fix(gemini): wire --resume flag through to Gemini backend

cli/src/commands/gemini.ts

@@ -15,6 +15,7 @@ export const geminiCommand: CommandDefinition = {
                 startingMode?: 'local' | 'remote'
                 permissionMode?: GeminiPermissionMode
                 model?: string
+                resumeSessionId?: string
             } = {}
 
             for (let i = 0; i < commandArgs.length; i++) {
@@ -30,6 +31,12 @@ export const geminiCommand: CommandDefinition = {
                     }
                 } else if (arg === '--yolo') {
                     options.permissionMode = 'yolo'
+                } else if (arg === '--resume') {
+                    const sessionId = commandArgs[++i]
+                    if (!sessionId) {
+                        throw new Error('Missing --resume value')
+                    }
+                    options.resumeSessionId = sessionId
                 } else if (arg === '--model') {
                     const model = commandArgs[++i]
                     if (!model) {

cli/src/gemini/geminiRemoteLauncher.ts

@@ -54,7 +54,6 @@ class GeminiRemoteLauncher extends RemoteLauncherBase {
         const backend = createGeminiBackend({
             model: runtimeConfig.model,
             token: runtimeConfig.token,
-            resumeSessionId: session.sessionId,
             hookSettingsPath: this.hookSettingsPath,
             cwd: session.path,
             permissionMode: session.getPermissionMode() as string | undefined
@@ -69,10 +68,33 @@ class GeminiRemoteLauncher extends RemoteLauncherBase {
 
         await backend.initialize();
 
-        const acpSessionId = await backend.newSession({
-            cwd: session.path,
-            mcpServers: toAcpMcpServers(mcpServers)
-        });
+        const resumeSessionId = session.sessionId;
+        const acpMcpServers = toAcpMcpServers(mcpServers);
+        let acpSessionId: string;
+        if (resumeSessionId) {
+            try {
+                acpSessionId = await backend.loadSession({
+                    sessionId: resumeSessionId,
+                    cwd: session.path,
+                    mcpServers: acpMcpServers
+                });
+            } catch (error) {
+                logger.warn('[gemini-remote] resume failed, starting new session', error);
+                session.sendSessionEvent({
+                    type: 'message',
+                    message: 'Gemini resume failed; starting a new session.'
+                });
+                acpSessionId = await backend.newSession({
+                    cwd: session.path,
+                    mcpServers: acpMcpServers
+                });
+            }
+        } else {
+            acpSessionId = await backend.newSession({
+                cwd: session.path,
+                mcpServers: acpMcpServers
+            });
+        }
         session.onSessionFound(acpSessionId);
 
         this.permissionHandler = new GeminiPermissionHandler(
@@ -115,12 +137,13 @@ class GeminiRemoteLauncher extends RemoteLauncherBase {
                     this.handleAgentMessage(message);
                 });
             } catch (error) {
-                logger.warn('[gemini-remote] prompt failed', error);
+                const errorMessage = error instanceof Error ? error.message : String(error);
+                logger.warn('[gemini-remote] prompt failed', { message: errorMessage });
                 session.sendSessionEvent({
                     type: 'message',
-                    message: 'Gemini prompt failed. Check logs for details.'
+                    message: `Gemini prompt failed: ${errorMessage}`
                 });
-                messageBuffer.addMessage('Gemini prompt failed', 'status');
+                messageBuffer.addMessage(`Gemini prompt failed: ${errorMessage}`, 'status');
             } finally {
                 session.onThinkingChange(false);
                 await this.permissionHandler?.cancelAll('Prompt finished');

cli/src/gemini/loop.ts

@@ -19,6 +19,7 @@ interface GeminiLoopOptions {
     model?: string;
     hookSettingsPath?: string;
     allowedTools?: string[];
+    resumeSessionId?: string;
     onSessionReady?: (session: GeminiSession) => void;
 }
 
@@ -31,7 +32,7 @@ export async function geminiLoop(opts: GeminiLoopOptions): Promise<void> {
         api: opts.api,
         client: opts.session,
         path: opts.path,
-        sessionId: null,
+        sessionId: opts.resumeSessionId ?? null,
         logPath,
         messageQueue: opts.messageQueue,
         onModeChange: opts.onModeChange,
@@ -41,6 +42,10 @@ export async function geminiLoop(opts: GeminiLoopOptions): Promise<void> {
         permissionMode: opts.permissionMode ?? 'default'
     });
 
+    if (opts.resumeSessionId) {
+        session.onSessionFound(opts.resumeSessionId);
+    }
+
     await runLocalRemoteSession({
         session,
         startingMode: opts.startingMode,

cli/src/gemini/runGemini.test.ts

@@ -106,4 +106,26 @@ describe('runGemini', () => {
         expect(harness.bootstrapArgs[0]?.model).toBeUndefined();
         expect(harness.geminiLoopArgs[0]?.model).toBe('gemini-2.5-pro');
     });
+
+    it('passes resumeSessionId through to geminiLoop', async () => {
+        resolveGeminiRuntimeConfigMock.mockReturnValue({
+            model: 'gemini-2.5-pro',
+            modelSource: 'default'
+        });
+
+        await runGemini({ resumeSessionId: 'a6157ffa-f692-4b73-82d5-63d42177f4f9' });
+
+        expect(harness.geminiLoopArgs[0]?.resumeSessionId).toBe('a6157ffa-f692-4b73-82d5-63d42177f4f9');
+    });
+
+    it('does not set resumeSessionId when not provided', async () => {
+        resolveGeminiRuntimeConfigMock.mockReturnValue({
+            model: 'gemini-2.5-pro',
+            modelSource: 'default'
+        });
+
+        await runGemini({});
+
+        expect(harness.geminiLoopArgs[0]?.resumeSessionId).toBeUndefined();
+    });
 });

cli/src/gemini/runGemini.ts

@@ -21,6 +21,7 @@ export async function runGemini(opts: {
     startingMode?: 'local' | 'remote';
     permissionMode?: PermissionMode;
     model?: string;
+    resumeSessionId?: string;
 } = {}): Promise<void> {
     const workingDirectory = getInvokedCwd();
     const startedBy = opts.startedBy ?? 'terminal';
@@ -149,6 +150,7 @@ export async function runGemini(opts: {
             permissionMode: currentPermissionMode,
             model: resolvedModel,
             hookSettingsPath,
+            resumeSessionId: opts.resumeSessionId,
             onModeChange: createModeChangeHandler(session),
             onSessionReady: (instance) => {
                 sessionWrapperRef.current = instance;