diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/package.json b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/package.json
new file mode 100644
index 0000000000..1c7eb23643
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/package.json
@@ -0,0 +1,14 @@
+{
+  "name": "migration-bun-old-no-top-level-catalog",
+  "workspaces": [],
+  "devDependencies": {
+    "vite": "^7.0.0"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "1.2.20",
+      "onFail": "download"
+    }
+  }
+}
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots.toml b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots.toml
new file mode 100644
index 0000000000..74b868c39e
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots.toml
@@ -0,0 +1,9 @@
+[[case]]
+name = "migration_bun_old_no_top_level_catalog"
+vp = "global"
+comment = "Bun before 1.2.21 reads only `workspaces.catalog`, so a top-level `catalog` would fail to resolve."
+steps = [
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "an empty-workspaces bun 1.2.20 project without Vite+ migrates", continue-on-failure = true },
+  { argv = ["vpt", "print-file", "package.json"], comment = "toolchain specs stay concrete and no top-level catalog is written", continue-on-failure = true },
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a second run converges to the already-migrated fast exit", continue-on-failure = true },
+]
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots/migration_bun_old_no_top_level_catalog.md b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots/migration_bun_old_no_top_level_catalog.md
new file mode 100644
index 0000000000..80c62fabd4
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_bun_old_no_top_level_catalog/snapshots/migration_bun_old_no_top_level_catalog.md
@@ -0,0 +1,53 @@
+# migration_bun_old_no_top_level_catalog
+
+Bun before 1.2.21 reads only `workspaces.catalog`, so a top-level `catalog` would fail to resolve.
+
+## `vp migrate --no-interactive`
+
+an empty-workspaces bun 1.2.20 project without Vite+ migrates
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+◇ Migrated . to Vite+ <version>
+• Node <version>  bun <version>
+• 2 config updates applied
+```
+
+## `vpt print-file package.json`
+
+toolchain specs stay concrete and no top-level catalog is written
+
+```
+{
+  "name": "migration-bun-old-no-top-level-catalog",
+  "workspaces": [],
+  "devDependencies": {
+    "vite": "npm:@voidzero-dev/vite-plus-core@<version>",
+    "vite-plus": "<version>"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "<version>",
+      "onFail": "download"
+    }
+  },
+  "overrides": {
+    "vite": "npm:@voidzero-dev/vite-plus-core@<version>"
+  },
+  "scripts": {
+    "prepare": "vp config"
+  }
+}
+```
+
+## `vp migrate --no-interactive`
+
+a second run converges to the already-migrated fast exit
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+This project is already using Vite+! Happy coding!
+```
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/package.json b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/package.json
new file mode 100644
index 0000000000..f1a77611c5
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/package.json
@@ -0,0 +1,25 @@
+{
+  "name": "migration-upgrade-bun-empty-workspaces-catalog",
+  "devDependencies": {
+    "vite-plus": "catalog:",
+    "vitest": "catalog:"
+  },
+  "overrides": {
+    "vite": "catalog:",
+    "vitest": "catalog:"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "1.4.0",
+      "onFail": "download"
+    }
+  },
+  "workspaces": {
+    "packages": [],
+    "catalog": {
+      "vite-plus": "^0.1.20",
+      "vitest": "4.1.9"
+    }
+  }
+}
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots.toml b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots.toml
new file mode 100644
index 0000000000..d556a54dea
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots.toml
@@ -0,0 +1,9 @@
+[[case]]
+name = "migration_upgrade_bun_empty_workspaces_catalog"
+vp = "global"
+comment = "Bun resolves catalogs whenever the root package.json has a `workspaces` field, even with an empty package list (#3375)."
+steps = [
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a single-package bun project with an empty workspaces.packages keeps its catalog", continue-on-failure = true },
+  { argv = ["vpt", "print-file", "package.json"], comment = "toolchain specs stay catalog: and the workspaces.catalog is rewritten in place", continue-on-failure = true },
+  { argv = ["vp", "migrate", "--no-interactive"], comment = "a second run converges to the already-migrated fast exit", continue-on-failure = true },
+]
diff --git a/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots/migration_upgrade_bun_empty_workspaces_catalog.md b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots/migration_upgrade_bun_empty_workspaces_catalog.md
new file mode 100644
index 0000000000..539c32d97a
--- /dev/null
+++ b/crates/vp_cli_snapshots/tests/cli_snapshots/fixtures/migration_upgrade_bun_empty_workspaces_catalog/snapshots/migration_upgrade_bun_empty_workspaces_catalog.md
@@ -0,0 +1,59 @@
+# migration_upgrade_bun_empty_workspaces_catalog
+
+Bun resolves catalogs whenever the root package.json has a `workspaces` field, even with an empty package list (#3375).
