diff --git a/src/infra/tsdown-config.test.ts b/src/infra/tsdown-config.test.ts
index c955400bbf8..2d8be8485be 100644
--- a/src/infra/tsdown-config.test.ts
+++ b/src/infra/tsdown-config.test.ts
@@ -9,6 +9,9 @@ type TsdownConfigEntry = {
   entry?: Record<string, string> | string[];
   inputOptions?: TsdownInputOptions;
   outDir?: string;
+  outputOptions?: (options: unknown) => {
+    chunkFileNames?: (chunkInfo: { name: string; moduleIds: string[] }) => string;
+  };
 };
 
 type TsdownLog = {
@@ -145,4 +148,117 @@ describe("tsdown config", () => {
 
     expect(handled).toEqual([log]);
   });
+
+  it("routes bundled plugin shared chunks to their own directory", () => {
+    const configs = asConfigArray(tsdownConfig);
+    const unifiedGraph = configs.find((config) => entryKeys(config).includes("index"));
+    expect(unifiedGraph).toBeDefined();
+
+    // Extract the chunkFileNames function from outputOptions
+    const outputOptionsFn = unifiedGraph!.outputOptions;
+    expect(typeof outputOptionsFn).toBe("function");
+
+    const outputOptions = outputOptionsFn!({});
+    const chunkFileNames = outputOptions.chunkFileNames!;
+    expect(typeof chunkFileNames).toBe("function");
+
+    // Scenario 1: A chunk containing only slack files
+    expect(
+      chunkFileNames({
+        name: "shared-slack-api",
+        moduleIds: [
+          "extensions/slack/src/api.ts",
+          "extensions/slack/src/token.ts",
+        ],
+      }),
+    ).toBe("extensions/slack/[name]-[hash].js");
+
+    // Scenario 2: A chunk containing only telegram files
+    expect(
+      chunkFileNames({
+        name: "shared-telegram-api",
+        moduleIds: [
+          "extensions/telegram/src/api.ts",
+          "extensions/telegram/src/config.ts",
+        ],
+      }),
+    ).toBe("extensions/telegram/[name]-[hash].js");
+
+    // Scenario 3: A chunk containing mixed files (architectural violation)
+    expect(
+      chunkFileNames({
+        name: "shared-mixed",
+        moduleIds: [
+          "extensions/slack/src/api.ts",
+          "extensions/telegram/src/api.ts",
+        ],
+      }),
+    ).toBe("[name]-[hash].js");
+
+    // Scenario 4: A chunk containing only core files
+    expect(
+      chunkFileNames({
+        name: "shared-core",
+        moduleIds: [
+          "src/gateway/server-http.ts",
+          "src/gateway/client.ts",
+        ],
+      }),
+    ).toBe("[name]-[hash].js");
+
+    // Scenario 5: A chunk containing plugin and core files
+    expect(
+      chunkFileNames({
+        name: "shared-plugin-and-core",
+        moduleIds: [
+          "extensions/slack/src/api.ts",
+          "src/gateway/server-http.ts",
+        ],
+      }),
+    ).toBe("[name]-[hash].js");
+
+    // Scenario 5b: A chunk containing plugin files and virtual modules
+    expect(
+      chunkFileNames({
+        name: "shared-plugin-with-virtual",
+        moduleIds: [
+          "extensions/slack/src/api.ts",
+          "\0commonjsHelpers.js",
+        ],
+      }),
+    ).toBe("extensions/slack/[name]-[hash].js");
+
+    // Scenario 5c: A chunk containing plugin files and node_modules dependencies
+    expect(
+      chunkFileNames({
+        name: "shared-plugin-with-deps",
+        moduleIds: [
+          "extensions/slack/src/api.ts",
+          "node_modules/@slack/web-api/index.js",
+        ],
+      }),
+    ).toBe("extensions/slack/[name]-[hash].js");
+
+    // Scenario 6: Fallback to previous function
+    const outputOptionsWithFn = outputOptionsFn!({
+      chunkFileNames: () => "custom-fn-[hash].js",
+    });
+    expect(
+      outputOptionsWithFn.chunkFileNames!({
+        name: "shared-core",
+        moduleIds: ["src/gateway/server-http.ts"],
+      }),
+    ).toBe("custom-fn-[hash].js");
+
+    // Scenario 7: Fallback to previous string
+    const outputOptionsWithStr = outputOptionsFn!({
+      chunkFileNames: "custom-str-[hash].js",
+    });
+    expect(
+      outputOptionsWithStr.chunkFileNames!({
+        name: "shared-core",
+        moduleIds: ["src/gateway/server-http.ts"],
+      }),
+    ).toBe("custom-str-[hash].js");
+  });
 });
diff --git a/tsdown.config.ts b/tsdown.config.ts
index 0d7973cca81..70842b681fe 100644
--- a/tsdown.config.ts
+++ b/tsdown.config.ts
@@ -88,6 +88,44 @@ function nodeBuildConfig(config: UserConfig): UserConfig {
     fixedExtension: false,
     platform: "node",
     inputOptions: buildInputOptions,
+    outputOptions(options) {
+      const previousChunkFileNames = options.chunkFileNames;
+      return {
+        ...options,
+        chunkFileNames(chunkInfo) {
+          const moduleIds = chunkInfo.moduleIds || [];
+          const extensionIds = new Set<string>();
+          let hasNonPluginModules = false;
+          for (const id of moduleIds) {
+            if (id.startsWith("\0")) {
+              continue;
+            }
+            const absoluteId = path.resolve(process.cwd(), id);
+            const relativeToRoot = path.relative(process.cwd(), absoluteId);
+            const parts = relativeToRoot.split(path.sep);
+
+            if (parts[0] === "extensions" && parts.length > 2) {
+              extensionIds.add(parts[1]);
+            } else if (parts.includes("node_modules")) {
+              continue;
+            } else {
+              hasNonPluginModules = true;
+            }
+          }
+          if (extensionIds.size === 1 && !hasNonPluginModules) {
+            const extId = Array.from(extensionIds)[0];
+            return `extensions/${extId}/[name]-[hash].js`;
+          }
+          if (typeof previousChunkFileNames === "function") {
+            return previousChunkFileNames(chunkInfo);
+          }
+          if (typeof previousChunkFileNames === "string") {
+            return previousChunkFileNames;
+          }
+          return `[name]-[hash].js`;
+        },
+      };
+    },
   };
 }