diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 274992cd..0db12e3a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -77,3 +77,39 @@ jobs:
 
       - name: Exercise every breadth grammar
         run: node --import tsx --test test/generic-node24.test.ts
+
+  windows-node26-install:
+    name: Windows Node 26 install regression
+    runs-on: windows-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          persist-credentials: false
+
+      - name: Setup Node.js
+        uses: actions/setup-node@820762786026740c76f36085b0efc47a31fe5020 # v7.0.0
+        with:
+          node-version: '26'
+          cache: npm
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build
+        run: npm run build
+
+      - name: Test
+        run: npm test
+
+      - name: Pack and install the published artifact shape
+        shell: pwsh
+        run: |
+          $tarball = (npm pack --json | ConvertFrom-Json)[0].filename
+          $consumer = Join-Path $env:RUNNER_TEMP 'graft-packed-install'
+          New-Item -ItemType Directory -Force -Path $consumer | Out-Null
+          Push-Location $consumer
+          npm init --yes
+          npm install (Join-Path $env:GITHUB_WORKSPACE $tarball)
+          npx graft --version
+          Pop-Location
diff --git a/README.md b/README.md
index 68a6a061..dd902334 100644
--- a/README.md
+++ b/README.md
@@ -486,7 +486,12 @@ compiler-grade layer, all `$0` and deterministic (no model, no key):
   `library()`/`source()` imports), and **Vue** single-file components (their
   `<script>` blocks go through the TypeScript extractor).
 
