feat: update bun runtime to v1.4.0

.bun-version

@@ -1 +1 @@
-1.3.14
+1.4.0

README.md

@@ -5,7 +5,7 @@ A custom [Bun](https://bun.sh) runtime for AWS Lambda with CDK constructs for ea
 > [!NOTE]
 > **v3 is ESM-only and no longer published as a jsii package.** Polyglot CDK support (Python, Java, .NET) has been removed — there were zero consumers. If you need the layer without CDK, the zip is available as a GitHub Release asset. See [ADR: Drop jsii](docs/adr-drop-jsii.md) for the full rationale.
 
-Current bun version: [1.3.14](https://bun.sh/blog/bun-v1.3.14)
+Current bun version: [1.4.0](https://bun.sh/blog/bun-v1.4.0)
 
 ## Installation
 

src/index.ts

@@ -7,7 +7,7 @@ import type { LayerVersionProps } from "aws-cdk-lib/aws-lambda";
 import { LogGroup, RetentionDays } from "aws-cdk-lib/aws-logs";
 import type { Construct } from "constructs";
 
-const bunVersion = "1.3.14";
+const bunVersion = "1.4.0";
 
 export interface BunFunctionProps extends Omit<
   FunctionProps,

test/buildLayer.test.ts

@@ -1,4 +1,9 @@
 import { describe, expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { resolve } from "node:path";
+
+const srcIndex = readFileSync(resolve(__dirname, "../src/index.ts"), "utf8");
+const bunVersion = srcIndex.match(/const bunVersion = "([^"]+)"/)?.[1] ?? "";
 
 describe("version parameter precedence (Property 6)", () => {
   // Uses non-existent versions that pass validation but 404 at download (fast failure)
@@ -20,17 +25,12 @@ describe("version parameter precedence (Property 6)", () => {
   });
 
   test("falls back to src/index.ts version when both are absent", () => {
-    // The script resolves 1.3.14 from src/index.ts and starts downloading.
-    // We don't wait for the full download — just verify it found the right version.
-    // Use a fake non-downloadable version by temporarily patching would be complex,
-    // so instead we rely on the output showing the resolved version.
     const proc = Bun.spawnSync(["bun", "command/buildLayer.ts"], {
       env: { ...process.env, BUN_VERSION: undefined },
       timeout: 3000,
     });
     const output = proc.stdout.toString() + proc.stderr.toString();
-    // The script should print "Downloading Bun v1.3.14" proving it read src/index.ts
-    expect(output).toContain("1.3.14");
+    expect(output).toContain(bunVersion);
   });
 });
 

test/constructs.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test, beforeAll, afterAll } from "bun:test";
-import { existsSync, writeFileSync, unlinkSync } from "node:fs";
+import { existsSync, readFileSync, writeFileSync, unlinkSync } from "node:fs";
 import { resolve } from "node:path";
 
 import { App, Stack } from "aws-cdk-lib";
@@ -8,8 +8,11 @@ import * as fc from "fast-check";
 
 import { BunFunction, BunLambdaLayer } from "../src/index";
 
+const srcIndex = readFileSync(resolve(__dirname, "../src/index.ts"), "utf8");
+const bunVersion = srcIndex.match(/const bunVersion = "([^"]+)"/)?.[1] ?? "";
+
 // CDK's Code.fromAsset requires the zip to exist on disk during synth
-const dummyZipPath = resolve(__dirname, "../src/bun-lambda-layer-1.3.14.zip");
+const dummyZipPath = resolve(__dirname, `../src/bun-lambda-layer-${bunVersion}.zip`);
 
 beforeAll(() => {
   if (!existsSync(dummyZipPath)) {