docs: brief template, builders never run npm or remove files in the canonical checkout, and every gate runs its own npm ci in its worktree (mos-1575); doc only

docs/plans/BRIEF-TEMPLATE.md

@@ -66,6 +66,14 @@ that prove the claim. Or keep it off refactor, in the seat's scratch, and
 cite its path and sha256 in BUILD.md (mos-1570, after row 265's 22 gzip
 logs).
 
+Builders never run npm or remove files in the canonical checkout
+(`/mnt/storage/src/mosaic-stack`), only in their own worktree. Every gate,
+the builder's and the lead's landing gate, runs its own
+`npm ci --ignore-scripts --no-audit --no-fund` in its worktree root and in
+`packages/webui`, and never links to canonical node_modules (mos-1575,
+after canonical node_modules was found empty at 05:45:15Z 10-24 and row
+327's gate went red on it).
+
 ### Handoffs
 
 Every seat hands off directly (DECISIONS Q210, mos-1221). When the owner