-- **Broad**: symbols (functions, classes, methods, types, …) plus name-resolved
+  Kotlin's native parser is an optional install so a platform without a compatible
+  native build can still install and use Graft. If it is unavailable, a build that
+  encounters `.kt` or `.kts` files prints one warning and skips only those files;
+  every other supported language remains indexed.
+
+- **Broad** — symbols (functions, classes, methods, types, …) plus name-resolved
   call edges via a generic tree-sitter extractor, one grammar per language:
   **Rust, C, C++, C#, Ruby, Scala, Elixir, Solidity,
   Dart, Clojure, Nix, Lua**, and **OCaml, Zig** (symbols only for now, no call edges).
diff --git a/package-lock.json b/package-lock.json
index 53f20592..06067726 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -18,7 +18,6 @@
         "tree-sitter": "^0.21.1",
         "tree-sitter-go": "^0.23.4",
         "tree-sitter-java": "^0.23.5",
-        "tree-sitter-kotlin": "^0.3.8",
         "tree-sitter-php": "^0.23.4",
         "tree-sitter-python": "^0.21.0",
         "tree-sitter-r": "npm:@davisvaughan/tree-sitter-r@^1.3.0",
@@ -43,6 +42,9 @@
       },
       "engines": {
         "node": ">=20"
+      },
+      "optionalDependencies": {
+        "tree-sitter-kotlin": "^0.3.8"
       }
     },
     "node_modules/@anthropic-ai/sdk": {
@@ -1163,6 +1165,7 @@
       "integrity": "sha512-A4obq6bjzmYrA+F0JLLoheFPcofFkctNaZSpnDd+GPn1SfVZLY4/GG4C0cYVBTOShuPBGGAOPLM1JWLZQV4m1g==",
       "hasInstallScript": true,
       "license": "MIT",
+      "optional": true,
       "dependencies": {
         "node-addon-api": "^7.1.0",
         "node-gyp-build": "^4.8.0"
@@ -1180,7 +1183,8 @@
       "version": "7.1.1",
       "resolved": "https://registry.npmjs.org/node-addon-api/-/node-addon-api-7.1.1.tgz",
       "integrity": "sha512-5m3bsyrjFWE1xf7nz7YXdN4udnVtXK6/Yfgn5qnahL6bCkf2yKt4k3nuTKAtT4r3IG8JNR2ncsIMdZuAzJjHQQ==",
-      "license": "MIT"
+      "license": "MIT",
+      "optional": true
     },
     "node_modules/tree-sitter-php": {
       "version": "0.23.12",
diff --git a/package.json b/package.json
index bbd74d8c..c8c3a290 100644
--- a/package.json
+++ b/package.json
@@ -63,7 +63,6 @@
     "tree-sitter": "^0.21.1",
     "tree-sitter-go": "^0.23.4",
     "tree-sitter-java": "^0.23.5",
-    "tree-sitter-kotlin": "^0.3.8",
     "tree-sitter-php": "^0.23.4",
     "tree-sitter-python": "^0.21.0",
     "tree-sitter-r": "npm:@davisvaughan/tree-sitter-r@^1.3.0",
@@ -74,6 +73,9 @@
     "vscode-languageserver-protocol": "^3.18.2",
     "web-tree-sitter": "^0.26.13"
   },
+  "optionalDependencies": {
+    "tree-sitter-kotlin": "^0.3.8"
+  },
   "devDependencies": {
     "@types/d3-force": "^3.0.10",
     "@types/node": "^26.1.0",
diff --git a/src/graph/build.ts b/src/graph/build.ts
index 178f7f58..14612d1a 100644
--- a/src/graph/build.ts
+++ b/src/graph/build.ts
@@ -17,10 +17,15 @@ import { readFileSync } from "node:fs";
 import { basename, dirname, resolve } from "node:path";
 import { walkDir } from "../ingest/fs.js";
 import { contextDirFor, ensureGitignored, ensureSearchable } from "../context/node-file.js";
-import { extractFile, languageLabelOf, languageOf, type Language, type RawEdge } from "./extract.js";
-import { extractGeneric, fallbackLangOf, genericLangOf, warmGenericGrammars, type GenericLang } from "./generic.js";
-import { containerLangOf, extractContainer, warmContainerGrammars, type ContainerLang } from "./container.js";
-import { missingNativePackages, nativeReady, type NativeFallback } from "./native.js";
+import {
+  extractFile,
+  kotlinParserUnavailableMessage,
+  languageLabelOf,
+  languageOf,
+  type RawEdge,
+} from "./extract.js";
+import { extractGeneric, genericLangOf, warmGenericGrammars } from "./generic.js";
+import { containerLangOf, extractContainer, warmContainerGrammars } from "./container.js";
 import { contentHash } from "../util/id.js";
 import { relPosix } from "../util/paths.js";
 import { readSourceFile } from "../util/source.js";
@@ -226,6 +231,13 @@ export async function buildGraph(
    * javascript, or the banner claims a repo's JavaScript went unindexed. */
   const langs = new Set<string>();
   const errors: string[] = [];
+  // Kotlin is the only optional depth-tier grammar. Probe it once, and only when
+  // the repository actually contains Kotlin, so a failed native install cannot
+  // affect a TypeScript/JavaScript-only build or produce startup noise.
+  const kotlinUnavailable = files.some((f) => languageOf(f.abs) === "kotlin")
+    ? kotlinParserUnavailableMessage()
+    : null;
+  if (kotlinUnavailable) errors.push(kotlinUnavailable);
 
   // In a git worktree there is nothing to reuse *yet* — `graft/` is gitignored, so
   // git never checked it out — but the parent checkout's graph is one directory away.
@@ -303,7 +315,14 @@ export async function buildGraph(
     }
 
