sx-git Phase 1: blob/tree/commit/tag as content-addressed typed objects (TDD)

Objects are plain dicts over persist kv, addressed by sx1:<sha256> of the
artdag/canon canonical form (sorted dict keys) — native CIDs, extensible
fields participate in identity. 38/38.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/git/object.sx

@@ -0,0 +1,81 @@
+; lib/git/object.sx — sx-git Phase 1: blob/tree/commit/tag as content-addressed
+; TYPED objects over the persist kv store. Identity = host digest of the
+; canonical serialization (artdag/canon: sorted dict keys, escaped strings) —
+; native CIDs, NOT git wire bytes. Objects are plain dicts: typed, extensible;
+; unknown fields round-trip and participate in the CID.
+; Requires: lib/persist/backend.sx, lib/persist/kv.sx, lib/artdag/dag.sx.
+
+; ---- canonical form + content id ----
+(define git/canon (fn (obj) (artdag/canon obj)))
+
+(define
+  git/cid
+  (fn (obj) (str "sx1:" (crypto-sha256 (artdag/canon obj)))))
+
+; ---- repo handle: a persist backend + key prefix (many repos per db) ----
+(define git/repo-named (fn (db name) {:prefix name :db db}))
+(define git/repo (fn (db) (git/repo-named db "git")))
+(define git/repo-db (fn (repo) (get repo :db)))
+(define git/obj-key (fn (repo cid) (str (get repo :prefix) "/obj/" cid)))
+
+; ---- constructors ----
+(define git/blob (fn (data) {:data data :type "blob"}))
+
+; entries: dict of name -> entry, entry = {:kind "blob"|"tree" :cid cid ...}
+(define git/tree (fn (entries) {:type "tree" :entries entries}))
+(define git/tree-entry (fn (kind cid) {:kind kind :cid cid}))
+
+; meta: open dict (:author :message :time ... anything); protected keys win
+(define git/commit (fn (tree parents meta) (merge meta {:type "commit" :tree tree :parents parents})))
+
+(define git/tag (fn (target name meta) (merge meta {:name name :type "tag" :target target})))
+
+; ---- predicates / accessors ----
+(define git/object-type (fn (obj) (get obj :type)))
+(define
+  git/blob?
+  (fn (obj) (and (dict? obj) (equal? (get obj :type) "blob"))))
+(define
+  git/tree?
+  (fn (obj) (and (dict? obj) (equal? (get obj :type) "tree"))))
+(define
+  git/commit?
+  (fn (obj) (and (dict? obj) (equal? (get obj :type) "commit"))))
+(define
+  git/tag?
+  (fn (obj) (and (dict? obj) (equal? (get obj :type) "tag"))))
+
+(define git/blob-data (fn (obj) (get obj :data)))
+(define git/tree-entries (fn (obj) (get obj :entries)))
+(define git/tree-entry-for (fn (obj name) (get (get obj :entries) name)))
+(define
+  git/tree-names
+  (fn (obj) (artdag/sort-strings (keys (get obj :entries)))))
+(define git/entry-cid (fn (entry) (get entry :cid)))
+(define git/entry-kind (fn (entry) (get entry :kind)))
+(define git/commit-tree (fn (obj) (get obj :tree)))
+(define git/commit-parents (fn (obj) (get obj :parents)))
+(define git/commit-author (fn (obj) (get obj :author)))
+(define git/commit-message (fn (obj) (get obj :message)))
+(define git/tag-target (fn (obj) (get obj :target)))
+(define git/tag-name (fn (obj) (get obj :name)))
+
+; ---- object store: write/read/has, keyed by cid ----
+(define
+  git/write
+  (fn
+    (repo obj)
+    (let
+      ((cid (git/cid obj)))
+      (begin (persist/kv-put (get repo :db) (git/obj-key repo cid) obj) cid))))
+
+(define
+  git/read
+  (fn (repo cid) (persist/kv-get (get repo :db) (git/obj-key repo cid))))
+
+(define
+  git/has?
+  (fn (repo cid) (persist/kv-has? (get repo :db) (git/obj-key repo cid))))
+
+; convenience: write a blob straight from data
+(define git/write-blob (fn (repo data) (git/write repo (git/blob data))))