diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3da84ddc0..8c6a0884f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -40,6 +40,8 @@ All notable changes to this project will be documented in this file.
 
 ### Changed
 
+- **nix/bun**: Overlay nixpkgs' Bun package to `1.3.14-canary.1+ca9e0896c` with fixed-output hashes so repo builds use the module-loader rewrite that fixes concurrent dynamic import TDZ failures before a stable `bun-v1.3.14` release asset is available.
+- **@overeng/tui-stories**: Restore concurrent story module imports on Bun `1.3.14+` and non-Bun runtimes now that Bun fixed the dynamic `import()` TDZ bug in oven-sh/bun#29393; older Bun versions keep the sequential compatibility path.
 - **@overeng/notion-react**: `<Page>` and `<ChildPage>` accept `icon={null}` and `cover={null}` as explicit clear sentinels (#618). Dropping the prop is still "no claim" (preserves server state); passing `null` emits `pages.update({icon: null})` / `pages.update({cover: null})`. On a fresh page with no prior icon/cover, `null` is a no-op.
 - **@overeng/notion-react**: Same-parent `<ChildPage>` creates are now sequential — JSX order is preserved 1:1 on the server (#618). Parallel `pages.create` under a common parent yields nondeterministic `child_page` ordering; the driver issues sequential POSTs so no post-create re-fetch is needed. T08 (formerly "concurrent sibling-page order is not authoritative") is now a normative invariant; the deferred `ensureSiblingOrder` sync option is dropped.
 - **@overeng/notion-react**: `CACHE_SCHEMA_VERSION` bumped `2 → 3` to accommodate per-page cache subtrees (#618). v2 caches fall through the existing `"schema-mismatch"` cold path — transparent, no caller action required. The first sync after upgrade may emit one spurious metadata update per sub-page as response-normalized title/icon/cover is recomputed.
diff --git a/context/workarounds/bun-issues.md b/context/workarounds/bun-issues.md
index 95cfbc002..fab7dd641 100644
--- a/context/workarounds/bun-issues.md
+++ b/context/workarounds/bun-issues.md
@@ -56,6 +56,17 @@ This aligns with our pnpm pattern - see "Bun Workspace Pattern" section below.
 
 ## Additional Blocking Issues
 
+### Resolved Runtime Issues
+
+#### BUN-04: Concurrent dynamic import TDZ
+
+- [Concurrent dynamic import with top-level await triggers temporal dead zone](https://github.com/oven-sh/bun/issues/20489)
+- Fixed by [oven-sh/bun#29393](https://github.com/oven-sh/bun/pull/29393), shipped in Bun `1.3.14`.
+
+`effect-utils` overlays nixpkgs' Bun package to `1.3.14-canary.1+ca9e0896c` while no stable `bun-v1.3.14` release asset exists. The overlay uses fixed-output hashes for the GitHub canary release assets.
+
+`@overeng/tui-stories` keeps a runtime compatibility gate for downstreams that provide their own Bun: Bun `<1.3.14` imports story modules sequentially; Bun `>=1.3.14` and non-Bun runtimes import concurrently.
+
 ### BUN-03: Bun patchedDependencies bug
 
 - [Patching falls over when using local path dependencies](https://github.com/oven-sh/bun/issues/13531)
diff --git a/devenv.nix b/devenv.nix
index 600f690ca..8b5591afd 100644
--- a/devenv.nix
+++ b/devenv.nix
@@ -7,7 +7,13 @@
 }:
 let
   repoFlake = builtins.getFlake (toString ./.);
-  flakePkgs = import repoFlake.inputs.nixpkgs { inherit (pkgs) system; };
+  # TODO: Drop this overlay once nixpkgs ships a stable Bun version with
+  # oven-sh/bun#29393 (>= 1.3.14).
+  bunOverlay = import ./nix/bun-overlay.nix;
+  flakePkgs = import repoFlake.inputs.nixpkgs {
+    inherit (pkgs) system;
+    overlays = [ bunOverlay ];
+  };
   cliBuildStamp = import ./nix/workspace-tools/lib/cli-build-stamp.nix { inherit pkgs; };
   # Use npm oxlint with NAPI bindings to enable JavaScript plugin support
   oxlintNpm = import ./nix/oxlint-npm.nix {
@@ -42,7 +48,7 @@ let
     context = ./nix/devenv-modules/tasks/shared/context.nix;
   };
   # Use bun source entrypoints for in-repo CLIs in devenv (flake builds stay strict).
-  mkSourceCli = import ./nix/devenv-modules/lib/mk-source-cli.nix { inherit pkgs; };
+  mkSourceCli = import ./nix/devenv-modules/lib/mk-source-cli.nix { pkgs = flakePkgs; };
 
