diff --git a/AGENTS.md b/AGENTS.md
index 098dc16e2..09d82b203 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -93,7 +93,7 @@ Adding a cross-boundary feature:
 - **Source policy (Vitest registry):** file-local / small-glob invariants live in [`src/architecture/sourcePolicyRules.ts`](src/architecture/sourcePolicyRules.ts) + walker [`sourcePolicy.ts`](src/architecture/sourcePolicy.ts) — prefer adding a rule there over a new `scripts/check-*.mjs`. Suppress with `// source-policy-ok <rule-id> <reason>`. Pre-commit always appends `src/architecture/sourcePolicy.test.ts` when any TypeScript under `src/` is staged (the registry is not import-related). Keep cross-cutting always-on hygiene in existing `check:*` scanners.
 - **Reticulum sidecar (Rust):** Clippy + rustfmt via `pnpm run check:reticulum-sidecar` (full-feature fmt + Clippy + test when `cargo` is on `PATH` **and** sidecar-related paths are staged) and the same feature set in `reticulum-sidecar.yaml`. Coverage threshold (`cargo llvm-cov --fail-under-lines`) is enforced only in `tests.yaml` when sidecar paths change — not in pre-commit.
 - **Temp dirs in tests:** Use `mkdtempSync(path.join(os.tmpdir(), 'prefix-'))` — never write to a fixed name under `os.tmpdir()` (CodeQL + `check:insecure-temp-files`).
-- Vitest worker pool sizes and shared Vite dep inline lists live in `vitest.harness.ts` — update when adding deps that need inlining.
+- Vitest worker pool sizes and shared Vite dep inline lists live in `vitest.harness.mts` — update when adding deps that need inlining.
 - Prefer `mockConsoleWarn` / `withMockedConsoleWarn` from `src/renderer/lib/vitestConsoleMock.ts` over ad-hoc `vi.spyOn(console, 'warn')` in renderer tests.
 - Monolithic runtimes (`useMeshtasticRuntime`, `useMeshcoreRuntime`, `noble-ble-manager`) may use **source contract tests** (`sourceContractTestHelpers.ts`, `*.reconnect*.test.ts`) when full integration mocking is impractical — see [development-environment.md](docs/development-environment.md#vitest-projects-and-worker-allocation). Runtime contract tests that load `use*Runtime.ts` must use `loadRuntimeSource()` (enforced by source policy).
 - Mock console before spying logged errors: `vi.spyOn(console, 'warn').mockImplementation(() => {})` in `beforeEach` when shared.
diff --git a/ARCHITECTURE.md b/ARCHITECTURE.md
index dbd46d3e7..2ba1d16af 100644
--- a/ARCHITECTURE.md
+++ b/ARCHITECTURE.md
@@ -16,7 +16,7 @@ Path alias `@/*` maps to `src/*` (see `tsconfig.json`).
 
 **Entry points:** `src/main/index.ts`, `src/preload/index.ts`, `src/renderer/main.tsx`, `src/renderer/App.tsx`.
 
-**Repo root (not exhaustive):** `.github/workflows/`, `scripts/check-*.mjs` (IPC, migrations, log injection, etc.), `docs/`, `resources/`, `vite.config.ts`, `electron-builder.yml`, `package.json`.
+**Repo root (not exhaustive):** `.github/workflows/`, `scripts/check-*.mjs` (IPC, migrations, log injection, etc.), `docs/`, `resources/`, `vite.config.mts`, `electron-builder.yml`, `package.json`.
 
 ## Process boundaries
 
diff --git a/docs/development-environment.md b/docs/development-environment.md
index 7d8629a31..f0d9aa59d 100644
--- a/docs/development-environment.md
+++ b/docs/development-environment.md
@@ -519,7 +519,7 @@ Not installed by pnpm (install separately when needed):
 
 #### Vitest projects and worker allocation
 
-`vitest.config.ts` defines three projects:
+`vitest.config.mts` defines three projects:
 
 | Project          | Environment | Role                                    |
 | ---------------- | ----------- | --------------------------------------- |
@@ -527,7 +527,7 @@ Not installed by pnpm (install separately when needed):
 | `renderer-logic` | node        | Pure renderer unit tests (no setup)     |
 | `main`           | node        | Main, shared, preload, and script tests |
 
