bug(scaffold): template .npmrc overwritten when non-default registry is configured

[Sertug17]

Summary

scaffold renames _npmrc → .npmrc from the template (via copyTemplate), then unconditionally overwrites that .npmrc when a non-default npm registry is detected. Any content the template had in _npmrc is silently lost.

Root Cause

packages/agent-core/src/scaffold.ts:

// Step 1: renames template's _npmrc → .npmrc
copyTemplate(templateDir, targetDir, replacements);

// Step 2: overwrites it entirely
if (sapiomRegistry !== DEFAULT_REGISTRY) {
  writeFileSync(
    path.join(targetDir, ".npmrc"),
    `@sapiom:registry=${sapiomRegistry}\n`, // ❌ template content gone
  );
}

DOTFILE_NAMES explicitly includes "_npmrc", so templates are expected to carry npmrc content. For any developer using a custom/private registry (Verdaccio, private npm), that content is silently dropped.

Fix

Append to the existing file instead of overwriting:

const npmrcPath = path.join(targetDir, ".npmrc");
const existing = existsSync(npmrcPath) ? readFileSync(npmrcPath, "utf8") : "";
const line = `@sapiom:registry=${sapiomRegistry}\n`;
if (!existing.includes(line)) {
  writeFileSync(npmrcPath, existing + line);
}