diff --git a/src/auth/auth-commands.ts b/src/auth/auth-commands.ts
index dcd248b3..7556094e 100644
--- a/src/auth/auth-commands.ts
+++ b/src/auth/auth-commands.ts
@@ -242,8 +242,8 @@ class AuthCommands {
   /**
    * Reset default profile - delegates to default-command.ts
    */
-  async handleResetDefault(): Promise<void> {
-    return handleResetDefault(this.getContext());
+  async handleResetDefault(args: string[] = []): Promise<void> {
+    return handleResetDefault(this.getContext(), args);
   }
 
   /**
@@ -297,7 +297,7 @@ class AuthCommands {
         break;
 
       case 'reset-default':
-        await this.handleResetDefault();
+        await this.handleResetDefault(commandArgs);
         break;
 
       case 'current':
diff --git a/src/auth/commands/backup-command.ts b/src/auth/commands/backup-command.ts
index e66068be..f6fe167d 100644
--- a/src/auth/commands/backup-command.ts
+++ b/src/auth/commands/backup-command.ts
@@ -11,7 +11,7 @@ import {
 } from '../resume-lane-diagnostics';
 import { isAccountContextMetadata, resolveAccountContextPolicy } from '../account-context';
 import { isProfileLocalSharedResourceMode } from '../shared-resource-policy';
-import { CommandContext, parseArgs } from './types';
+import { CommandContext, parseArgs, rejectUnsupportedAuthOptions } from './types';
 
 interface BackupManifest {
   target: string;
@@ -37,7 +37,11 @@ function copyDirectoryIfPresent(sourcePath: string, targetPath: string): boolean
 
 export async function handleBackup(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { profileName, json } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { profileName, json } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth backup <profile|default> [--json]',
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
diff --git a/src/auth/commands/create-command.ts b/src/auth/commands/create-command.ts
index d407ace4..b0cd4aad 100644
--- a/src/auth/commands/create-command.ts
+++ b/src/auth/commands/create-command.ts
@@ -27,7 +27,7 @@ import {
 } from '../shared-resource-policy';
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, parseArgs } from './types';
+import { CommandContext, parseArgs, rejectUnsupportedAuthOptions } from './types';
 import { stripAmbientProviderCredentials } from './create-command-env';
 import { isUnifiedMode } from '../../config/config-loader-facade';
 
@@ -40,29 +40,13 @@ function sanitizeProfileNameForInstance(name: string): string {
  */
 export async function handleCreate(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const {
-    profileName,
-    force,
-    shareContext,
-    contextGroup,
-    deeperContinuity,
-    bare,
-    mode,
-    unknownFlags,
-  } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { profileName, force, shareContext, contextGroup, deeperContinuity, bare } = parsed;
 
-  const unsupportedOptions = [...(unknownFlags ?? []), ...(mode !== undefined ? ['--mode'] : [])];
-  if (unsupportedOptions.length > 0) {
-    const unknownList = unsupportedOptions.map((flag) => `"${flag}"`).join(', ');
-    console.log(fail(`Unknown option(s): ${unknownList}`));
-    console.log('');
-    console.log(
-      `Usage: ${color('ccs auth create <profile> [--force] [--bare] [--share-context] [--context-group <name>] [--deeper-continuity]', 'command')}`
-    );
-    console.log(`Help:  ${color('ccs auth --help', 'command')}`);
-    console.log('');
-    exitWithError(`Unknown option(s): ${unknownList}`, ExitCode.PROFILE_ERROR);
-  }
+  rejectUnsupportedAuthOptions(parsed, {
+    usage:
+      'ccs auth create <profile> [--force] [--bare] [--share-context] [--context-group <name>] [--deeper-continuity]',
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
diff --git a/src/auth/commands/default-command.ts b/src/auth/commands/default-command.ts
index 2800f931..8836aee1 100644
--- a/src/auth/commands/default-command.ts
+++ b/src/auth/commands/default-command.ts
@@ -8,7 +8,7 @@ import { initUI, color, dim, ok, fail } from '../../utils/ui';
 
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, parseArgs } from './types';
+import { CommandContext, parseArgs, rejectUnsupportedAuthOptions } from './types';
 import { isUnifiedMode } from '../../config/config-loader-facade';
 
