fix: handle unobfuscated Minecraft versions (26.1+)

__tests__/core/remap-service.test.ts

@@ -374,4 +374,32 @@ describe('JAR Remapping', () => {
       expect(intermediaryFieldCount).toBeLessThan(20);
     }, 60000);
   });
+
+  describe('Unobfuscated version handling', () => {
+    // 26.1+ snapshots ship without obfuscation — no intermediary or Yarn mappings exist.
+    const UNOBFUSCATED_VERSION = '26.1-snapshot-8';
+
+    it('should throw a clear error when requesting yarn mappings for an unobfuscated version', async () => {
+      const remapService = getRemapService();
+      await expect(remapService.getRemappedJar(UNOBFUSCATED_VERSION, 'yarn')).rejects.toThrow(
+        /yarn mappings are not supported for unobfuscated/i,
+      );
+    }, 60000); // includes client JAR download on first run
+
+    it('should throw a clear error when requesting intermediary mappings for an unobfuscated version', async () => {
+      const remapService = getRemapService();
+      await expect(
+        remapService.getRemappedJar(UNOBFUSCATED_VERSION, 'intermediary'),
+      ).rejects.toThrow(/intermediary mappings are not supported for unobfuscated/i);
+    }, 60000);
+
+    it('should return the raw client JAR for mojmap on an unobfuscated version', async () => {
+      const remapService = getRemapService();
+      const jarPath = await remapService.getRemappedJar(UNOBFUSCATED_VERSION, 'mojmap');
+      expect(jarPath).toBeDefined();
+      expect(existsSync(jarPath)).toBe(true);
+      // The returned path is the raw client JAR, not a remapped copy
+      expect(jarPath).not.toContain('remapped');
+    }, 60000);
+  });
 });

__tests__/core/version-manager.test.ts

@@ -36,4 +36,20 @@ describe('Version Management', () => {
 
     expect(exists).toBe(false);
   }, 30000);
+
+  describe('Unobfuscated version detection', () => {
+    it('should return false for obfuscated versions', async () => {
+      const versionManager = getVersionManager();
+      // TEST_VERSION (1.21.11) is an obfuscated release — client_mappings present
+      const result = await versionManager.isVersionUnobfuscated(TEST_VERSION);
+      expect(result).toBe(false);
+    }, 30000);
+
+    it('should return true for unobfuscated versions (26.1+)', async () => {
+      const versionManager = getVersionManager();
+      // 26.1 snapshots ship without obfuscation — no client_mappings in version JSON
+      const result = await versionManager.isVersionUnobfuscated('26.1-snapshot-8');
+      expect(result).toBe(true);
+    }, 30000);
+  });
 });

src/services/remap-service.ts

@@ -72,6 +72,20 @@ export class RemapService {
       }
     });
 
+    // Minecraft 26.1+ ships unobfuscated JARs — no remapping is possible or needed.
+    const isUnobfuscated = await this.versionManager.isVersionUnobfuscated(version);
+    if (isUnobfuscated) {
+      if (mapping !== 'mojmap') {
+        throw new Error(
+          `${mapping} mappings are not supported for unobfuscated Minecraft versions. ` +
+            `Version ${version} ships without obfuscation — use 'mojmap' mapping instead.`,
+        );
+      }
+      // The raw JAR is already in Mojang's human-readable names; decompile it directly.
+      logger.info(`Version ${version} is unobfuscated — skipping remapping (mojmap)`);
+      return inputJar;
+    }
+
     // Yarn mappings require two-step remapping: official -> intermediary -> named
     if (mapping === 'yarn') {
       return await this.remapYarn(version, inputJar, outputPath, onProgress);

src/services/version-manager.ts

@@ -142,6 +142,18 @@ export class VersionManager {
     }
   }
 
+  /**
+   * Check if a Minecraft version ships an unobfuscated JAR.
+   *
+   * Starting with Minecraft 26.1 snapshots, Mojang stopped obfuscating the
+   * client JAR. These versions have no `client_mappings` entry in their
+   * version JSON because there is nothing to reverse-map.
+   */
+  async isVersionUnobfuscated(version: string): Promise<boolean> {
+    const versionJson = await this.downloader.getVersionJson(version);
+    return !versionJson.downloads.client_mappings;
+  }
+
   /**
    * Get version JAR path (must be cached)
    */