diff --git a/packages/vinext/src/index.ts b/packages/vinext/src/index.ts
index db15cdb3..98ac869e 100644
--- a/packages/vinext/src/index.ts
+++ b/packages/vinext/src/index.ts
@@ -1507,14 +1507,14 @@ export default function vinext(options: VinextOptions = {}): PluginOption[] {
         appDir = path.join(baseDir, "app");
         hasPagesDir = fs.existsSync(pagesDir);
         hasAppDir = !options.disableAppRouter && fs.existsSync(appDir);
-        middlewarePath = findMiddlewareFile(root);
-        instrumentationPath = findInstrumentationFile(root);
 
         // Load next.config.js if present (always from project root, not src/)
         const phase = env?.command === "build" ? PHASE_PRODUCTION_BUILD : PHASE_DEVELOPMENT_SERVER;
         const rawConfig = await loadNextConfig(root, phase);
         nextConfig = await resolveNextConfig(rawConfig, root);
         fileMatcher = createValidFileMatcher(nextConfig.pageExtensions);
+        instrumentationPath = findInstrumentationFile(root, fileMatcher);
+        middlewarePath = findMiddlewareFile(root, fileMatcher);
 
         // Merge env from next.config.js with NEXT_PUBLIC_* env vars
         const defines = getNextPublicEnvDefines();
diff --git a/packages/vinext/src/server/instrumentation.ts b/packages/vinext/src/server/instrumentation.ts
index 0e084f03..20bd353e 100644
--- a/packages/vinext/src/server/instrumentation.ts
+++ b/packages/vinext/src/server/instrumentation.ts
@@ -39,6 +39,7 @@
 import fs from "node:fs";
 import path from "node:path";
 import { getRequestExecutionContext } from "../shims/request-context.js";
+import { ValidFileMatcher } from "../routing/file-matcher.js";
 /**
  * Minimal duck-typed interface for the module runner passed to
  * `runInstrumentation`. Only `.import()` is used — this avoids requiring
@@ -63,26 +64,21 @@ export async function importModule(
   return (await runner.import(id)) as Record<string, any>;
 }
 
-/** Possible instrumentation file names. */
-const INSTRUMENTATION_FILES = [
-  "instrumentation.ts",
-  "instrumentation.tsx",
-  "instrumentation.js",
-  "instrumentation.mjs",
-  "src/instrumentation.ts",
-  "src/instrumentation.tsx",
-  "src/instrumentation.js",
-  "src/instrumentation.mjs",
-];
+const INSTRUMENTATION_LOCATIONS = ["", "src/"];
 
 /**
  * Find the instrumentation file in the project root.
  */
-export function findInstrumentationFile(root: string): string | null {
-  for (const file of INSTRUMENTATION_FILES) {
-    const fullPath = path.join(root, file);
-    if (fs.existsSync(fullPath)) {
-      return fullPath;
+export function findInstrumentationFile(
+  root: string,
+  fileMatcher: ValidFileMatcher,
+): string | null {
+  for (const dir of INSTRUMENTATION_LOCATIONS) {
+    for (const ext of fileMatcher.dottedExtensions) {
+      const fullPath = path.join(root, dir, `instrumentation${ext}`);
+      if (fs.existsSync(fullPath)) {
+        return fullPath;
+      }
     }
   }
   return null;
diff --git a/packages/vinext/src/server/middleware.ts b/packages/vinext/src/server/middleware.ts
index efdce4ad..0244f3dd 100644
--- a/packages/vinext/src/server/middleware.ts
+++ b/packages/vinext/src/server/middleware.ts
@@ -32,6 +32,7 @@ import { NextRequest, NextFetchEvent } from "../shims/server.js";
 import { normalizePath } from "./normalize-path.js";
 import { shouldKeepMiddlewareHeader } from "./middleware-request-headers.js";
 import { normalizePathnameForRouteMatchStrict } from "../routing/utils.js";
+import { ValidFileMatcher } from "../routing/file-matcher.js";
 
 /**
  * Determine whether a middleware/proxy file path refers to a proxy file.
@@ -73,53 +74,35 @@ export function resolveMiddlewareHandler(mod: Record<string, unknown>, filePath:
   return handler as Function;
 }
 
