fix(migration): emit bunfig.toml with peer = false to unblock bun installs

vitest@4.1.5 declares a `vite^6/^7/^8` peer dep. When the user's project
overrides `vite` to `@voidzero-dev/vite-plus-core` (version 0.0.0 in dev
and 0.1.21 on npm — neither matches), bun aborts with:
  error: vite@^6.0.0 || ^7.0.0 || ^8.0.0 failed to resolve

pnpm/yarn/npm tolerate this redirect; bun does not, and offers no
`peerDependencyRules`-style escape hatch — only `[install] peer = false`
in `bunfig.toml`. vite-plus already provides the vite surface the user
needs, so disabling bun's auto-install of *missing* peers is safe here:
the redirected vite is the only one that ever fails, and other vitest
peers (jsdom, happy-dom, @vitest/*, etc.) are upstream-optional and
either pulled in transitively or user-installed.

`ensureBunfigPeerSuppression` writes/merges `bunfig.toml` whenever the
migrator touches a bun project — both the monorepo path (via
`rewriteBunCatalog`) and the standalone path (in
`rewriteStandaloneProject`'s post-package.json branch). Honors any
pre-existing `peer =` setting so a user who deliberately set `peer = true`
keeps it.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: Brooooooklyn

packages/cli/snap-tests-global/new-vite-monorepo-bun/snap.txt

@@ -3,6 +3,7 @@
 AGENTS.md
 README.md
 apps
+bunfig.toml
 package.json
 packages
 tsconfig.json

packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts

@@ -123,6 +123,64 @@ describe('rewriteMonorepo bun catalog with file: protocol', () => {
     expect(pkg.devDependencies.vite).toBe('file:/tmp/tgz/voidzero-dev-vite-plus-core-0.0.0.tgz');
   });
 
+  it('writes bunfig.toml with `peer = false` so vitest peer-dep on vite does not break install', () => {
+    // vitest@4.1.5 declares peer vite^6/^7/^8. With overrides.vite pointing at
+    // file:vite-plus-core@0.0.0 (whose package.json version does not match),
+    // bun aborts the install. pnpm/yarn/npm tolerate this; bun has no equivalent
+    // to pnpm's peerDependencyRules and only respects the `[install] peer = false`
+    // setting in bunfig.toml. The migrator must emit that file or every bun
+    // user hits `error: vite@^6.0.0 || ^7.0.0 || ^8.0.0 failed to resolve`.
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-monorepo',
+        workspaces: ['packages/*'],
+        packageManager: 'bun@1.3.11',
+      }),
+    );
+    rewriteMonorepo(makeWorkspaceInfo(tmpDir, PackageManager.bun), true);
+
+    const bunfigPath = path.join(tmpDir, 'bunfig.toml');
+    expect(fs.existsSync(bunfigPath)).toBe(true);
+    expect(fs.readFileSync(bunfigPath, 'utf8')).toMatch(/^\[install\][\s\S]*peer\s*=\s*false/m);
+  });
+
+  it('preserves an existing bunfig.toml `peer` setting (does not overwrite user intent)', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-monorepo',
+        workspaces: ['packages/*'],
+        packageManager: 'bun@1.3.11',
+      }),
+    );
+    fs.writeFileSync(path.join(tmpDir, 'bunfig.toml'), '[install]\npeer = true\n');
+    rewriteMonorepo(makeWorkspaceInfo(tmpDir, PackageManager.bun), true);
+
+    // User's explicit `peer = true` should remain — we don't silently flip it.
+    expect(fs.readFileSync(path.join(tmpDir, 'bunfig.toml'), 'utf8')).toMatch(/peer\s*=\s*true/);
+  });
+
+  it('appends `peer = false` under an existing [install] section without `peer` setting', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-monorepo',
+        workspaces: ['packages/*'],
+        packageManager: 'bun@1.3.11',
+      }),
+    );
+    fs.writeFileSync(
+      path.join(tmpDir, 'bunfig.toml'),
+      '[install]\nregistry = "https://registry.npmjs.org/"\n',
+    );
+    rewriteMonorepo(makeWorkspaceInfo(tmpDir, PackageManager.bun), true);
+
+    const bunfig = fs.readFileSync(path.join(tmpDir, 'bunfig.toml'), 'utf8');
+    expect(bunfig).toMatch(/registry\s*=\s*"https:\/\/registry\.npmjs\.org\/"/);
+    expect(bunfig).toMatch(/peer\s*=\s*false/);
+  });
+
   it('does not write file: paths into peer dependencies', () => {
     const pkg = {
       peerDependencies: {

packages/cli/src/migration/migrator.ts

@@ -1005,6 +1005,8 @@ export function rewriteStandaloneProject(
 
   if (packageManager === PackageManager.yarn) {
     rewriteYarnrcYml(projectPath);
+  } else if (packageManager === PackageManager.bun) {
+    ensureBunfigPeerSuppression(projectPath);
   }
 
   // Merge extracted staged config into vite.config.ts, then remove lint-staged from package.json
@@ -1572,6 +1574,42 @@ function rewriteCatalogsObject(catalogs: Record<string, Record<string, string>>)
   }
 }
 
+/**
+ * Bun rejects vitest@4.1.5's `vite^6/^7/^8` peer-dep when the user's project
+ * overrides `vite` to `@voidzero-dev/vite-plus-core` (whose package.json version
+ * does not match those ranges). pnpm/yarn/npm all tolerate this redirect; bun
+ * does not, and there is no `peerDependencyRules`-style escape hatch — only the
+ * `[install] peer = false` setting in `bunfig.toml`.
+ *
+ * `vite-plus`/`@voidzero-dev/vite-plus-core` already provide the vite surface
+ * the user needs, so disabling bun's auto-install of *missing* peers is safe in
+ * this configuration: any vitest peer that's not already pulled in transitively
+ * (jsdom, happy-dom, etc.) is marked optional upstream anyway.
+ *
+ * Writes/merges `bunfig.toml` at `projectPath` so the suppression applies on
+ * the migration's reinstall AND every subsequent `bun install` the user runs.
+ */
+function ensureBunfigPeerSuppression(projectPath: string): void {
+  const bunfigPath = path.join(projectPath, 'bunfig.toml');
+  const block = '[install]\npeer = false\n';
+  if (!fs.existsSync(bunfigPath)) {
+    fs.writeFileSync(bunfigPath, block);
+    return;
+  }
+  const existing = fs.readFileSync(bunfigPath, 'utf8');
+  // Already configured? Leave the user's setting alone — they may have set
+  // `peer = true` deliberately for some other reason and we shouldn't override.
+  if (/^\s*peer\s*=\s*(true|false)\s*$/m.test(existing)) {
+    return;
+  }
+  // Append under existing [install] section, or add a new section.
+  const installSectionRe = /^\[install\][^[]*/m;
+  const next = installSectionRe.test(existing)
+    ? existing.replace(installSectionRe, (section) => `${section.trimEnd()}\npeer = false\n`)
+    : `${existing.trimEnd()}\n\n${block}`;
+  fs.writeFileSync(bunfigPath, next);
+}
+
 /**
  * Write catalog entries to root package.json for bun.
  * Bun stores catalogs in package.json under the `catalog` key,
@@ -1639,6 +1677,8 @@ function rewriteBunCatalog(projectPath: string): void {
 
     return pkg;
   });
+
+  ensureBunfigPeerSuppression(projectPath);
 }
 
 /**