fix: deleting READNE.md during upgrade

Author: bhdicaire

docs/adr/0004-detach-and-upgrade-product-files.md

@@ -16,15 +16,17 @@ product README with `docs/README.md`, an operator-focused instance README, then
 instance.
 
 `npm run upgrade` refreshes product-owned paths from upstream while protecting instance-owned paths such as `custom/`,
-`wrangler.toml`, and `.dev.vars`.
+`wrangler.toml`, `.dev.vars`, and `README.md`.
 
 The default upgrade path includes product files such as `defaults/`, `scripts/`, `package.json`, `package-lock.json`,
-`README.md`, and `LICENSE`.
+and `LICENSE`. It does not refresh `README.md`, because `npm run detach` replaces the upstream README with the
+operator-focused instance README.
 
 ## Consequences
 
 - New instances can start as independent repositories
 - Detached instances get an operator-focused README at the repository root
 - Upgrades can refresh product behavior without overwriting local configuration
+- Upgrades do not reintroduce the upstream product README into detached instances
 - Protected local paths remain the operator's responsibility
 - Release metadata and upstream workflow files do not leak into detached instances

scripts/upgrade.mjs

@@ -8,8 +8,8 @@ import { execFileSync, spawnSync } from "node:child_process";
 const ROOT = process.cwd();
 const DEFAULT_REMOTE = "https://github.com/vanityURLs/code.git";
 const DEFAULT_REF = "main";
-const DEFAULT_PATHS = ["defaults", "scripts", "package.json", "package-lock.json", "README.md", "LICENSE"];
-const PROTECTED_PATHS = ["custom", "wrangler.toml", ".dev.vars"];
+const DEFAULT_PATHS = ["defaults", "scripts", "package.json", "package-lock.json", "LICENSE"];
+const PROTECTED_PATHS = ["custom", "wrangler.toml", ".dev.vars", "README.md"];
 
 function parseArgs(argv) {
   const args = {