 /**
@@ -16,7 +16,11 @@ import { isUnifiedMode } from '../../config/config-loader-facade';
  */
 export async function handleDefault(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { profileName } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { profileName } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth default <profile>',
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
@@ -48,8 +52,12 @@ export async function handleDefault(ctx: CommandContext, args: string[]): Promis
 /**
  * Handle the reset-default command (clear the custom default)
  */
-export async function handleResetDefault(ctx: CommandContext): Promise<void> {
+export async function handleResetDefault(ctx: CommandContext, args: string[] = []): Promise<void> {
   await initUI();
+  const parsed = parseArgs(args);
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth reset-default',
+  });
 
   try {
     // Use unified or legacy based on config mode
diff --git a/src/auth/commands/list-command.ts b/src/auth/commands/list-command.ts
index 9172e90b..88646d0d 100644
--- a/src/auth/commands/list-command.ts
+++ b/src/auth/commands/list-command.ts
@@ -10,14 +10,24 @@ import { resolveAccountContextPolicy, formatAccountContextPolicy } from '../acco
 import { resolveSharedResourcePolicy } from '../shared-resource-policy';
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, ListOutput, parseArgs, formatRelativeTime } from './types';
+import {
+  CommandContext,
+  ListOutput,
+  parseArgs,
+  formatRelativeTime,
+  rejectUnsupportedAuthOptions,
+} from './types';
 
 /**
  * Handle the list command
  */
 export async function handleList(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { verbose, json } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { verbose, json } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth list [--verbose] [--json]',
+  });
 
   try {
     // Get profiles from both legacy (profiles.json) and unified config (config.yaml)
diff --git a/src/auth/commands/remove-command.ts b/src/auth/commands/remove-command.ts
index 9302d1b0..fed45098 100644
--- a/src/auth/commands/remove-command.ts
+++ b/src/auth/commands/remove-command.ts
@@ -11,7 +11,7 @@ import { InteractivePrompt } from '../../utils/prompt';
 
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, parseArgs } from './types';
+import { CommandContext, parseArgs, rejectUnsupportedAuthOptions } from './types';
 import { isUnifiedMode } from '../../config/config-loader-facade';
 
 /**
@@ -19,7 +19,11 @@ import { isUnifiedMode } from '../../config/config-loader-facade';
  */
 export async function handleRemove(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { profileName, yes } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { profileName, yes } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth remove <profile> [--yes]',
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
diff --git a/src/auth/commands/resources-command.ts b/src/auth/commands/resources-command.ts
index a20998b8..f3269457 100644
--- a/src/auth/commands/resources-command.ts
+++ b/src/auth/commands/resources-command.ts
@@ -8,7 +8,7 @@ import {
 } from '../shared-resource-policy';
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, parseArgs } from './types';
+import { CommandContext, parseArgs, rejectUnsupportedAuthOptions } from './types';
 
 function formatMode(mode: SharedResourceMode): string {
   return mode === 'profile-local' ? 'profile-local' : 'shared';
@@ -22,7 +22,12 @@ function modeDescription(mode: SharedResourceMode): string {
 
 export async function handleResources(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { profileName, mode, json } = parseArgs(args);
+  const parsed = parseArgs(args, { allowMode: true });
+  const { profileName, mode, json } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth resources <profile> [--mode shared|profile-local] [--json]',
+    allowMode: true,
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
diff --git a/src/auth/commands/show-command.ts b/src/auth/commands/show-command.ts
index 212ef7a1..37602688 100644
--- a/src/auth/commands/show-command.ts
+++ b/src/auth/commands/show-command.ts
@@ -13,7 +13,7 @@ import { resolveConfiguredPlainCcsResumeLane } from '../resume-lane-diagnostics'
 import { resolveSharedResourcePolicy } from '../shared-resource-policy';
 import { exitWithError } from '../../errors';
 import { ExitCode } from '../../errors/exit-codes';
-import { CommandContext, ProfileOutput, parseArgs } from './types';
+import { CommandContext, ProfileOutput, parseArgs, rejectUnsupportedAuthOptions } from './types';
 
 function formatHistorySummary(history: ReturnType<typeof summarizeAccountHistory>): string {
   const scope = history.projects_shared ? 'shared projects' : 'profile-local projects';
@@ -26,7 +26,11 @@ function formatHistorySummary(history: ReturnType<typeof summarizeAccountHistory
  */
 export async function handleShow(ctx: CommandContext, args: string[]): Promise<void> {
   await initUI();
-  const { profileName, json } = parseArgs(args);
+  const parsed = parseArgs(args);
+  const { profileName, json } = parsed;
+  rejectUnsupportedAuthOptions(parsed, {
+    usage: 'ccs auth show <profile> [--json]',
+  });
 
   if (!profileName) {
     console.log(fail('Profile name is required'));
diff --git a/src/auth/commands/types.ts b/src/auth/commands/types.ts
index 906f7135..f091b410 100644
--- a/src/auth/commands/types.ts
+++ b/src/auth/commands/types.ts
@@ -6,6 +6,9 @@
 
 import ProfileRegistry from '../profile-registry';
 import { InstanceManager } from '../../management/instance-manager';
+import { exitWithError } from '../../errors';
+import { ExitCode } from '../../errors/exit-codes';
+import { color, fail } from '../../utils/ui';
 