+
+## `vp migrate --no-interactive`
+
+a single-package bun project with an empty workspaces.packages keeps its catalog
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+◇ Updated . to Vite+ <version>
+• Node <version>  bun <version>
+• Dependencies:
+    vite-plus  0.1.20 → <version>
+    vite              → <version>
+• Package manager settings configured
+```
+
+## `vpt print-file package.json`
+
+toolchain specs stay catalog: and the workspaces.catalog is rewritten in place
+
+```
+{
+  "name": "migration-upgrade-bun-empty-workspaces-catalog",
+  "devDependencies": {
+    "vite": "catalog:",
+    "vite-plus": "catalog:"
+  },
+  "overrides": {
+    "vite": "catalog:"
+  },
+  "devEngines": {
+    "packageManager": {
+      "name": "bun",
+      "version": "<version>",
+      "onFail": "download"
+    }
+  },
+  "workspaces": {
+    "packages": [],
+    "catalog": {
+      "vite-plus": "<version>",
+      "vite": "npm:@voidzero-dev/vite-plus-core@<version>"
+    }
+  }
+}
+```
+
+## `vp migrate --no-interactive`
+
+a second run converges to the already-migrated fast exit
+
+```
+VITE+ - The Unified Toolchain for the Web
+
+This project is already using Vite+! Happy coding!
+```
diff --git a/docs/guide/migrate-rules.md b/docs/guide/migrate-rules.md
index c37dcf3c13..3101d3f5dd 100644
--- a/docs/guide/migrate-rules.md
+++ b/docs/guide/migrate-rules.md
@@ -398,7 +398,9 @@ Migration converts the Volta `volta.node` pin to `.node-version`, because Vite+
 
 ### Bun
 
-- Bun catalogs only resolve inside a workspace (a root `package.json` with a non-empty `workspaces`). In a bun workspace, existing top-level or workspace catalog locations and named catalog references are preserved. A standalone (single-package) bun project keeps concrete specs and gets no catalog field, because `bun install` cannot resolve `catalog:` outside a workspace.
+- Bun catalogs only resolve inside a workspace, which is a root `package.json` with a `workspaces` field. An empty `workspaces` field also counts. In a bun workspace, existing top-level or workspace catalog locations and named catalog references are preserved. A standalone bun project without `workspaces` keeps concrete specs and gets no catalog field, because `bun install` cannot resolve `catalog:` outside a workspace.
+- Bun before 1.2.21 reads only catalogs under `workspaces`. On those versions, migration uses catalogs only when the project already has one under `workspaces`, and keeps concrete specs otherwise.
+- When an existing named catalog already owns `vite-plus`, `vite`, or `vitest`, migration adds missing toolchain entries to that catalog instead of creating a default catalog beside it.
 - The core alias is mirrored as a direct `vite` dependency so Bun sees the peer provider before applying overrides.
 
 ## After the Migration
diff --git a/packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts b/packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts
index 93cd6eae33..911be9f99f 100644
--- a/packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts
+++ b/packages/cli/src/migration/__tests__/bun-catalog-file-protocol.spec.ts
@@ -114,8 +114,8 @@ describe('rewriteMonorepo bun catalog with file: protocol', () => {
       overrides: Record<string, string>;
       devDependencies: Record<string, string>;
     };
-    expect(pkg.workspaces.catalog.vite).toBeUndefined();
-    expect(pkg.workspaces.catalog.vitest).toBeUndefined();
+    expect(pkg.workspaces.catalog?.vite).toBeUndefined();
+    expect(pkg.workspaces.catalog?.vitest).toBeUndefined();
     expect(pkg.workspaces.catalogs.build.vite).toBe('^7.0.0');
     expect(pkg.workspaces.catalogs.build.vitest).toBe('^4.0.0');
     expect(pkg.workspaces.catalogs.build.tsdown).toBeUndefined();
diff --git a/packages/cli/src/migration/__tests__/migrator.spec.ts b/packages/cli/src/migration/__tests__/migrator.spec.ts
index c1bcb66131..8b19a86b3a 100644
--- a/packages/cli/src/migration/__tests__/migrator.spec.ts
+++ b/packages/cli/src/migration/__tests__/migrator.spec.ts
@@ -2048,7 +2048,7 @@ describe('ensureVitePlusBootstrap', () => {
     // Regression for the OneSignal-Website-SDK upgrade: a standalone
     // (non-workspace) bun project already on Vite+ with concrete specs. Bun
     // resolves `catalog:` references ONLY inside a workspace (a root
-    // package.json with a non-empty `workspaces`), so converting these edges to
+    // package.json with a `workspaces` field), so converting these edges to
     // `catalog:` and writing a top-level `catalog` field makes `bun install`
     // abort with "vite@catalog: failed to resolve". The upgrade path must keep
     // every managed spec concrete and write NO catalog field, mirroring the
@@ -2106,6 +2106,151 @@ describe('ensureVitePlusBootstrap', () => {
     expect(detectVitePlusBootstrapPending(tmpDir, PackageManager.bun)).toBe(false);
   });
 
+  it('keeps `catalog:` specs in a bun project whose `workspaces.packages` is empty (#3375)', () => {
+    // Bun resolves catalogs whenever the root has a `workspaces` field, even an
+    // empty one, so a single-package project may keep its toolchain there. A
+    // `workspaces.catalog` resolves on every catalog-capable bun, including 1.2.14.