     const hash = contentHash(source);
-    if (cached && hash === cached.hash && cached.via === via) {
+    if (lang === "kotlin" && kotlinUnavailable) {
+      // Keep the source fingerprint current, but don't cache this as a parse
+      // failure: a later install may make the optional addon available.
+      entries[rel] = { size: f.size, mtimeMs: f.mtimeMs, hash, nodes: [], rawEdges: [], skipped: true };
+      return;
+    }
+
+    if (cached && hash === cached.hash && !cached.skipped) {
       entries[rel] = { ...cached, size: f.size, mtimeMs: f.mtimeMs };
       sources.set(rel, source);
       reused++;
diff --git a/src/graph/check.ts b/src/graph/check.ts
index c503f00b..3e4e3245 100644
--- a/src/graph/check.ts
+++ b/src/graph/check.ts
@@ -20,10 +20,10 @@
 import { resolve } from "node:path";
 import { relPosix } from "../util/paths.js";
 import { contextDirFor } from "../context/node-file.js";
-import { extractFile } from "./extract.js";
-import { extractGeneric } from "./generic.js";
-import { extractContainer } from "./container.js";
-import { listSourceFiles, tierOf, warmGrammarsFor } from "./build.js";
+import { extractFile, kotlinParserUnavailableMessage, languageOf } from "./extract.js";
+import { extractGeneric, genericLangOf, warmGenericGrammars } from "./generic.js";
+import { containerLangOf, extractContainer, warmContainerGrammars } from "./container.js";
+import { listSourceFiles } from "./build.js";
 import { readGraph, wiringPath } from "./write.js";
 import { readFingerprint } from "./fingerprint.js";
 import { readSourceFile } from "../util/source.js";
@@ -88,6 +88,12 @@ export async function checkGraph(
   const fpOnlyDirs = readFingerprint(outDir)?.onlyDirs;
   const onlyDirs = fpOnlyDirs && fpOnlyDirs.length > 0 ? new Set(fpOnlyDirs) : undefined;
   const sourceFiles = listSourceFiles(root, outDir, undefined, onlyDirs);
+  const kotlinUnavailable = sourceFiles.some((file) => languageOf(file) === "kotlin")
+    ? kotlinParserUnavailableMessage()
+    : null;
+  await warmGenericGrammars(
+    new Set(sourceFiles.map((f) => genericLangOf(f)?.name).filter((n): n is string => !!n)),
+  );
   // Container-tier grammars need the same warmup as the generic ones, for the same
   // reason: extraction below is synchronous. Missing that is what made `graft
   // check` report every `.vue` node as `removed` right after a clean build (#236)
@@ -97,10 +103,14 @@ export async function checkGraph(
   await warmGrammarsFor(sourceFiles);
   const current = new Map<string, string>(); // id → body_hash
   for (const file of sourceFiles) {
-    // The same dispatch `buildGraph` uses (`tierOf`). The two must stay in step: a
-    // tier the build extracts and the check cannot see reports as `removed`
-    // forever, and the `graft build` the check tells you to run can never repair it.
-    const { lang, container, generic } = tierOf(file);
+    // The same three-way branch `buildGraph` uses, in the same order. The two must
+    // stay in step: a tier the build extracts and the check cannot see reports as
+    // `removed` forever, and the `graft build` the check tells you to run can never
+    // repair it.
+    const lang = languageOf(file);
+    if (lang === "kotlin" && kotlinUnavailable) continue;
+    const container = lang ? null : containerLangOf(file);
+    const generic = lang || container ? null : genericLangOf(file);
     let source: string | null;
     try {
       source = readSourceFile(file);
@@ -133,6 +143,9 @@ export async function checkGraph(
   const committedById = new Map(committed.nodes.map((n) => [n.id, n]));
   result.nodes = committedById.size;
   for (const [id, node] of committedById) {
+    // Do not call a graph stale merely because an optional parser isn't installed
+    // in this environment. The next build will give the actionable diagnostic.
+    if (kotlinUnavailable && languageOf(node.path) === "kotlin") continue;
     const now = current.get(id);
     if (now === undefined) result.removed.push(id);
     else if (now !== node.body_hash) result.changed.push(id);
diff --git a/src/graph/extract-cache.ts b/src/graph/extract-cache.ts
index db3ba22c..792e52a3 100644
--- a/src/graph/extract-cache.ts
+++ b/src/graph/extract-cache.ts
@@ -48,10 +48,9 @@ export interface ExtractEntry {
    * re-reports the same error and contributes no nodes, exactly as a cold build
    * would. */
   error?: string;
-  /** The breadth-tier grammar that parsed this file standing in for its depth-tier
-   * one, whose native grammar didn't load. Absent for every other file. The entry is
-   * replayed only while the same stand-in would parse it again. */
-  via?: string;
+  /** The optional parser for this file's language was unavailable. Unlike `error`,
+   * this entry is re-parsed if that parser becomes available on a later run. */
+  skipped?: true;
 }
 