-Worker counts are derived in [`vitest.harness.ts`](../vitest.harness.ts) via `computeVitestMaxWorkers(cpuCount, ratio)`: jsdom workers use `RENDERER_UI_CPU_RATIO` because they are memory-heavy; node workers use `NODE_WORKER_CPU_RATIO`. Both pools floor at `MIN_VITEST_WORKERS` (currently 2) and cap effective CPU count at `MAX_VITEST_CPU_COUNT` (32). When tuning worker allocation, change those constants in the harness (not this doc). Shared Vite dependency inline lists (`VITEST_CORE_DEPS`, `VITEST_SERVER_INLINE_DEPS`) also live there — add new deps to the harness when tests need them inlined.
+Worker counts are derived in [`vitest.harness.mts`](../vitest.harness.mts) via `computeVitestMaxWorkers(cpuCount, ratio)`: jsdom workers use `RENDERER_UI_CPU_RATIO` because they are memory-heavy; node workers use `NODE_WORKER_CPU_RATIO`. Both pools floor at `MIN_VITEST_WORKERS` (currently 2) and cap effective CPU count at `MAX_VITEST_CPU_COUNT` (32). When tuning worker allocation, change those constants in the harness (not this doc). Shared Vite dependency inline lists (`VITEST_CORE_DEPS`, `VITEST_SERVER_INLINE_DEPS`) also live there — add new deps to the harness when tests need them inlined.
 
 By default all three Vitest projects run in **parallel** (`groupOrder: 0`). On memory-constrained hosts, set `VITEST_SEQUENTIAL_PROJECTS=1` to run `renderer-ui` first, then `renderer-logic` + `main` together (legacy behavior).
 
diff --git a/eslint.config.mjs b/eslint.config.mjs
index d861a059c..f8ca22cde 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -22,8 +22,8 @@ export default tseslint.config(
       'eslint.config.mjs',
       '**/*.d.ts',
       'eslint.config.*',
-      'vitest.config.ts',
-      'vite.config.ts',
+      'vitest.config.mts',
+      'vite.config.mts',
       '*.config.{ts,js,mjs,cjs}',
       'dist-electron/**',
       'coverage/**',
diff --git a/package.json b/package.json
index 179e125db..8ea109675 100644
--- a/package.json
+++ b/package.json
@@ -202,6 +202,7 @@
     "eslint-plugin-react-hooks": "^7.1.1",
     "eslint-plugin-security": "^4.0.1",
     "eslint-plugin-simple-import-sort": "^13.0.0",
+    "fake-indexeddb": "^6.2.5",
     "jsdom": "^29.1.1",
     "leaflet": "^1.9.4",
     "license-checker-rseidelsohn": "^4.4.2",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 422c9fa12..7535e93d9 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -231,6 +231,9 @@ importers:
       eslint-plugin-simple-import-sort:
         specifier: ^13.0.0
         version: 13.0.0(eslint@10.8.0(jiti@2.7.0)(supports-color@8.1.1))
+      fake-indexeddb:
+        specifier: ^6.2.5
+        version: 6.2.5
       jsdom:
         specifier: ^29.1.1
         version: 29.1.1(@noble/hashes@2.2.0)
@@ -2345,6 +2348,10 @@ packages:
   exponential-backoff@3.1.3:
     resolution: {integrity: sha512-ZgEeZXj30q+I0EN+CbSSpIyPaJ5HVQD18Z1m+u1FXbAeT94mr1zw50q4q6jiiC447Nl/YTcIYSAftiGqetwXCA==}
 
+  fake-indexeddb@6.2.5:
+    resolution: {integrity: sha512-CGnyrvbhPlWYMngksqrSSUT1BAVP49dZocrHuK0SvtR0D5TMs5wP0o3j7jexDJW01KSadjBp1M/71o/KR3nD1w==}
+    engines: {node: '>=18'}
+
   fast-deep-equal@3.1.3:
     resolution: {integrity: sha512-f3qQ9oQy9j2AhBe/H9VC91wLmKBCCU/gDOnKNAYG5hswO7BLKj09Hc5HYNz9cGI++xlpDCIgDaitVs03ATR84Q==}
 
