fix(reference-source): recognize Kotlin files in imported inventories

Classify .kt and .kts at the source owner so imported entries and historical language summaries preserve Kotlin identity.

Validation: production inventory projection covers Kotlin, Gradle script, Java and backup-suffix controls.

Based on #3224.

Co-authored-by: Aurantium <280805072+Aurantium-47@users.noreply.github.com>

src/application/ReferenceSourceImportEntries.test.ts

@@ -0,0 +1,60 @@
+import { createHash } from "node:crypto";
+
+import { expect, it } from "vitest";
+
+import { parseReferenceSourceEntries } from "./ReferenceSourceImportEntries.js";
+import { historicalSourceLanguages } from "../domain/referenceSourceGraph.js";
+import type { ReferenceSourceRead } from "../reference/ReferenceSourceReaderTypes.js";
+
+it("retains Kotlin source identity and language across the inventory projection", () => {
+  const files = [
+    [
+      "MainActivity.kt",
+      "import android.app.Activity\nclass MainActivity : Activity()\n",
+      ["source"],
+      "Kotlin",
+    ],
+    ["task.kts", 'println("hello")\n', ["source"], "Kotlin"],
+    [
+      "build.gradle.kts",
+      'plugins { kotlin("jvm") version "2.3.0" }\n',
+      ["manifest", "source"],
+      "Kotlin",
+    ],
+    ["MainActivity.kt.backup", "backup\n", ["unknown"], null],
+    ["Legacy.java", "class Legacy {}\n", ["source"], "Java"],
+  ] as const;
+  const read: ReferenceSourceRead = {
+    root: "/selected/source",
+    entries: files.map(([path, content]) => ({
+      status: "read",
+      kind: "file",
+      path,
+      bytes: Buffer.from(content),
+      size: Buffer.byteLength(content),
+    })),
+    bytesRead: files.reduce(
+      (sum, [, content]) => sum + Buffer.byteLength(content),
+      0,
+    ),
+    limitations: [],
+  };
+  const parsed = parseReferenceSourceEntries(
+    read,
+    new Set(files.map(([path]) => path)),
+  );
+  for (const [path, content, classifications, language] of files)
+    expect(parsed.entries).toContainEqual({
+      path,
+      kind: "file",
+      language,
+      classifications,
+      size: Buffer.byteLength(content),
+      sha256: createHash("sha256").update(content).digest("hex"),
+      content_state: "hashed",
+      limitations: [],
+    });
+  expect(historicalSourceLanguages(parsed.entries)).toEqual(["Java", "Kotlin"]);
+  expect(parsed.parseFailures).toEqual([]);
+  expect(parsed.relationships).toEqual([]);
+});

src/domain/referenceSourceClassification.ts

@@ -27,6 +27,8 @@ const CODE_EXTENSIONS = new Set([
   "rs",
   "go",
   "java",
+  "kt",
+  "kts",
   "c",
   "h",
   "cpp",
@@ -54,6 +56,8 @@ const LANGUAGE_BY_EXTENSION = new Map<string, string>([
   ["rs", "Rust"],
   ["go", "Go"],
   ["java", "Java"],
+  ["kt", "Kotlin"],
+  ["kts", "Kotlin"],
   ["c", "C"],
   ["h", "C"],
   ["cpp", "C++"],