 export interface ExtractCache {
diff --git a/src/graph/extract.ts b/src/graph/extract.ts
index a8215fa4..b5d62f64 100644
--- a/src/graph/extract.ts
+++ b/src/graph/extract.ts
@@ -6,9 +6,15 @@
  * arrow-function consts) plus unresolved edge intents. Edge *targets* are
  * resolved against the whole-repo node index later, in build.ts.
  */
-// Types only: the native grammars themselves load on first use, in native.ts, so
-// a missing binary costs its own language instead of every command.
-import type Parser from "tree-sitter";
+import Parser from "tree-sitter";
+import { createRequire } from "node:module";
+import TypeScript from "tree-sitter-typescript";
+import Python from "tree-sitter-python";
+import Go from "tree-sitter-go";
+import R from "tree-sitter-r";
+import Java from "tree-sitter-java";
+import Swift from "tree-sitter-swift";
+import PHP from "tree-sitter-php";
 import { basename } from "node:path";
 import { contentHash } from "../util/id.js";
 import { collectBindings, goReceiverVarOf, resolveRecvType, type FileBindings } from "./bindings.js";
@@ -305,6 +311,61 @@ const FUNCTION_VALUE_TYPES = new Set([
 
 const EMPTY_SET: ReadonlySet<string> = new Set();
 
+const parser = new Parser();
+const require = createRequire(import.meta.url);
+
+const GRAMMARS: Record<Exclude<Language, "kotlin">, unknown> = {
+  typescript: TypeScript.typescript,
+  tsx: TypeScript.tsx,
+  python: Python,
+  go: Go,
+  r: R,
+  java: Java,
+  swift: Swift,
+  php: PHP.php,
+};
+
+const KOTLIN_PARSER_UNAVAILABLE =
+  "Kotlin files were skipped because the optional tree-sitter-kotlin parser is unavailable. " +
+  "Reinstall @nanonets/graft in an environment where tree-sitter-kotlin can build to index .kt and .kts files.";
+
+let kotlinGrammar: unknown | null | undefined;
+let loadKotlinGrammar = (): unknown => require("tree-sitter-kotlin");
+
+/**
+ * Resolve the optional Kotlin native addon only when a Kotlin file is encountered.
+ * A missing or unloadable addon must never prevent another language from building.
+ */
+export function kotlinParserUnavailableMessage(): string | null {
+  if (kotlinGrammar === undefined) {
+    try {
+      kotlinGrammar = loadKotlinGrammar();
+    } catch {
+      kotlinGrammar = null;
+    }
+  }
+  return kotlinGrammar === null ? KOTLIN_PARSER_UNAVAILABLE : null;
+}
+
+/** Test seam for the optional native addon. Not part of Graft's package API. */
+export function swapKotlinGrammarLoaderForTest(loader: () => unknown): () => void {
+  const previousLoader = loadKotlinGrammar;
+  const previousGrammar = kotlinGrammar;
+  loadKotlinGrammar = loader;
+  kotlinGrammar = undefined;
+  return () => {
+    loadKotlinGrammar = previousLoader;
+    kotlinGrammar = previousGrammar;
+  };
+}
+
+function grammarFor(lang: Language): unknown {
+  if (lang !== "kotlin") return GRAMMARS[lang];
+  const unavailable = kotlinParserUnavailableMessage();
+  if (unavailable) throw new Error(unavailable);
+  return kotlinGrammar;
+}
+
 export interface WalkCtx {
   rel: string;
   source: string;
@@ -369,7 +430,8 @@ function parseSource(parser: Parser, source: string): Parser.SyntaxNode {
 /** Throws when `lang`'s native grammar is unavailable: callers check `nativeReady`
  * (native.ts) first and hand such a file to its breadth-tier stand-in instead. */
 export function extractFile(rel: string, source: string, lang: Language): ExtractResult {
-  const root = parseSource(nativeParser(lang), source);
+  parser.setLanguage(grammarFor(lang) as never);
+  const root = parseSource(source);
   const bindings = collectBindings(root, lang);
   const importedSymbols = collectImportedSymbols(root, lang);
   const rGenerics = lang === "r" ? collectRGenerics(root) : EMPTY_SET;
diff --git a/test/graph-languages.test.ts b/test/graph-languages.test.ts
index 6b28daea..d4edcd1d 100644
--- a/test/graph-languages.test.ts
+++ b/test/graph-languages.test.ts
@@ -17,7 +17,12 @@ import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { buildGraph } from "../src/graph/build.js";
 import { buildRepoMap } from "../src/graph/map.js";
-import { languageLabelOf, languageOf } from "../src/graph/extract.js";
+import {
+  kotlinParserUnavailableMessage,
+  languageLabelOf,
+  languageOf,
+  swapKotlinGrammarLoaderForTest,
+} from "../src/graph/extract.js";
 import { readGraph, wiringPath } from "../src/graph/write.js";
 