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-root-catalog',
+        devDependencies: { vite: 'catalog:', 'vite-plus': 'catalog:' },
+        overrides: { vite: 'catalog:' },
+        workspaces: {
+          packages: [],
+          catalog: { vite: VITE_PLUS_OVERRIDE_PACKAGES.vite, 'vite-plus': 'latest' },
+        },
+        devEngines: {
+          packageManager: { name: 'bun', version: '1.2.14', onFail: 'download' },
+        },
+      }),
+    );
+
+    expect(detectVitePlusBootstrapPending(tmpDir, PackageManager.bun)).toBe(false);
+    ensureVitePlusBootstrap(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.2.14'));
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      devDependencies: Record<string, string>;
+      overrides: Record<string, string>;
+    };
+    expect(pkg.devDependencies).toEqual({ vite: 'catalog:', 'vite-plus': 'catalog:' });
+    expect(pkg.overrides).toEqual({ vite: 'catalog:' });
+  });
+
+  it('adds a missing @vitest/* entry to the bun catalog it now references', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-coverage',
+        devDependencies: {
+          '@vitest/coverage-v8': '4.1.9',
+          vite: 'catalog:',
+          'vite-plus': 'catalog:',
+        },
+        overrides: { vite: 'catalog:' },
+        workspaces: {
+          packages: [],
+          catalog: { vite: VITE_PLUS_OVERRIDE_PACKAGES.vite, 'vite-plus': '0.1.20' },
+        },
+      }),
+    );
+
+    ensureVitePlusBootstrap(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.4.4'));
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      devDependencies: Record<string, string>;
+      workspaces: { catalog: Record<string, string> };
+    };
+    expect(pkg.devDependencies['@vitest/coverage-v8']).toBe('catalog:');
+    expect(pkg.workspaces.catalog['@vitest/coverage-v8']).toBe(VITEST_VERSION);
+  });
+
+  it('adds vite-plus to the named bun catalog its new reference points at', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-named-catalog',
+        devDependencies: { vite: 'catalog:build', 'vite-plus': '^0.1.20' },
+        overrides: { vite: 'catalog:build' },
+        workspaces: {
+          packages: [],
+          catalogs: { build: { vite: VITE_PLUS_OVERRIDE_PACKAGES.vite } },
+        },
+      }),
+    );
+
+    ensureVitePlusBootstrap(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.4.4'));
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      devDependencies: Record<string, string>;
+      workspaces: {
+        catalog?: Record<string, string>;
+        catalogs: Record<string, Record<string, string>>;
+      };
+    };
+    expect(pkg.devDependencies['vite-plus']).toBe('catalog:build');
+    expect(pkg.workspaces.catalogs.build['vite-plus']).toBe('latest');
+    expect(pkg.workspaces.catalog).toBeUndefined();
+  });
+
+  it('reports a stale bun catalog vite-plus value as pending', () => {
+    // The `catalog:` spec itself looks current, so only the catalog value shows
+    // that vite-plus still needs the upgrade.