@@ -7034,6 +7041,8 @@ snapshots:
 
   exponential-backoff@3.1.3: {}
 
+  fake-indexeddb@6.2.5: {}
+
   fast-deep-equal@3.1.3: {}
 
   fast-diff@1.3.0: {}
diff --git a/scripts/precommit-tests.mjs b/scripts/precommit-tests.mjs
index 45af6b5e3..5c761052c 100644
--- a/scripts/precommit-tests.mjs
+++ b/scripts/precommit-tests.mjs
@@ -134,6 +134,7 @@ function isMainProjectPath(filePath) {
     p.startsWith('src/architecture/') ||
     p.startsWith('scripts/') ||
     p === 'vitest.harness.ts' ||
+    p === 'vitest.harness.mts' ||
     p === 'vitest.harness.test.ts'
   );
 }
diff --git a/scripts/precommit-tests.test.mjs b/scripts/precommit-tests.test.mjs
index db44fb808..24ccab2d7 100644
--- a/scripts/precommit-tests.test.mjs
+++ b/scripts/precommit-tests.test.mjs
@@ -16,7 +16,9 @@ import {
 describe('precommit-tests force-full', () => {
   it('detects vitest harness and lockfile', () => {
     expect(isForceFullSuitePath('vitest.harness.ts')).toBe(true);
+    expect(isForceFullSuitePath('vitest.harness.mts')).toBe(true);
     expect(isForceFullSuitePath('vitest.config.ts')).toBe(true);
+    expect(isForceFullSuitePath('vitest.config.mts')).toBe(true);
     expect(isForceFullSuitePath('package.json')).toBe(true);
     expect(isForceFullSuitePath('pnpm-lock.yaml')).toBe(true);
     expect(isForceFullSuitePath('src/renderer/vitest.setup.ts')).toBe(true);
@@ -159,7 +161,7 @@ describe('precommit-tests runPrecommitTests', () => {
 
 describe('precommit-tests shouldForceFullSuite', () => {
   it('is true when any force-full path is present', () => {
-    expect(shouldForceFullSuite(['src/main/index.ts', 'vitest.config.ts'])).toBe(true);
+    expect(shouldForceFullSuite(['src/main/index.ts', 'vitest.config.mts'])).toBe(true);
     expect(shouldForceFullSuite(['src/main/index.ts'])).toBe(false);
   });
 });
diff --git a/src/main/vite-config.contract.test.ts b/src/main/vite-config.contract.test.ts
index f63221818..4e0cba0c8 100644
--- a/src/main/vite-config.contract.test.ts
+++ b/src/main/vite-config.contract.test.ts
@@ -3,7 +3,7 @@ import { readFileSync } from 'fs';
 import { join } from 'path';
 import { describe, expect, it } from 'vitest';
 
-const VITE_CONFIG = readFileSync(join(__dirname, '../../vite.config.ts'), 'utf-8');
+const VITE_CONFIG = readFileSync(join(__dirname, '../../vite.config.mts'), 'utf-8');
 