-/**
- * Possible proxy/middleware file names.
- * proxy.ts (Next.js 16) is checked first, then middleware.ts (deprecated).
- */
-const PROXY_FILES = [
-  "proxy.ts",
-  "proxy.js",
-  "proxy.mjs",
-  "src/proxy.ts",
-  "src/proxy.js",
-  "src/proxy.mjs",
-];
-
-const MIDDLEWARE_FILES = [
-  "middleware.ts",
-  "middleware.tsx",
-  "middleware.js",
-  "middleware.mjs",
-  "src/middleware.ts",
-  "src/middleware.tsx",
-  "src/middleware.js",
-  "src/middleware.mjs",
-];
+const MIDDLEWARE_LOCATIONS = ["", "src/"];
 
 /**
  * Find the proxy or middleware file in the project root.
  * Checks for proxy.ts (Next.js 16) first, then falls back to middleware.ts.
  * If middleware.ts is found, logs a deprecation warning.
  */
-export function findMiddlewareFile(root: string): string | null {
+export function findMiddlewareFile(root: string, fileMatcher: ValidFileMatcher): string | null {
   // Check proxy.ts first (Next.js 16 replacement for middleware.ts)
-  for (const file of PROXY_FILES) {
-    const fullPath = path.join(root, file);
-    if (fs.existsSync(fullPath)) {
-      return fullPath;
+  for (const dir of MIDDLEWARE_LOCATIONS) {
+    for (const ext of fileMatcher.dottedExtensions) {
+      const fullPath = path.join(root, dir, `proxy${ext}`);
+      if (fs.existsSync(fullPath)) {
+        return fullPath;
+      }
     }
   }
 
   // Fall back to middleware.ts (deprecated in Next.js 16)
-  for (const file of MIDDLEWARE_FILES) {
-    const fullPath = path.join(root, file);
-    if (fs.existsSync(fullPath)) {
-      console.warn(
-        "[vinext] middleware.ts is deprecated in Next.js 16. " +
-          "Rename to proxy.ts and export a default or named proxy function.",
-      );
-      return fullPath;
+  for (const dir of MIDDLEWARE_LOCATIONS) {
+    for (const ext of fileMatcher.dottedExtensions) {
+      const fullPath = path.join(root, dir, `middleware${ext}`);
+      if (fs.existsSync(fullPath)) {
+        console.warn(
+          "[vinext] middleware.ts is deprecated in Next.js 16. " +
+            "Rename to proxy.ts and export a default or named proxy function.",
+        );
+        return fullPath;
+      }
     }
   }
   return null;
diff --git a/tests/features.test.ts b/tests/features.test.ts
index e00e14c2..d1f1096d 100644
--- a/tests/features.test.ts
+++ b/tests/features.test.ts
@@ -20,6 +20,7 @@ import {
   requestNodeServerWithHost,
   startFixtureServer,
 } from "./helpers.js";
+import { createValidFileMatcher } from "../packages/vinext/src/routing/file-matcher.js";
 
 const FIXTURE_DIR = PAGES_FIXTURE_DIR;
 
@@ -2817,7 +2818,7 @@ describe("instrumentation.ts support", () => {
   it("findInstrumentationFile returns null when no file exists", async () => {
     const { findInstrumentationFile } =
       await import("../packages/vinext/src/server/instrumentation.js");
-    const result = findInstrumentationFile("/nonexistent/path");
+    const result = findInstrumentationFile("/nonexistent/path", createValidFileMatcher());
     expect(result).toBeNull();
   });
 
@@ -2835,7 +2836,7 @@ describe("instrumentation.ts support", () => {
       'export function register() { console.log("registered"); }',
     );
 
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
     expect(result).toBe(path.join(tmpDir, "instrumentation.ts"));
 
     // Cleanup
@@ -2856,7 +2857,7 @@ describe("instrumentation.ts support", () => {
       "export function register() {}",
     );
 
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
     expect(result).toBe(path.join(tmpDir, "src", "instrumentation.ts"));
 
     fs.rmSync(tmpDir, { recursive: true });
diff --git a/tests/instrumentation.test.ts b/tests/instrumentation.test.ts
index 18598f00..e2481d9a 100644
--- a/tests/instrumentation.test.ts
+++ b/tests/instrumentation.test.ts
@@ -3,6 +3,7 @@ import fs from "node:fs";
 import os from "node:os";
 import path from "node:path";
 import { findInstrumentationFile } from "../packages/vinext/src/server/instrumentation.js";
+import { createValidFileMatcher } from "../packages/vinext/src/routing/file-matcher.js";
 
 // The runInstrumentation/reportRequestError describe blocks re-import via
 // vi.resetModules() to get fresh module-level state (_onRequestError).
@@ -22,7 +23,7 @@ describe("findInstrumentationFile", () => {
   it("returns the path when a file exists at root", () => {
     fs.writeFileSync(path.join(tmpDir, "instrumentation.ts"), "");
 