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-stale-catalog',
+        devDependencies: { vite: 'catalog:', 'vite-plus': 'catalog:' },
+        overrides: { vite: 'catalog:' },
+        workspaces: {
+          packages: [],
+          catalog: { vite: VITE_PLUS_OVERRIDE_PACKAGES.vite, 'vite-plus': '0.1.20' },
+        },
+        devEngines: {
+          packageManager: { name: 'bun', version: '1.4.4', onFail: 'download' },
+        },
+      }),
+    );
+
+    expect(detectVitePlusBootstrapPending(tmpDir, PackageManager.bun)).toBe(true);
+    ensureVitePlusBootstrap(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.4.4'));
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      workspaces: { catalog: Record<string, string> };
+    };
+    expect(pkg.workspaces.catalog['vite-plus']).not.toBe('0.1.20');
+    expect(detectVitePlusBootstrapPending(tmpDir, PackageManager.bun)).toBe(false);
+  });
+
+  it('keeps concrete specs on bun < 1.2.21, which ignores a top-level catalog', () => {
+    // Without an existing `workspaces.catalog`, rewriteBunCatalog would write a
+    // top-level `catalog`, which bun 1.2.14 to 1.2.20 cannot resolve.
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'old-bun',
+        workspaces: [],
+        devDependencies: { vite: VITE_PLUS_OVERRIDE_PACKAGES.vite, 'vite-plus': 'latest' },
+        devEngines: {
+          packageManager: { name: 'bun', version: '1.2.20', onFail: 'download' },
+        },
+      }),
+    );
+
+    ensureVitePlusBootstrap(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.2.20'));
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      devDependencies: Record<string, string>;
+      catalog?: Record<string, string>;
+    };
+    expect(pkg.devDependencies).toEqual({
+      vite: VITE_PLUS_OVERRIDE_PACKAGES.vite,
+      'vite-plus': 'latest',
+    });
+    expect(pkg.catalog).toBeUndefined();
+    expect(detectVitePlusBootstrapPending(tmpDir, PackageManager.bun)).toBe(false);
+  });
+
   it('rewrites a STANDALONE bun `catalog:` override to the concrete core alias (catalogs unsupported)', () => {
     // Regression: a standalone (non-workspace) bun project already on Vite+ that
     // carries `overrides.vite: "catalog:"` plus a matching top-level `catalog`.
@@ -7961,6 +8106,29 @@ describe('rewriteMonorepo bun catalog', () => {
     expect(overrides.vite).toBe('catalog:');
   });
 
+  it('keeps concrete specs and writes no top-level catalog on bun < 1.2.21', () => {
+    fs.writeFileSync(
+      path.join(tmpDir, 'package.json'),
+      JSON.stringify({
+        name: 'bun-monorepo',
+        workspaces: [],
+        devDependencies: { vite: '^7.0.0' },
+        packageManager: 'bun@1.2.20',
+      }),
+    );
+    rewriteMonorepo(makeWorkspaceInfo(tmpDir, PackageManager.bun, '1.2.20'), true);
+
+    const pkg = readJson(path.join(tmpDir, 'package.json')) as {
+      devDependencies: Record<string, string>;
+      overrides: Record<string, string>;
+      catalog?: Record<string, string>;
+    };
+    expect(pkg.catalog).toBeUndefined();
+    expect(pkg.devDependencies.vite).toBe(VITE_PLUS_OVERRIDE_PACKAGES.vite);
+    expect(pkg.devDependencies['vite-plus']).toBe('latest');
+    expect(pkg.overrides.vite).toBe(VITE_PLUS_OVERRIDE_PACKAGES.vite);
+  });
+
   it('writes catalog to workspaces.catalog when workspaces is an object with existing catalog', () => {
     fs.writeFileSync(
       path.join(tmpDir, 'package.json'),
@@ -8075,8 +8243,11 @@ describe('rewriteMonorepo bun catalog', () => {
       devDependencies: Record<string, string>;
       peerDependencies: Record<string, string>;
     };
-    expect(pkg.catalog.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
+    // Like pnpm, the managed `build` catalog takes the Vite+ entries, so no
+    // default catalog is created beside it.