 describe('vite build config', () => {
   it('disables source maps for production bundles', () => {
@@ -14,4 +14,9 @@ describe('vite build config', () => {
   it('sets chunk size warning limit for Electron renderer advisory threshold', () => {
     expect(VITE_CONFIG).toMatch(/chunkSizeWarningLimit:\s*1000/);
   });
+
+  it('uses import.meta.dirname for native ESM configLoader compatibility', () => {
+    expect(VITE_CONFIG).not.toMatch(/__dirname/);
+    expect(VITE_CONFIG).toMatch(/import\.meta\.dirname/);
+  });
 });
diff --git a/src/renderer/lib/protocols/meshcore/MeshCoreTransport.ipc-cleanup.test.ts b/src/renderer/lib/protocols/meshcore/MeshCoreTransport.ipc-cleanup.test.ts
index 58ca01e38..2517163fd 100644
--- a/src/renderer/lib/protocols/meshcore/MeshCoreTransport.ipc-cleanup.test.ts
+++ b/src/renderer/lib/protocols/meshcore/MeshCoreTransport.ipc-cleanup.test.ts
@@ -2,7 +2,7 @@
  * @vitest-environment jsdom
  *
  * Needs window.electronAPI; keep in renderer-logic via per-file jsdom rather than
- * listing in vitest.config.ts RENDERER_LOGIC_EXCLUDE (eslint-ignored config).
+ * listing in vitest.config.mts RENDERER_LOGIC_EXCLUDE (eslint-ignored config).
  */
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
diff --git a/src/renderer/vitest.setup.ts b/src/renderer/vitest.setup.ts
index 2f93742f6..c3aaa1cfc 100644
--- a/src/renderer/vitest.setup.ts
+++ b/src/renderer/vitest.setup.ts
@@ -1,5 +1,7 @@
 import '@testing-library/jest-dom';
 import 'vitest-axe/extend-expect';
+// emoji-picker-element (ChatPanel) opens IndexedDB; jsdom has none.
+import 'fake-indexeddb/auto';
 
 import { cleanup } from '@testing-library/react';
 import i18next from 'i18next';
@@ -11,6 +13,59 @@ import en from './locales/en/translation.json';
 import { createElectronAPIMock, resetElectronAPIOutboxMock } from './vitest.electronApiMock';
 
 expect.extend(matchers);
+
+// jsdom omits structuredClone; fake-indexeddb requires it (Node engines provide it).
+if (typeof globalThis.structuredClone === 'function') {
+  vi.stubGlobal('structuredClone', globalThis.structuredClone.bind(globalThis));
+}
+
+/** Empty DOMRect for jsdom Range / IntersectionObserver stubs. */
+function emptyDomRect(): DOMRect {
+  return {
+    x: 0,
+    y: 0,
+    width: 0,
+    height: 0,
+    top: 0,
+    right: 0,
+    bottom: 0,
+    left: 0,
+    toJSON() {
+      return this;
+    },
+  };
+}
+
+// emoji-picker-element uses IntersectionObserver after IndexedDB opens (jsdom has none).
+interface IntersectionObserverStubInstance {
+  root: null;
+  rootMargin: string;
+  thresholds: number[];
+  observe: ReturnType<typeof vi.fn>;
+  unobserve: ReturnType<typeof vi.fn>;
+  disconnect: ReturnType<typeof vi.fn>;
+  takeRecords: ReturnType<typeof vi.fn>;
+}
+vi.stubGlobal(
+  'IntersectionObserver',
+  vi.fn(function IntersectionObserverStub(this: IntersectionObserverStubInstance) {
+    this.root = null;
+    this.rootMargin = '';
+    this.thresholds = [];
+    this.observe = vi.fn();
+    this.unobserve = vi.fn();
+    this.disconnect = vi.fn();
+    this.takeRecords = vi.fn(() => []);
+  }),
+);
+
+// emoji-picker-element ZWJ checks call Range#getBoundingClientRect (incomplete in jsdom).
+if (typeof Range !== 'undefined' && typeof Range.prototype.getBoundingClientRect !== 'function') {
+  Range.prototype.getBoundingClientRect = emptyDomRect;
+}
+if (typeof Range !== 'undefined' && typeof Range.prototype.getClientRects !== 'function') {
+  Range.prototype.getClientRects = () => [] as unknown as DOMRectList;
+}
 afterEach(() => {
   cleanup();
   resetElectronAPIOutboxMock();
diff --git a/tsconfig.main.json b/tsconfig.main.json
index 291063037..abc30a82f 100644
--- a/tsconfig.main.json
+++ b/tsconfig.main.json
@@ -15,7 +15,9 @@
     "baseUrl": ".",
     "paths": {
       "@/*": ["src/*"]
-    }
+    },
+    "allowImportingTsExtensions": true,
+    "noEmit": true
   },
   "include": [
     "src/main/**/*",
@@ -23,7 +25,7 @@
     "src/shared/**/*",
     "src/architecture/**/*",
     "src/main/types/**/*",
-    "vitest.harness.ts",
+    "vitest.harness.mts",
     "vitest.harness.test.ts"
   ],
   "exclude": ["node_modules", "dist"]
diff --git a/vite.config.ts b/vite.config.mts
similarity index 79%
rename from vite.config.ts
rename to vite.config.mts
index 838c2fb51..7743aa3e7 100644
--- a/vite.config.ts
+++ b/vite.config.mts
@@ -7,7 +7,7 @@ import react from '@vitejs/plugin-react';
 /** Emscripten glue fetches `orlp-ed25519.wasm` relative to the page; it is not inlined by Vite. */
 const ORLP_WASM_NAME = 'orlp-ed25519.wasm';
 const ORLP_WASM_SRC = path.resolve(
-  __dirname,
+  import.meta.dirname,
   `node_modules/@michaelhart/meshcore-decoder/lib/${ORLP_WASM_NAME}`,
 );
 
