BG7, BN7: a fetch naming builds reads each package member from the artifact store

Each member's build is read at /v2/<module>/<artifact>/blobs/<digest> through the required provision artifact-store
(bound to a file), checked against its digest and laid as the package it names: a Go module zip replaced in the temporary
modfile, an npm tarball in node_modules. A mismatch or a store that does not answer fails the step naming the member.

Builds: design 47 G §465, §373, §466 (lead answer A-151)

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-build-node/module.json

@@ -66,12 +66,14 @@
   ],
   "requires": [
     {"name": "detected-steps", "storage": "key-value", "template": "state", "options": {"history": 1}},
+    "artifact-store",
     "forge-account",
     "npm-package-registry",
     "node-toolchain",
     "node-tools"
   ],
   "binds": {
+    "artifact-store": "${dir:state}/artifact-store.json",
     "npm-package-registry": "${dir:state}/package-registry.json"
   },
   "invokes": [