+    expect(pkg.catalog).toBeUndefined();
     expect(pkg.catalogs.build.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
+    expect(pkg.catalogs.build['vite-plus']).toBe('latest');
     expect(pkg.catalogs.build.react).toBe('^19.0.0');
     expect(pkg.catalogs.build.tsdown).toBeUndefined();
     // Common case (no @vitest/* dep, no vitest source): `vitest` is not managed,
@@ -8086,11 +8257,12 @@ describe('rewriteMonorepo bun catalog', () => {
     expect(pkg.overrides.vite).toBe('catalog:build');
     expect(pkg.overrides.vitest).toBeUndefined();
     expect(pkg.devDependencies.vite).toBe('catalog:build');
+    expect(pkg.devDependencies['vite-plus']).toBe('catalog:build');
     expect(pkg.peerDependencies.vite).toBe('^7.0.0');
     expect(pkg.peerDependencies.vitest).toBe('^4.0.0');
   });
 
-  it('rewrites workspaces named catalogs and writes default catalog beside them', () => {
+  it('rewrites workspaces named catalogs and adds Vite+ entries to the managed one', () => {
     fs.writeFileSync(
       path.join(tmpDir, 'package.json'),
       JSON.stringify({
@@ -8118,15 +8290,15 @@ describe('rewriteMonorepo bun catalog', () => {
       overrides: Record<string, string>;
     };
     expect(pkg.catalog).toBeUndefined();
-    expect(pkg.workspaces.catalog.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
-    expect(pkg.workspaces.catalog['vite-plus']).toBe('latest');
+    expect(pkg.workspaces.catalog).toBeUndefined();
     expect(pkg.workspaces.catalogs.build.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
+    expect(pkg.workspaces.catalogs.build['vite-plus']).toBe('latest');
     expect(pkg.workspaces.catalogs.build.oxlint).toBeUndefined();
     // Common case (no @vitest/* dep, no vitest source): `vitest` is not managed,
     // so the pre-existing named-catalog `vitest` entry is REMOVED.
     expect(pkg.workspaces.catalogs.test.vitest).toBeUndefined();
     expect(pkg.workspaces.catalogs.test.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
-    expect(pkg.overrides.vite).toBe('catalog:');
+    expect(pkg.overrides.vite).toBe('catalog:build');
   });
 
   it('keeps an existing top-level default catalog when workspaces named catalogs exist', () => {
@@ -8155,10 +8327,10 @@ describe('rewriteMonorepo bun catalog', () => {
         catalogs: Record<string, Record<string, string>>;
       };
     };
-    expect(pkg.catalog.react).toBe('^19.0.0');
-    expect(pkg.catalog.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
+    expect(pkg.catalog).toEqual({ react: '^19.0.0' });
     expect(pkg.workspaces.catalog).toBeUndefined();
     expect(pkg.workspaces.catalogs.build.vite).toBe('npm:@voidzero-dev/vite-plus-core@latest');
+    expect(pkg.workspaces.catalogs.build['vite-plus']).toBe('latest');
   });
 });
 
diff --git a/packages/cli/src/migration/migrator/catalog.ts b/packages/cli/src/migration/migrator/catalog.ts
index cd6b13e998..6a94b4dd9a 100644
--- a/packages/cli/src/migration/migrator/catalog.ts
+++ b/packages/cli/src/migration/migrator/catalog.ts
@@ -124,6 +124,33 @@ export function yarnSupportsCatalog(version: string): boolean {
   return versionAtLeast(version, YARN_CATALOG_MIN_VERSION, ['latest', 'next', 'stable']);
 }
 
+const BUN_TOP_LEVEL_CATALOG_MIN_VERSION = '1.2.21';
+
+// Bun resolves `catalog:` references ONLY inside a workspace: a root
+// package.json with a `workspaces` field. An empty one (`[]` or
+// `{ packages: [] }`) is enough (#3375). Bun before 1.2.21 also ignores a
+// top-level `catalog` or `catalogs` (verified on 1.2.14 to 1.2.20), so it
+// needs the nested location that `rewriteBunCatalog` keeps in place. Otherwise
+// `catalog:` edges make `bun install` abort with "vite@catalog: failed to
+// resolve", so the toolchain edges must stay concrete.
+export function bunSupportsCatalog(
+  pkg: { workspaces?: NpmWorkspaces; catalog?: Record<string, string> },
+  version: string,
+): boolean {
+  const { workspaces } = pkg;
+  if (workspaces == null) {
+    return false;
+  }
+  // Mirrors `useWorkspacesCatalog` in rewriteBunCatalog.
+  const writesNestedCatalog =
+    !Array.isArray(workspaces) &&
+    (workspaces.catalog != null || (pkg.catalog == null && workspaces.catalogs != null));
+  return (
+    writesNestedCatalog ||
+    versionAtLeast(version, BUN_TOP_LEVEL_CATALOG_MIN_VERSION, ['latest', 'canary'])
+  );
+}
+
 // Whether a `catalog:` reference resolves for this package manager and version:
 // pnpm >= 9.5.0, Yarn >= 4.10.0, bun only inside a workspace, npm never. The
 // force-override `file:` guard is layered on by the bootstrap callers.