   # CLI packages built with Nix (for hash management)
   nixCliPackages = [
@@ -371,7 +377,7 @@ in
     inputs.tsgo.packages.${pkgs.system}.effect-tsgo
     (import ./nix/pnpm.nix { inherit pkgs; })
     pkgs.nodejs_24
-    pkgs.bun
+    flakePkgs.bun
     pkgs.typescript
     pkgs.flock # Cross-process locking for setup tasks (see setup.nix)
     oxlintWithPlugins
diff --git a/flake.nix b/flake.nix
index f06399b54..24d31c04e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -29,11 +29,17 @@
       # lastModified is the git commit timestamp (Unix seconds)
       commitTs = self.sourceInfo.lastModified or 0;
       dirty = self.sourceInfo ? dirtyShortRev;
+      # TODO: Drop this overlay once nixpkgs ships a stable Bun version with
+      # oven-sh/bun#29393 (>= 1.3.14).
+      bunOverlay = import ./nix/bun-overlay.nix;
     in
     flake-utils.lib.eachDefaultSystem (
       system:
       let
-        pkgs = import nixpkgs { inherit system; };
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ bunOverlay ];
+        };
         mkBunCli = import ./nix/workspace-tools/lib/mk-bun-cli.nix { inherit pkgs; };
         cliBuildStamp = import ./nix/workspace-tools/lib/cli-build-stamp.nix { inherit pkgs; };
         rootPath = self.outPath;
@@ -105,6 +111,7 @@
       in
       {
         packages = cliPackages // {
+          bun = pkgs.bun;
           cli-build-stamp = cliBuildStamp.package;
           effect-tsgo = tsgo.packages.${system}.effect-tsgo;
           genie-dirty = cliPackagesDirty.genie;
@@ -147,6 +154,8 @@
       }
     )
     // {
+      overlays.default = bunOverlay;
+
       # Devenv modules for importing into other repos
       devenvModules = {
         # `dt` command wrapper for devenv tasks with shell completions
diff --git a/nix/bun-overlay.nix b/nix/bun-overlay.nix
new file mode 100644
index 000000000..90571bb27
--- /dev/null
+++ b/nix/bun-overlay.nix
@@ -0,0 +1,41 @@
+final: prev:
+let
+  version = "1.3.14-canary.1+ca9e0896c";
+
+  canarySource =
+    system: hash:
+    final.fetchurl {
+      # Bun has not published a stable bun-v1.3.14 release asset yet. The
+      # canary release channel is mutable upstream, but the fixed-output hash
+      # pins the exact post-module-loader-rewrite binary we want here.
+      url = "https://github.com/oven-sh/bun/releases/download/canary/bun-${system}.zip";
+      inherit hash;
+    };
+in
+{
+  bun = prev.bun.overrideAttrs (
+    finalAttrs: prevAttrs: {
+      inherit version;
+
+      src =
+        finalAttrs.passthru.sources.${prev.stdenvNoCC.hostPlatform.system}
+          or (throw "Unsupported system: ${prev.stdenvNoCC.hostPlatform.system}");
+
+      passthru = prevAttrs.passthru // {
+        sources = {
+          "aarch64-darwin" =
+            canarySource "darwin-aarch64" "sha256-CvRCXIsSTDxEznoCwT04SDGD+GapVBazNOVyVSKuPYA=";
+          "aarch64-linux" =
+            canarySource "linux-aarch64" "sha256-0ys2Rh1g5rHvXy4X/XNWufIorsn5sVqT1sJathUtBFo=";
+          "x86_64-darwin" =
+            canarySource "darwin-x64-baseline" "sha256-yScvX5uhuUPWVz6yAwchiqdaFty/em4rc17p4xLxg1s=";
+          "x86_64-linux" = canarySource "linux-x64" "sha256-Adt21Dh4wMhI7rCEdgp83xKzY4gUAOjeFkc73EaaJlA=";
+        };
+      };
+
+      meta = prevAttrs.meta // {
+        changelog = "https://github.com/oven-sh/bun/compare/af24e281e...ca9e0896c";
+      };
+    }
+  );
+}
diff --git a/packages/@overeng/tui-stories/src/StoryDiscovery.ts b/packages/@overeng/tui-stories/src/StoryDiscovery.ts
index ecba7d419..d47c05953 100644
--- a/packages/@overeng/tui-stories/src/StoryDiscovery.ts
+++ b/packages/@overeng/tui-stories/src/StoryDiscovery.ts
@@ -70,6 +70,28 @@ export interface DiscoverStoriesResult {
   readonly skippedCount: number
 }
 