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
 
     expect(result).toBe(path.join(tmpDir, "instrumentation.ts"));
   });
@@ -33,7 +34,7 @@ describe("findInstrumentationFile", () => {
     fs.mkdirSync(path.join(tmpDir, "src"));
     fs.writeFileSync(path.join(tmpDir, "src", "instrumentation.ts"), "");
 
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
 
     // Root files come first in INSTRUMENTATION_FILES, so root wins
     expect(result).toBe(path.join(tmpDir, "instrumentation.ts"));
@@ -43,13 +44,13 @@ describe("findInstrumentationFile", () => {
     fs.mkdirSync(path.join(tmpDir, "src"));
     fs.writeFileSync(path.join(tmpDir, "src", "instrumentation.ts"), "");
 
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
 
     expect(result).toBe(path.join(tmpDir, "src", "instrumentation.ts"));
   });
 
   it("returns null when no instrumentation file exists", () => {
-    const result = findInstrumentationFile(tmpDir);
+    const result = findInstrumentationFile(tmpDir, createValidFileMatcher());
 
     expect(result).toBeNull();
   });
diff --git a/tests/shims.test.ts b/tests/shims.test.ts
index 5000242d..3b714fc2 100644
--- a/tests/shims.test.ts
+++ b/tests/shims.test.ts
@@ -2107,30 +2107,64 @@ describe("replyToCacheKey deterministic hashing", () => {
 describe("middleware runner", () => {
   it("findMiddlewareFile finds middleware.ts at project root", async () => {
     const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
     // pages-basic fixture has middleware.ts
-    const result = findMiddlewareFile(FIXTURE_DIR);
+    const result = findMiddlewareFile(FIXTURE_DIR, createValidFileMatcher());
     expect(result).not.toBeNull();
     expect(result).toContain("middleware.ts");
   });
 
   it("findMiddlewareFile returns null when no middleware exists", async () => {
     const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
-    const result = findMiddlewareFile("/tmp/nonexistent-dir-" + Date.now());
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
+    const result = findMiddlewareFile(
+      "/tmp/nonexistent-dir-" + Date.now(),
+      createValidFileMatcher(),
+    );
+    expect(result).toBeNull();
+  });
+
+  it("findMiddlewareFile does not find middleware.ts when ts is not a configured pageExtension", async () => {
+    const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
+    // FIXTURE_DIR has middleware.ts — restricting to mdx only means it should not match
+    const result = findMiddlewareFile(FIXTURE_DIR, createValidFileMatcher(["mdx"]));
     expect(result).toBeNull();
   });
 
+  it("findMiddlewareFile emits a deprecation warning when middleware.ts is found", async () => {
+    const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
+    const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});
+    try {
+      findMiddlewareFile(FIXTURE_DIR, createValidFileMatcher());
+      expect(warnSpy).toHaveBeenCalledOnce();
+      expect(warnSpy).toHaveBeenCalledWith(
+        expect.stringContaining("middleware.ts is deprecated in Next.js 16"),
+      );
+    } finally {
+      warnSpy.mockRestore();
+    }
+  });
+
   it("findMiddlewareFile prefers proxy.ts over middleware.ts (Next.js 16)", async () => {
     const fs = await import("node:fs");
     const path = await import("node:path");
     const os = await import("node:os");
     const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
 
     // Create a temp directory with both proxy.ts and middleware.ts
     const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "vinext-proxy-test-"));
     try {
       fs.writeFileSync(path.join(tmpDir, "proxy.ts"), "export default function proxy() {}");
       fs.writeFileSync(path.join(tmpDir, "middleware.ts"), "export function middleware() {}");
-      const result = findMiddlewareFile(tmpDir);
+      const result = findMiddlewareFile(tmpDir, createValidFileMatcher());
       expect(result).not.toBeNull();
       expect(result).toContain("proxy.ts");
     } finally {
@@ -2143,11 +2177,13 @@ describe("middleware runner", () => {
     const path = await import("node:path");
     const os = await import("node:os");
     const { findMiddlewareFile } = await import("../packages/vinext/src/server/middleware.js");
+    const { createValidFileMatcher } =
+      await import("../packages/vinext/src/routing/file-matcher.js");
 
     const tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "vinext-proxy-test-"));
     try {
       fs.writeFileSync(path.join(tmpDir, "proxy.js"), "module.exports = function proxy() {}");
-      const result = findMiddlewareFile(tmpDir);
+      const result = findMiddlewareFile(tmpDir, createValidFileMatcher());
       expect(result).not.toBeNull();
       expect(result).toContain("proxy.js");
     } finally {