@@ -1021,7 +1048,13 @@ function rewriteCatalogObject(
     delete catalog[name];
   }
   if (VITEST_IS_MANAGED_OVERRIDE) {
-    for (const name of Object.keys(catalog)) {
+    // Like the pnpm catalog, add every declared alignable @vitest/* when the
+    // catalog owns `vitest`, so its new `catalog:` reference resolves. #2005
+    const names =
+      addMissing && 'vitest' in catalog
+        ? new Set([...Object.keys(catalog), ...vitestEcosystemPackages])
+        : Object.keys(catalog);
+    for (const name of names) {
       if (vitestEcosystemPackages.has(name) && isAlignableVitestEcosystemPackage(name)) {
         catalog[name] = VITEST_VERSION;
       }
@@ -1033,9 +1066,10 @@ function rewriteCatalogsObject(
   catalogs: Record<string, Record<string, string>>,
   usesVitest: boolean,
   vitestEcosystemPackages: ReadonlySet<string>,
+  targetCatalog?: Record<string, string>,
 ): void {
   for (const catalog of Object.values(catalogs)) {
-    rewriteCatalogObject(catalog, false, usesVitest, vitestEcosystemPackages);
+    rewriteCatalogObject(catalog, catalog === targetCatalog, usesVitest, vitestEcosystemPackages);
   }
 }
 
@@ -1069,14 +1103,23 @@ export function rewriteBunCatalog(
       pkg.workspaces && !Array.isArray(pkg.workspaces) ? pkg.workspaces : undefined;
     const useWorkspacesCatalog =
       workspacesObj?.catalog != null || (pkg.catalog == null && workspacesObj?.catalogs != null);
-    const catalog: Record<string, string> = {
-      ...(useWorkspacesCatalog ? workspacesObj?.catalog : pkg.catalog),
-    };
-
-    rewriteCatalogObject(catalog, true, usesVitest, vitestEcosystemPackages);
+    // Like the pnpm catalog, add missing entries to the catalog the new
+    // `catalog:` references point at. A named one such as `catalogs.build`
+    // takes them instead of a newly created default catalog.
+    const { preferredCatalogSpec } = readBunCatalogDependencyResolver(pkg);
+    const preferredName = preferredCatalogSpec.slice('catalog:'.length);
+    const namedTarget = preferredName
+      ? (workspacesObj?.catalogs?.[preferredName] ?? pkg.catalogs?.[preferredName])
+      : undefined;
+    const defaultCatalog = useWorkspacesCatalog ? workspacesObj?.catalog : pkg.catalog;
+    const catalog: Record<string, string> = { ...defaultCatalog };
+
+    rewriteCatalogObject(catalog, !namedTarget, usesVitest, vitestEcosystemPackages);
     pruneLegacyWrapperAliases(catalog);
 
-    if (useWorkspacesCatalog) {
+    if (namedTarget && !defaultCatalog) {
+      // No default catalog to update, and none is needed.
+    } else if (useWorkspacesCatalog) {
       workspacesObj.catalog = catalog;
       if (pkg.catalog) {
         rewriteCatalogObject(pkg.catalog, false, usesVitest, vitestEcosystemPackages);
@@ -1090,13 +1133,18 @@ export function rewriteBunCatalog(
       }
     }
     if (workspacesObj?.catalogs) {
-      rewriteCatalogsObject(workspacesObj.catalogs, usesVitest, vitestEcosystemPackages);
+      rewriteCatalogsObject(
+        workspacesObj.catalogs,
+        usesVitest,
+        vitestEcosystemPackages,
+        namedTarget,
+      );
       for (const named of Object.values(workspacesObj.catalogs)) {
         pruneLegacyWrapperAliases(named);
       }
     }
     if (pkg.catalogs) {
-      rewriteCatalogsObject(pkg.catalogs, usesVitest, vitestEcosystemPackages);
+      rewriteCatalogsObject(pkg.catalogs, usesVitest, vitestEcosystemPackages, namedTarget);
       for (const named of Object.values(pkg.catalogs)) {
         pruneLegacyWrapperAliases(named);
       }
@@ -1120,7 +1168,9 @@ export function rewriteBunCatalog(
         continue;
       }
       overrides[key] =
-        key === '@vitest/browser' ? value : getCatalogDependencySpec(current, value, true);
+        key === '@vitest/browser'
+          ? value
+          : getCatalogDependencySpec(current, value, true, { preferredCatalogSpec });
     }
     pkg.overrides = overrides;
 
@@ -1202,18 +1252,20 @@ export function rewriteRootWorkspacePackageJson(
       };
     } else if (packageManager === PackageManager.bun) {
       // bun overrides are handled in rewriteBunCatalog() with catalog: references
+      // when the workspace supports a catalog. Otherwise they stay concrete.