 /** Every extension graft claims to index, one per grammar/label pairing. */
@@ -92,7 +97,11 @@ test("the build banner and repo map report every language they indexed", async (
   writeFileSync(join(d, "src", "a.swift"), "func swiftOnly() -> Int {\n  return 1\n}\n");
 
   const r = await buildGraph(d);
-  assert.deepEqual(r.languages, ["javascript", "jsx", "kotlin", "python", "swift", "tsx", "typescript"]);
+  const kotlinAvailable = !r.errors.some((error) => error.startsWith("Kotlin files were skipped"));
+  assert.deepEqual(
+    r.languages,
+    ["javascript", "jsx", ...(kotlinAvailable ? ["kotlin"] : []), "python", "swift", "tsx", "typescript"],
+  );
 
   // The reported symbol was queryable all along — that mismatch is what the issue was
   // about, so pin both halves together.
@@ -105,3 +114,37 @@ test("the build banner and repo map report every language they indexed", async (
   // `map` derives labels from paths independently, so it gets its own assertion.
   assert.deepEqual(buildRepoMap(graph!).totals.languages, r.languages);
 });
+
+test("Kotlin is indexed when its optional parser is available", async (t) => {
+  if (kotlinParserUnavailableMessage()) {
+    t.skip("tree-sitter-kotlin is unavailable in this runtime");
+    return;
+  }
+  const dir = mkdtempSync(join(tmpdir(), "graft-kotlin-available-"));
+  writeFileSync(join(dir, "app.kt"), "fun indexedKotlin(): Int = 1\n");
+  const result = await buildGraph(dir, { reuse: false });
+  assert.deepEqual(result.errors, []);
+  assert.deepEqual(result.languages, ["kotlin"]);
+  const graph = readGraph(wiringPath(result.contextDir))!;
+  assert.ok(graph.nodes.some((node) => node.name === "indexedKotlin"), "Kotlin function is indexed");
+});
+
+test("a missing Kotlin parser skips Kotlin only and leaves TypeScript indexed", async () => {
+  const dir = mkdtempSync(join(tmpdir(), "graft-kotlin-optional-"));
+  writeFileSync(join(dir, "app.ts"), "export function stillIndexed() { return 1; }\n");
+  writeFileSync(join(dir, "app.kt"), "fun skippedKotlin(): Int = 1\n");
+  const restore = swapKotlinGrammarLoaderForTest(() => {
+    throw new Error("Cannot find module 'tree-sitter-kotlin'");
+  });
+  try {
+    const result = await buildGraph(dir, { reuse: false });
+    assert.equal(result.errors.length, 1, "one Kotlin availability warning");
+    assert.match(result.errors[0], /Kotlin files were skipped/);
+    assert.deepEqual(result.languages, ["typescript"]);
+    const graph = readGraph(wiringPath(result.contextDir))!;
+    assert.ok(graph.nodes.some((node) => node.name === "stillIndexed"), "TypeScript remains indexed");
+    assert.ok(!graph.nodes.some((node) => node.path === "app.kt"), "Kotlin contributes no partial nodes");
+  } finally {
+    restore();
+  }
+});