+type StoryImportConcurrency = 1 | 'unbounded'
+
+const bunVersionSupportsConcurrentDynamicImport = (version: string): boolean => {
+  const [major = 0, minor = 0, patch = 0] = version
+    .split('.')
+    .map((part) => Number.parseInt(part, 10))
+    .map((part) => (Number.isNaN(part) === true ? 0 : part))
+
+  return major > 1 || (major === 1 && (minor > 3 || (minor === 3 && patch >= 14)))
+}
+
+/** Return safe story import concurrency for the active JavaScript runtime. */
+export const storyImportConcurrencyForRuntime = (
+  bunVersion: string | undefined = process.versions.bun,
+): StoryImportConcurrency => {
+  if (bunVersion === undefined) return 'unbounded'
+
+  // Fixed by Bun's module-loader rewrite in 1.3.14:
+  // https://github.com/oven-sh/bun/issues/20489
+  return bunVersionSupportsConcurrentDynamicImport(bunVersion) === true ? 'unbounded' : 1
+}
+
 /** Discover and parse all story files in the given package directories */
 export const discoverStories = (options: {
   readonly packageDirs: readonly string[]
@@ -84,15 +106,9 @@ export const discoverStories = (options: {
       return { modules: [], skippedCount: 0 }
     }
 
-    /* Sequential imports to avoid Bun's ESM TDZ bug: when concurrent import() calls
-       share a dependency and one chain fails (e.g. missing module), Bun leaves the shared
-       module's bindings uninitialized for other importers. With the shared
-       @overeng/tui-react/storybook dependency this caused ~100% TDZ failure rate.
-       Performance is unaffected — shared modules are cached after first evaluation.
-       See: https://github.com/oven-sh/bun/issues/20489 */
     const results = yield* Effect.all(
       filePaths.map((fp) => importStoryFile(fp)),
-      { concurrency: 1 },
+      { concurrency: storyImportConcurrencyForRuntime() },
     )
 
     const modules = results.filter((m): m is ParsedStoryModule => m !== undefined)
diff --git a/packages/@overeng/tui-stories/test/StoryDiscovery.test.ts b/packages/@overeng/tui-stories/test/StoryDiscovery.test.ts
index 142af770d..0fe7299b1 100644
--- a/packages/@overeng/tui-stories/test/StoryDiscovery.test.ts
+++ b/packages/@overeng/tui-stories/test/StoryDiscovery.test.ts
@@ -3,7 +3,7 @@ import { resolve } from 'node:path'
 import { describe, it, expect } from '@effect/vitest'
 import { Effect } from 'effect'
 
-import { discoverStories } from '../src/StoryDiscovery.ts'
+import { discoverStories, storyImportConcurrencyForRuntime } from '../src/StoryDiscovery.ts'
 import { parseStoryModule } from '../src/StoryModule.ts'
 
 const WORKSPACE_ROOT = resolve(import.meta.dirname, '../../../..')
@@ -39,6 +39,13 @@ describe('StoryDiscovery', () => {
     }),
   )
 
+  it('uses concurrent story imports outside affected Bun versions', () => {
+    expect(storyImportConcurrencyForRuntime(undefined)).toBe('unbounded')
+    expect(storyImportConcurrencyForRuntime('1.3.13')).toBe(1)
+    expect(storyImportConcurrencyForRuntime('1.3.14')).toBe('unbounded')
+    expect(storyImportConcurrencyForRuntime('1.4.0')).toBe('unbounded')
+  })
+
   it('parseStoryModule handles valid exports', () => {
     const mod = parseStoryModule({
       exports: {