@@ -37,9 +37,9 @@ function meshcoreOrlpWasmPlugin(): import('vite').Plugin {
       if (!existsSync(ORLP_WASM_SRC)) return;
       const buf = readFileSync(ORLP_WASM_SRC);
       // Next to index.html (relative URL "orlp-ed25519.wasm" from document)
-      writeFileSync(path.resolve(__dirname, 'dist/renderer', ORLP_WASM_NAME), buf);
+      writeFileSync(path.resolve(import.meta.dirname, 'dist/renderer', ORLP_WASM_NAME), buf);
       // Some Emscripten builds resolve WASM relative to the JS chunk in assets/
-      writeFileSync(path.resolve(__dirname, 'dist/renderer/assets', ORLP_WASM_NAME), buf);
+      writeFileSync(path.resolve(import.meta.dirname, 'dist/renderer/assets', ORLP_WASM_NAME), buf);
     },
   };
 }
@@ -68,10 +68,10 @@ export default defineConfig({
     // Electron's renderer already has process.type === "renderer"; this matches that.
     'process.type': JSON.stringify('renderer'),
   },
-  root: path.resolve(__dirname, 'src/renderer'),
+  root: path.resolve(import.meta.dirname, 'src/renderer'),
   base: './',
   build: {
-    outDir: path.resolve(__dirname, 'dist/renderer'),
+    outDir: path.resolve(import.meta.dirname, 'dist/renderer'),
     emptyOutDir: true,
     sourcemap: false,
     // Production: omit source maps (smaller bundle). For crash symbolication use
@@ -109,22 +109,22 @@ export default defineConfig({
   },
   resolve: {
     alias: {
-      '@': path.resolve(__dirname, 'src'),
+      '@': path.resolve(import.meta.dirname, 'src'),
       // Node built-ins imported by transitive deps (e.g. @meshtastic/core 2.6.7 via
       // @meshtastic/transport-web-serial). Listing them as rollup externals emits bare
       // `import "os"` etc. which the browser rejects. Redirect to renderer-safe stubs instead.
-      fs: path.resolve(__dirname, 'src/renderer/shims/node-fs-stub.ts'),
-      os: path.resolve(__dirname, 'src/renderer/shims/node-os-stub.ts'),
-      path: path.resolve(__dirname, 'src/renderer/shims/node-path-stub.ts'),
-      util: path.resolve(__dirname, 'src/renderer/shims/node-util-stub.ts'),
-      stream: path.resolve(__dirname, 'src/renderer/shims/node-stream-stub.ts'),
-      child_process: path.resolve(__dirname, 'src/renderer/shims/node-child-process-stub.ts'),
-      net: path.resolve(__dirname, 'src/renderer/shims/node-net-stub.ts'),
-      events: path.resolve(__dirname, 'src/renderer/shims/node-events-stub.ts'),
+      fs: path.resolve(import.meta.dirname, 'src/renderer/shims/node-fs-stub.ts'),
+      os: path.resolve(import.meta.dirname, 'src/renderer/shims/node-os-stub.ts'),
+      path: path.resolve(import.meta.dirname, 'src/renderer/shims/node-path-stub.ts'),
+      util: path.resolve(import.meta.dirname, 'src/renderer/shims/node-util-stub.ts'),
+      stream: path.resolve(import.meta.dirname, 'src/renderer/shims/node-stream-stub.ts'),
+      child_process: path.resolve(import.meta.dirname, 'src/renderer/shims/node-child-process-stub.ts'),
+      net: path.resolve(import.meta.dirname, 'src/renderer/shims/node-net-stub.ts'),
+      events: path.resolve(import.meta.dirname, 'src/renderer/shims/node-events-stub.ts'),
     },
   },
   css: {
-    postcss: path.resolve(__dirname, 'postcss.config.cjs'),
+    postcss: path.resolve(import.meta.dirname, 'postcss.config.cjs'),
   },
   server: {
     port: 5173,
diff --git a/vitest.config.ts b/vitest.config.mts
similarity index 96%
rename from vitest.config.ts
rename to vitest.config.mts
index 51bb77dba..ab26b0bd3 100644
--- a/vitest.config.ts
+++ b/vitest.config.mts
@@ -1,7 +1,6 @@
 import { readdirSync } from 'node:fs';
 import os from 'node:os';
-import { dirname, join, relative, resolve } from 'node:path';
-import { fileURLToPath } from 'node:url';
+import { join, relative, resolve } from 'node:path';
 
