diff --git a/.agents/memory/lit-analyzer-ts6.md b/.agents/memory/lit-analyzer-ts6.md
index ebbb795..abfae86 100644
--- a/.agents/memory/lit-analyzer-ts6.md
+++ b/.agents/memory/lit-analyzer-ts6.md
@@ -31,7 +31,7 @@ registerHooks({
 - Node runs the `.ts` script directly (type stripping), so no build step.
 - Import the package entry, or spawn the package's bin with
   `node:child_process`, rather than `await import("lit-analyzer/cli.js")`.
-  `project/no-asset-imports` allows `.js` subpaths, but the CLI file runs on
+  `project/no-asset-imports` allows `.js` (and `.mts`/`.mjs`) subpaths, but the CLI file runs on
   import and bypasses the package's public entry.
 - CI runs `npm run lit-check` as its own step.
 - It is tooling under `scripts/`: no tests; a narrow `overrides` entry for it
diff --git a/.agents/memory/ts-only-files-and-imports.md b/.agents/memory/ts-only-files-and-imports.md
index 8ac48f8..f488cd1 100644
--- a/.agents/memory/ts-only-files-and-imports.md
+++ b/.agents/memory/ts-only-files-and-imports.md
@@ -1,5 +1,5 @@
 ---
-description: Every file is .ts (no js/mjs/cjs/jsx/tsx, configs included); imports name only .ts files or .js package subpaths; CSS comes from HTML, JSON/SVG become .ts modules
+description: Every file is .ts (no js/mjs/cjs/jsx/tsx, configs included); imports name only .ts files or .js/.mts/.mjs package subpaths; CSS comes from HTML, JSON/SVG become .ts modules
 ---
 
 The user's rule, from the Deno days and restated for Node (2026-10-12): "No
@@ -12,19 +12,22 @@ plain `.ts`. Build output in a gitignored folder is the only JS.
 `noUncheckedIndexedAccess`). If a tool or framework seems to need a JS or TSX
 file, stop and flag it instead of adding one.
 
-## No asset imports (2026-10-14, widened 2026-10-16)
+## No asset imports (2026-10-14, widened 2026-10-16 and 2026-10-17)
 
-`.ts` and `.js` imports are allowed: our own files stay `.ts`, and `.js`
-covers package subpaths such as `lit/decorators.js`.
-`project/no-asset-imports` (in `scripts/project-lint.ts`) fails:
+`project/no-asset-imports` (in `scripts/project-lint.ts`; it was
+`no-non-ts-imports` before 2026-10-16) fails:
 
 - a relative, absolute, `#`, or package-subpath specifier whose last segment
-  has any other extension: `.css`, `.json`, `.svg`, `.mjs`, `.tsx`;
+  has an extension other than `.ts`, `.js`, `.mts`, or `.mjs`: `.css`,
+  `.json`, `.svg`, `.jsx`, `.tsx`, and every other asset;
 - any `?query` suffix (`?raw`, `?url`, `?inline`);
 - any import attributes (`with { type: "json" }`, `with { type: "text" }`).
 
-Bare packages (`lit`, `@types/json-schema`, `lodash.debounce`), `#` aliases,
-and `node:` builtins pass. `@fortawesome/x/svgs/a.svg` fails.
+`.js`, `.mts`, and `.mjs` are allowed (user decision, 2026-10-17) for package
+subpaths such as `lit/decorators.js` or `pdfjs-dist/legacy/build/pdf.mjs`;
+our own files are still `.ts` only. `.jsx` and `.tsx` stay banned. Bare
+packages (`lit`, `@types/json-schema`, `lodash.debounce`), `#` aliases, and
+`node:` builtins pass. `@fortawesome/x/svgs/a.svg` fails.
 
 ```ts
 import "./theme.css"; // no
diff --git a/scripts/project-lint.ts b/scripts/project-lint.ts
index 663997e..13da199 100644
--- a/scripts/project-lint.ts
+++ b/scripts/project-lint.ts
@@ -70,14 +70,18 @@ const noDisableCommentsRule: ProjectRule = {
 /** A module specifier read as a path: relative, absolute, or a `#` alias. */
 const PATH_SPECIFIER_PATTERN: RegExp = /^[./#]/u;
 
-/** Script module extensions an import may name: our `.ts` files and `.js` package subpaths. */
-const SCRIPT_EXTENSIONS: readonly string[] = [".ts", ".js"];
+/**
+ * Script module extensions an import may name: our `.ts` files and `.js`,
+ * `.mts`, or `.mjs` package subpaths. `.cts`, `.cjs`, `.tsx`, and `.jsx` are
+ * not among them.
+ */
+const SCRIPT_EXTENSIONS: ReadonlySet<string> = new Set([".ts", ".js", ".mts", ".mjs"]);
 
 /**
  * Whether `source` names an asset rather than a script module: a query string
- * such as `?raw`, or a final path segment with an extension other than `.ts`
- * or `.js`. Bare package names are left alone, dots and all, as are
- * extensionless paths.
+ * such as `?raw`, or a final path segment whose extension, from its last dot,
+ * is not `.ts`, `.js`, `.mts`, or `.mjs`. Bare package names are left alone,
+ * dots and all, as are extensionless paths.
  */
 function isAssetSource(source: string): boolean {
   if (source.includes("?")) {
@@ -94,25 +98,28 @@ function isAssetSource(source: string): boolean {
   if (lastSegment === "." || lastSegment === ".." || !lastSegment.includes(".")) {
     return false;
   }
-  return !SCRIPT_EXTENSIONS.some((extension: string): boolean => lastSegment.endsWith(extension));
+  const extension: string = lastSegment.slice(lastSegment.lastIndexOf("."));
+  return !SCRIPT_EXTENSIONS.has(extension);
 }
 
 /**
  * `no-asset-imports` — rejects importing anything but a script module: a
  * source path, static or a dynamic `import()` with a string literal, ending in
- * an extension other than `.ts` or `.js` (`.css`, `.json`, `.svg`, `.tsx`) or
- * carrying a query string (`?raw`, `?url`), and any import or export with
- * import attributes. `.js` covers package subpaths such as
- * `lit/decorators.js`. Bare package names, `#` aliases, and `node:` builtins
+ * an extension other than `.ts`, `.js`, `.mts`, or `.mjs` (`.css`, `.json`,
+ * `.svg`, `.jsx`, `.tsx`, `.cjs`) or carrying a query string (`?raw`, `?url`),
+ * and any import or export with import attributes. `.js`, `.mts`, and `.mjs`
+ * cover package subpaths such as `lit/decorators.js` or
+ * `pdfjs-dist/legacy/build/pdf.mjs`; our own files are still `.ts` only. Bare
+ * package names, `#` aliases, and `node:` builtins
  * without an extension pass; package subpaths are checked like paths.
  */
 const noAssetImportsRule: ProjectRule = {
   meta: {
     type: "problem",
-    docs: { description: "Disallow importing assets instead of .ts or .js modules" },
+    docs: { description: "Disallow importing assets instead of .ts, .js, .mts, or .mjs modules" },
     schema: [],
     messages: {
-      extension: "Only .ts and .js modules may be imported.",
+      extension: "Only .ts, .js, .mts and .mjs modules may be imported.",
       attributes: "Import attributes are not allowed.",
     },
   },