feat(storage): json backend — one human-readable file per unit

Atomic whole-file replacement (same-dir temp + fsync + rename + parent
fsync); the in-memory unit state is authoritative and the file is always
the current net state, pretty-printed. Missing files open as empty units
and materialize on first write; foreign or unparsable files reject with
malformed-medium, stored-version drift with version-mismatch.

packages/storage/storage-json/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "@deepseek-ai/dsh-storage-json",
+  "description": "JSON file KV storage backend for the DeepSeek Harness storage hub",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "main": "lib/index.js",
+  "types": "lib/types/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./lib/types/index.d.ts",
+      "default": "./lib/index.js"
+    },
+    "./invariant": {
+      "types": "./lib/types/invariant.d.ts",
+      "default": "./lib/invariant.js"
+    },
+    "./src/*": "./src/*",
+    "./package.json": "./package.json"
+  },
+  "files": [
+    "lib/index.js",
+    "lib/invariant.js",
+    "lib/types/**/*.d.ts",
+    "lib/types/**/*.d.ts.map",
+    "src"
+  ],
+  "license": "BSD-3-Clause",
+  "peerDependencies": {
+    "@deepseek-ai/dsh-invariants": "^0.0.1",
+    "@deepseek-ai/dsh-storage": "^0.0.1",
+    "cordis": "^4.0.0-rc.7"
+  },
+  "dependencies": {
+    "schemastery": "^3.18.0"
+  },
+  "devDependencies": {
+    "@deepseek-ai/dsh-invariants": "workspace:^",
+    "@deepseek-ai/dsh-storage": "workspace:^",
+    "cordis": "^4.0.0-rc.7"
+  }
+}