
+; deterministic content address: identical bytes dedupe to one CID. A real
+; store computes a SHA3/IPFS CID host-side; the prefix keeps the mock readable.
+(define persist/blob-cid-of (fn (bytes) (str "cid:" bytes)))
+
+(define
+  persist/blob-serve
+  (fn
+    (store req)
+    (let
+      ((op (get req :op)) (args (get req :args)))
+      (cond
+        ((equal? op "blob/put")
+          (let
+            ((cid (persist/blob-cid-of (first args))))
+            (begin (persist/backend-kv-put store cid (first args)) cid)))
+        ((equal? op "blob/get") (persist/backend-kv-get store (first args)))
+        ((equal? op "blob/has?")
+          (persist/backend-kv-has? store (first args)))
+        (else (error (str "persist/blob-serve: unknown op " op)))))))
+
+(define
+  persist/blob-mock-transport
+  (fn (store) (fn (req) (persist/blob-serve store req))))
+(define
+  persist/mock-blob
+  (fn (store) (persist/blob-io (persist/blob-mock-transport store))))