diff --git a/package-lock.json b/package-lock.json
index 08ce22f..694d8ec 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "source-doc",
-  "version": "0.2.1",
+  "version": "0.3.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "source-doc",
-      "version": "0.2.1",
+      "version": "0.3.0",
       "license": "MIT",
       "devDependencies": {
         "@types/glob": "^8.1.0",
diff --git a/src/codeLensProvider.ts b/src/codeLensProvider.ts
index 9a64e84..54c59f1 100644
--- a/src/codeLensProvider.ts
+++ b/src/codeLensProvider.ts
@@ -91,7 +91,9 @@ export class SourceDocCodeLensProvider implements vscode.CodeLensProvider {
         }
 
         const lenses: vscode.CodeLens[] = [];
-        const firstRange = new vscode.Range(0, 0, 0, document.lineAt(0).text.length);
+        const firstRange = document.lineCount > 0
+            ? new vscode.Range(0, 0, 0, document.lineAt(0).text.length)
+            : new vscode.Range(0, 0, 0, 0);
 
         // File-level lens at line 0 — always shown (except 'none')
         lenses.push(
@@ -187,7 +189,7 @@ export class SourceDocCodeLensProvider implements vscode.CodeLensProvider {
         // For code languages: match function/class/method/def/fn declarations.
         const CODE_RE = /^[ \t]*((?:export\s+)?(?:default\s+)?(?:async\s+)?function[\s*]+\w+|(?:export\s+)?(?:abstract\s+|sealed\s+)?class\s+\w+|(?:export\s+)?(?:abstract\s+)?interface\s+\w+|(?:export\s+)?(?:const|let|var)\s+\w+\s*=\s*(?:async\s*)?(?:\([^)]*\)|\w+)\s*=>|(?:public|private|protected|internal)(?:\s+(?:static|override|virtual|abstract|async|readonly))*\s+\S+\s+\w+\s*[({]|def\s+\w+\s*\(|fn\s+\w+\s*[(<]|func\s+\w+\s*[(<])/;
 
-        const RE = isXml ? XAML_RE : CODE_RE;;
+        const RE = isXml ? XAML_RE : CODE_RE;
 
         // In block mode, pass the full element/function text as context.
         // For XAML, capture from the opening tag to the matching close or end-of-line.
diff --git a/src/explanationProvider.ts b/src/explanationProvider.ts
index c35bf85..8b8e142 100644
--- a/src/explanationProvider.ts
+++ b/src/explanationProvider.ts
@@ -76,12 +76,29 @@ export class ExplanationProvider implements vscode.Disposable {
             }
         } catch (err) {
             if (err instanceof vscode.LanguageModelError) {
-                throw new Error(`Copilot error (${err.code}): ${err.message}`);
+                switch (err.code) {
+                    case 'NoPermissions':
+                        throw new Error(`Copilot error (${err.code}): access denied. Please check your GitHub Copilot subscription.`);
+                    case 'Blocked':
+                        throw new Error(`Copilot error (${err.code}): request was blocked. Please check your GitHub Copilot settings.`);
+                    case 'NotFound':
+                        throw new Error(`Copilot error (${err.code}): model not found. Please check your GitHub Copilot extension.`);
+                    case 'RequestFailed':
+                        throw new Error(`Copilot error (${err.code}): request failed. Please try again.`);
+                    default:
+                        throw new Error(`Copilot error (${err.code}): ${err.message}. Please check your GitHub Copilot extension.`);
+                }
             }
             throw err;
         }
 
         result = result.trim();
+        if (token.isCancellationRequested) {
+            throw new vscode.CancellationError();
+        }
+        if (!result) {
+            throw new Error('Copilot returned an empty explanation. Please try again.');
+        }
         this.addToCache(key, result);
         return result;
     }
diff --git a/src/extension.ts b/src/extension.ts
index 4a69fbd..0b42d67 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -30,7 +30,13 @@ export function activate(context: vscode.ExtensionContext): void {
     );
 
     // ── Register CodeLens provider for each configured language ──────────────
-    registerCodeLensProviders(context, codeLensProvider);
+    // Track ALL registrations in languageRegistrations (not context.subscriptions)
+    // so the full set can be disposed when sourceDoc.languages changes.
+    let languageRegistrations: vscode.Disposable[] = [];
+    registerCodeLensProviders(codeLensProvider, languageRegistrations);
+
+    // Dispose the language registrations when the extension is deactivated.
+    context.subscriptions.push({ dispose: () => languageRegistrations.forEach(d => d.dispose()) });
 
     // Refresh lenses when the user switches to a different editor tab
     context.subscriptions.push(
@@ -43,13 +49,12 @@ export function activate(context: vscode.ExtensionContext): void {
     );
 
     // Re-register providers when sourceDoc.languages changes
-    let languageRegistrations: vscode.Disposable[] = [];
     context.subscriptions.push(
         vscode.workspace.onDidChangeConfiguration(e => {
             if (e.affectsConfiguration('sourceDoc.languages')) {
                 languageRegistrations.forEach(d => d.dispose());
                 languageRegistrations = [];
-                registerCodeLensProviders(context, codeLensProvider, languageRegistrations);
+                registerCodeLensProviders(codeLensProvider, languageRegistrations);
             }
         }),
     );
@@ -153,6 +158,11 @@ export function activate(context: vscode.ExtensionContext): void {
                     }
                 }
 
+                if (lines.length === 0) {
+                    vscode.window.showInformationMessage('Source Doc: nothing to explain in this file.');
+                    return;
+                }
+
                 await vscode.window.withProgress(
                     {
                         location: vscode.ProgressLocation.Window,
@@ -200,9 +210,8 @@ export function deactivate(): void {
 // ── Helpers ───────────────────────────────────────────────────────────────────
 
 function registerCodeLensProviders(
-    context: vscode.ExtensionContext,
     provider: SourceDocCodeLensProvider,
-    into: vscode.Disposable[] = context.subscriptions as unknown as vscode.Disposable[],
+    into: vscode.Disposable[],
 ): void {
     const config = vscode.workspace.getConfiguration('sourceDoc');
     const languages = config.get<string[]>('languages') ?? [