       // The browser override has no catalog entry and was pruned above with
       // stale bundled-package pins. Restore its current concrete version.
-      if (managed['@vitest/browser']) {
+      if (!supportCatalog) {
+        pkg.overrides = { ...pkg.overrides, ...managed };
+      } else if (managed['@vitest/browser']) {
         pkg.overrides = { ...pkg.overrides, '@vitest/browser': managed['@vitest/browser'] };
       }
       // Bun walks transitive peer-deps before resolving overrides; vitest 4.1.9
       // declares peer `vite ^6 || ^7 || ^8` and aborts unless `vite` is a direct
       // dep at the workspace root. Mirror the override as a devDep; the override
-      // configured in rewriteBunCatalog still redirects it to vite-plus-core. A
-      // bun workspace root always manages a catalog, so the direct edge resolves
-      // to a `catalog:` reference. See https://github.com/oven-sh/bun/issues/8406.
-      setDirectViteEdge(pkg, true, catalogDependencyResolver);
+      // configured in rewriteBunCatalog still redirects it to vite-plus-core.
+      // See https://github.com/oven-sh/bun/issues/8406.
+      setDirectViteEdge(pkg, supportCatalog, catalogDependencyResolver);
     } else if (packageManager === PackageManager.pnpm) {
       const overrideKeys = Object.keys(managedOverridePackages(workspaceUsesVitest));
       const usePnpmWorkspaceSettings = pnpmSupportsWorkspaceSettings(pnpmVersion ?? '');
diff --git a/packages/cli/src/migration/migrator/orchestrators.ts b/packages/cli/src/migration/migrator/orchestrators.ts
index dc4a2c5550..3439df9ffe 100644
--- a/packages/cli/src/migration/migrator/orchestrators.ts
+++ b/packages/cli/src/migration/migrator/orchestrators.ts
@@ -3,10 +3,11 @@ import path from 'node:path';
 
 import { PackageManager, type WorkspaceInfo, type WorkspacePackage } from '../../types/index.ts';
 import { VITE_PLUS_NAME, VITE_PLUS_VERSION, isForceOverrideMode } from '../../utils/constants.ts';
-import { editJsonFile } from '../../utils/json.ts';
+import { editJsonFile, readJsonFile } from '../../utils/json.ts';
 import {
   applyBuildAllowanceToPackageJsonPnpm,
   applyYarnWorkspaceHoistingFix,
+  bunSupportsCatalog,
   cleanupDeprecatedTsconfigOptions,
   collectInjectedProviderNames,
   collectOxlintDependencyNames,
@@ -395,12 +396,16 @@ export function rewriteMonorepo(
     workspaceInfo.rootDir,
     workspaceInfo.packages,
   );
-  // Catalog support: pnpm >= 9.5.0, Yarn >= 4.10.0, bun in a workspace (always
-  // true here — this is the monorepo path). An older PM falls back to concrete.
+  // Catalog support: pnpm >= 9.5.0, Yarn >= 4.10.0, bun per `bunSupportsCatalog`.
+  // An older PM falls back to concrete.
   const supportCatalog = supportsCatalog(
     workspaceInfo.packageManager,
     workspaceInfo.downloadPackageManager.version,
-    true,
+    workspaceInfo.packageManager === PackageManager.bun &&
+      bunSupportsCatalog(
+        readJsonFile(path.join(workspaceInfo.rootDir, 'package.json')),
+        workspaceInfo.downloadPackageManager.version,
+      ),
   );
   const workspaceContext = {
     rootDir: workspaceInfo.rootDir,
@@ -419,7 +424,7 @@ export function rewriteMonorepo(
       providerCatalogAdditions,
       supportCatalog,
     );
-  } else if (workspaceInfo.packageManager === PackageManager.bun) {
+  } else if (workspaceInfo.packageManager === PackageManager.bun && supportCatalog) {
     rewriteBunCatalog(
       workspaceInfo.rootDir,
       workspaceUsesVitest,
diff --git a/packages/cli/src/migration/migrator/vite-plus-bootstrap.ts b/packages/cli/src/migration/migrator/vite-plus-bootstrap.ts
index 5a4105b168..5a4197d669 100644
--- a/packages/cli/src/migration/migrator/vite-plus-bootstrap.ts
+++ b/packages/cli/src/migration/migrator/vite-plus-bootstrap.ts
@@ -32,6 +32,7 @@ import {
   pnpmPackageJsonSettingsPending,
   pnpmSupportsWorkspaceSettings,
   supportsCatalog,
+  bunSupportsCatalog,
   pnpmWorkspaceMinimumReleaseAgeExemptionsPending,
   projectUsesVitestDirectly,
   pruneLegacyWrapperAliases,
@@ -67,24 +68,6 @@ import {
   type PnpmPackageJsonSettings,
 } from './shared.ts';
 
-// Bun resolves `catalog:` references (and a top-level `catalog` field) ONLY
-// inside a workspace: a root package.json declaring a non-empty `workspaces`
-// (the array form, or the object `{ packages: [...] }` form). A standalone bun
-// project has nowhere to resolve a catalog from, so converting its edges to
-// `catalog:` makes `bun install` abort with "vite@catalog: failed to resolve".