 import react from '@vitejs/plugin-react';
 import { defineConfig } from 'vitest/config';
@@ -11,10 +10,9 @@ import {
   resolveVitestProjectMaxWorkers,
   VITEST_CORE_DEPS,
   VITEST_SERVER_INLINE_DEPS,
-} from './vitest.harness';
+} from './vitest.harness.mts';
 
-const __dirname = dirname(fileURLToPath(import.meta.url));
-const srcAlias = { '@': resolve(__dirname, 'src') };
+const srcAlias = { '@': resolve(import.meta.dirname, 'src') };
 const cpuCount = os.cpus().length;
 
 /** Per-project CI shards skip global thresholds; merge job enforces them on combined coverage. */
@@ -179,7 +177,7 @@ const RENDERER_LOGIC_LIB_UI_FALLBACK = new Set(
 );
 
 function collectRendererLibTestFiles(): string[] {
-  const libRoot = join(__dirname, 'src/renderer/lib');
+  const libRoot = join(import.meta.dirname, 'src/renderer/lib');
   const results: string[] = [];
   const walk = (dir: string): void => {
     for (const ent of readdirSync(dir, { withFileTypes: true })) {
@@ -187,7 +185,7 @@ function collectRendererLibTestFiles(): string[] {
       if (ent.isDirectory()) {
         walk(path);
       } else if (ent.name.endsWith('.test.ts')) {
-        results.push(relative(__dirname, path).split('\\').join('/'));
+        results.push(relative(import.meta.dirname, path).split('\\').join('/'));
       }
     }
   };
@@ -235,7 +233,7 @@ export default defineConfig({
           name: 'renderer-ui',
           globals: true,
           environment: 'jsdom',
-          setupFiles: [resolve(__dirname, 'src/renderer/vitest.setup.ts')],
+          setupFiles: [resolve(import.meta.dirname, 'src/renderer/vitest.setup.ts')],
           include: ['src/renderer/**/*.test.{ts,tsx}'],
           exclude: RENDERER_UI_EXCLUDE,
           pool: 'forks',
diff --git a/vitest.harness.ts b/vitest.harness.mts
similarity index 100%
rename from vitest.harness.ts
rename to vitest.harness.mts
diff --git a/vitest.harness.test.ts b/vitest.harness.test.ts
index 8e87abec5..f8954be40 100644
--- a/vitest.harness.test.ts
+++ b/vitest.harness.test.ts
@@ -10,7 +10,7 @@ import {
   resolveVitestProjectMaxWorkers,
   VITEST_CORE_DEPS,
   VITEST_SERVER_INLINE_DEPS,
-} from './vitest.harness';
+} from './vitest.harness.mts';
 
 describe('vitest.harness', () => {
   it('computeVitestMaxWorkers applies ratio and MIN_VITEST_WORKERS floor', () => {