fix(tui): only offer auth_mode prompt after successful credential storage

Introduce a `credentialStored` flag in all 4 credential paths (OpenAI
API key, OpenAI OAuth, Anthropic auth token, Anthropic API key). The
auth_mode prompt is now gated on `credentialStored`, so a failed store
call no longer falls through to prompt the user for an auth mode that
was never set.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/frontends/tui/minimal.ts

@@ -1178,12 +1178,14 @@ export class MinimalTui {
         console.log(`${colors.gray}Create a key at:${colors.reset} https://platform.openai.com/api-keys`);
         console.log('');
 
+        let credentialStored = false;
         try {
           this.rl.pause();
           const apiKey = await promptHidden('Enter OpenAI API key: ');
           storeOpenAIApiKey(apiKey);
           console.log('');
           console.log(`${colors.gray}OpenAI API key stored in ~/.config/flynn/auth.json${colors.reset}\n`);
+          credentialStored = true;
         } catch (error) {
           const message = error instanceof Error ? error.message : String(error);
           console.log(`${colors.gray}OpenAI API key storage failed:${colors.reset} ${message}\n`);
@@ -1192,7 +1194,7 @@ export class MinimalTui {
         }
 
         // Offer to set auth_mode if config is available
-        if (this.config.currentConfig && this.config.configPath) {
+        if (credentialStored && this.config.currentConfig && this.config.configPath) {
           const modeInput = (await this.prompt(
             `${colors.orange}Set active auth mode?${colors.reset} ${colors.gray}[api_key/oauth/auto/skip] (default: skip):${colors.reset} `,
           )).trim().toLowerCase();
@@ -1218,6 +1220,7 @@ export class MinimalTui {
 
       console.log(`${colors.gray}Starting OpenAI OAuth device flow...${colors.reset}`);
 
+      let credentialStored = false;
       try {
         await loginOpenAI((userCode, verificationUri) => {
           console.log('');
@@ -1228,13 +1231,14 @@ export class MinimalTui {
         });
 
         console.log(`${colors.gray}OpenAI authentication successful! Token stored.${colors.reset}\n`);
+        credentialStored = true;
       } catch (error) {
         const message = error instanceof Error ? error.message : String(error);
         console.log(`${colors.gray}OpenAI login failed:${colors.reset} ${message}\n`);
       }
 
       // Offer to set auth_mode if config is available
-      if (this.config.currentConfig && this.config.configPath) {
+      if (credentialStored && this.config.currentConfig && this.config.configPath) {
         const modeInput = (await this.prompt(
           `${colors.orange}Set active auth mode?${colors.reset} ${colors.gray}[api_key/oauth/auto/skip] (default: skip):${colors.reset} `,
         )).trim().toLowerCase();
@@ -1270,12 +1274,14 @@ export class MinimalTui {
         console.log(`${colors.gray}Anthropic supports token-style auth (provider-specific).${colors.reset}`);
         console.log('');
 
+        let credentialStored = false;
         try {
           this.rl.pause();
           const token = await promptHidden('Enter Anthropic auth token: ');
           storeAnthropicAuthToken(token);
           console.log('');
           console.log(`${colors.gray}Anthropic auth token stored in ~/.config/flynn/auth.json${colors.reset}\n`);
+          credentialStored = true;
         } catch (error) {
           const message = error instanceof Error ? error.message : String(error);
           console.log(`${colors.gray}Anthropic auth failed:${colors.reset} ${message}\n`);
@@ -1284,7 +1290,7 @@ export class MinimalTui {
         }
 
         // Offer to set auth_mode if config is available
-        if (this.config.currentConfig && this.config.configPath) {
+        if (credentialStored && this.config.currentConfig && this.config.configPath) {
           const modeInput = (await this.prompt(
             `${colors.orange}Set active auth mode?${colors.reset} ${colors.gray}[api_key/oauth/auto/skip] (default: skip):${colors.reset} `,
           )).trim().toLowerCase();
@@ -1311,12 +1317,14 @@ export class MinimalTui {
       console.log(`${colors.gray}Create a key at:${colors.reset} https://console.anthropic.com/settings/keys`);
       console.log('');
 
+      let credentialStored = false;
       try {
         this.rl.pause();
         const apiKey = await promptHidden('Enter Anthropic API key: ');
         storeAnthropicAuth(apiKey);
         console.log('');
         console.log(`${colors.gray}Anthropic API key stored in ~/.config/flynn/auth.json${colors.reset}\n`);
+        credentialStored = true;
       } catch (error) {
         const message = error instanceof Error ? error.message : String(error);
         console.log(`${colors.gray}Anthropic auth failed:${colors.reset} ${message}\n`);
@@ -1325,7 +1333,7 @@ export class MinimalTui {
       }
 
       // Offer to set auth_mode if config is available
-      if (this.config.currentConfig && this.config.configPath) {
+      if (credentialStored && this.config.currentConfig && this.config.configPath) {
         const modeInput = (await this.prompt(
           `${colors.orange}Set active auth mode?${colors.reset} ${colors.gray}[api_key/oauth/auto/skip] (default: skip):${colors.reset} `,
         )).trim().toLowerCase();