-// The upgrade path must keep standalone bun on concrete specs, mirroring the
-// fresh path: `supportCatalog` is false for standalone bun (orchestrators.ts)
-// and `rewriteBunCatalog` runs only on monorepo roots (orchestrators.ts).
-function bunWorkspaceDeclaresPackages(workspaces: NpmWorkspaces | undefined): boolean {
-  if (Array.isArray(workspaces)) {
-    return workspaces.length > 0;
-  }
-  if (workspaces && typeof workspaces === 'object') {
-    return Array.isArray(workspaces.packages) && workspaces.packages.length > 0;
-  }
-  return false;
-}
-
 export type BootstrapPackageJson = {
   overrides?: Record<string, string>;
   resolutions?: Record<string, string>;
@@ -676,7 +659,8 @@ export function detectVitePlusBootstrapPending(
     supportsCatalog(
       packageManager,
       resolvedPackageManagerVersion,
-      packageManager === PackageManager.bun && bunWorkspaceDeclaresPackages(pkg.workspaces),
+      packageManager === PackageManager.bun &&
+        bunSupportsCatalog(pkg, resolvedPackageManagerVersion),
     );
   const catalogDependencyResolver = createCatalogDependencyResolver(projectPath, packageManager);
   const canonicalVitePlusSpec = supportCatalog
@@ -742,12 +726,18 @@ export function detectVitePlusBootstrapPending(
     // `catalog:` references, so the catalog resolver must NOT be consulted —
     // otherwise a dangling `catalog:` override resolves through the dead catalog
     // field and is mistaken for satisfied, masking the pending rewrite.
-    return !overridesSatisfyVitePlus(
-      pkg.overrides,
-      usesVitest,
-      supportCatalog ? readBunCatalogDependencyResolver(pkg) : undefined,
-      'bare',
-      usesWebdriverio,
+    const bunCatalogResolver = supportCatalog ? readBunCatalogDependencyResolver(pkg) : undefined;
+    // A `catalog:` vite-plus spec looks current, so judge its catalog value too.
+    return (
+      (supportCatalog &&
+        workspaceCatalogVitePlusDependencyPending(projectPath, packages, bunCatalogResolver)) ||
+      !overridesSatisfyVitePlus(
+        pkg.overrides,
+        usesVitest,
+        bunCatalogResolver,
+        'bare',
+        usesWebdriverio,
+      )
     );
   }
   if (packageManager === PackageManager.pnpm) {
@@ -979,15 +969,13 @@ export function ensureVitePlusBootstrap(
     workspaceInfo.packageManager === PackageManager.pnpm &&
     pnpmSupportsWorkspaceSettings(workspaceInfo.downloadPackageManager.version);
   // Catalogs only resolve inside a bun WORKSPACE (a root package.json with a
-  // non-empty `workspaces`). Gate both the catalog edges (`supportCatalog`) and
+  // `workspaces` field, even an empty one). Gate both the catalog edges (`supportCatalog`) and
   // the `rewriteBunCatalog` sink below on this so a standalone bun project keeps
   // concrete specs and writes no catalog field — otherwise `bun install` aborts
   // with "vite@catalog: failed to resolve".
   const isBunWorkspace =
     workspaceInfo.packageManager === PackageManager.bun &&
-    bunWorkspaceDeclaresPackages(
-      (readJsonFile(packageJsonPath) as { workspaces?: NpmWorkspaces }).workspaces,
-    );
+    bunSupportsCatalog(readJsonFile(packageJsonPath), workspaceInfo.downloadPackageManager.version);
   const supportCatalog =
     !VITE_PLUS_VERSION.startsWith('file:') &&
     supportsCatalog(