Support completion of checkpoint names in /resume (#1063)

packages/cli/src/ui/components/InputPrompt.tsx

@@ -109,11 +109,20 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
       const selectedSuggestion = completionSuggestions[indexToUse];
 
       if (query.trimStart().startsWith('/')) {
+        const parts = query.trimStart().substring(1).split(' ');
+        const commandName = parts[0];
         const slashIndex = query.indexOf('/');
         const base = query.substring(0, slashIndex + 1);
-        const newValue = base + selectedSuggestion.value;
-        buffer.setText(newValue);
-        handleSubmitAndClear(newValue);
+
+        const command = slashCommands.find((cmd) => cmd.name === commandName);
+        if (command && command.completion) {
+          const newValue = `${base}${commandName} ${selectedSuggestion.value}`;
+          buffer.setText(newValue);
+        } else {
+          const newValue = base + selectedSuggestion.value;
+          buffer.setText(newValue);
+          handleSubmitAndClear(newValue);
+        }
       } else {
         const atIndex = query.lastIndexOf('@');
         if (atIndex === -1) return;
@@ -131,7 +140,13 @@ export const InputPrompt: React.FC<InputPromptProps> = ({
       }
       resetCompletionState();
     },
-    [resetCompletionState, handleSubmitAndClear, buffer, completionSuggestions],
+    [
+      resetCompletionState,
+      handleSubmitAndClear,
+      buffer,
+      completionSuggestions,
+      slashCommands,
+    ],
   );
 
   useInput(

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -44,6 +44,7 @@ export interface SlashCommand {
   name: string;
   altName?: string;
   description?: string;
+  completion?: () => Promise<string[]>;
   action: (
     mainCommand: string,
     subCommand?: string,
@@ -643,6 +644,25 @@ Add any other context about the problem here.
         name: 'resume',
         description:
           'resume from conversation checkpoint. Usage: /resume [tag]',
+        completion: async () => {
+          const geminiDir = config?.getGeminiDir();
+          if (!geminiDir) {
+            return [];
+          }
+          try {
+            const files = await fs.readdir(geminiDir);
+            return files
+              .filter(
+                (file) =>
+                  file.startsWith('checkpoint-') && file.endsWith('.json'),
+              )
+              .map((file) =>
+                file.replace('checkpoint-', '').replace('.json', ''),
+              );
+          } catch (_err) {
+            return [];
+          }
+        },
         action: async (_mainCommand, subCommand, _args) => {
           const tag = (subCommand || '').trim();
           const logger = new Logger(config?.getSessionId() || '');

packages/cli/src/ui/hooks/useCompletion.ts

@@ -127,6 +127,34 @@ export function useCompletion(
 
     // --- Handle Slash Command Completion ---
     if (trimmedQuery.startsWith('/')) {
+      const parts = trimmedQuery.substring(1).split(' ');
+      const commandName = parts[0];
+      const subCommand = parts.slice(1).join(' ');
+
+      const command = slashCommands.find(
+        (cmd) => cmd.name === commandName || cmd.altName === commandName,
+      );
+
+      if (command && command.completion) {
+        const fetchAndSetSuggestions = async () => {
+          setIsLoadingSuggestions(true);
+          if (command.completion) {
+            const results = await command.completion();
+            const filtered = results.filter((r) => r.startsWith(subCommand));
+            const newSuggestions = filtered.map((s) => ({
+              label: s,
+              value: s,
+            }));
+            setSuggestions(newSuggestions);
+            setShowSuggestions(newSuggestions.length > 0);
+            setActiveSuggestionIndex(newSuggestions.length > 0 ? 0 : -1);
+          }
+          setIsLoadingSuggestions(false);
+        };
+        fetchAndSetSuggestions();
+        return;
+      }
+
       const partialCommand = trimmedQuery.substring(1);
       const filteredSuggestions = slashCommands
         .filter(