 // Re-export for backward compatibility
 export { formatRelativeTime } from '../../utils/time';
@@ -83,10 +86,36 @@ export interface CommandContext {
   version: string;
 }
 
+export function rejectUnsupportedAuthOptions(
+  parsed: Pick<AuthCommandArgs, 'mode' | 'unknownFlags'>,
+  options: { usage: string; allowMode?: boolean }
+): void {
+  const unsupportedOptions = [
+    ...(parsed.unknownFlags ?? []),
+    ...(!options.allowMode && parsed.mode !== undefined ? ['--mode'] : []),
+  ];
+
+  if (unsupportedOptions.length === 0) {
+    return;
+  }
+
+  const unknownList = unsupportedOptions.map((flag) => `"${flag}"`).join(', ');
+  console.log(fail(`Unknown option(s): ${unknownList}`));
+  console.log('');
+  console.log(`Usage: ${color(options.usage, 'command')}`);
+  console.log(`Help:  ${color('ccs auth --help', 'command')}`);
+  console.log('');
+  exitWithError(`Unknown option(s): ${unknownList}`, ExitCode.PROFILE_ERROR);
+}
+
+interface ParseArgsOptions {
+  allowMode?: boolean;
+}
+
 /**
  * Parse command arguments from raw args array
  */
-export function parseArgs(args: string[]): AuthCommandArgs {
+export function parseArgs(args: string[], options: ParseArgsOptions = {}): AuthCommandArgs {
   let profileName: string | undefined;
   let contextGroup: string | undefined;
   let mode: string | undefined;
@@ -101,7 +130,10 @@ export function parseArgs(args: string[]): AuthCommandArgs {
     '--deeper-continuity',
     '--bare',
   ]);
-  const knownValueFlags = new Set(['--context-group', '--mode']);
+  const knownValueFlags = new Set(['--context-group']);
+  if (options.allowMode) {
+    knownValueFlags.add('--mode');
+  }
 
   for (let i = 0; i < args.length; i++) {
     const arg = args[i];
@@ -118,7 +150,7 @@ export function parseArgs(args: string[]): AuthCommandArgs {
       continue;
     }
 
-    if (arg === '--mode') {
+    if (options.allowMode && arg === '--mode') {
       const next = args[i + 1];
       if (!next || next.startsWith('-')) {
         mode = '';
@@ -135,7 +167,7 @@ export function parseArgs(args: string[]): AuthCommandArgs {
       continue;
     }
 
-    if (arg.startsWith('--mode=')) {
+    if (options.allowMode && arg.startsWith('--mode=')) {
       mode = arg.slice('--mode='.length);
       continue;
     }
diff --git a/tests/unit/auth-command-args.test.ts b/tests/unit/auth-command-args.test.ts
index 7673dee4..9badc1f2 100644
--- a/tests/unit/auth-command-args.test.ts
+++ b/tests/unit/auth-command-args.test.ts
@@ -64,19 +64,27 @@ describe('auth command args parsing', () => {
   });
 
   it('parses shared resource mode value for resources command', () => {
-    const parsed = parseArgs(['work', '--mode', 'profile-local']);
+    const parsed = parseArgs(['work', '--mode', 'profile-local'], { allowMode: true });
 
     expect(parsed.profileName).toBe('work');
     expect(parsed.mode).toBe('profile-local');
   });
 
   it('parses inline shared resource mode value', () => {
-    const parsed = parseArgs(['work', '--mode=shared']);
+    const parsed = parseArgs(['work', '--mode=shared'], { allowMode: true });
 
     expect(parsed.profileName).toBe('work');
     expect(parsed.mode).toBe('shared');
   });
 
+  it('treats shared resource mode as unknown unless the command opts in', () => {
+    const parsed = parseArgs(['work', '--mode', 'shared']);
+
+    expect(parsed.profileName).toBe('work');
+    expect(parsed.mode).toBeUndefined();
+    expect(parsed.unknownFlags).toEqual(['--mode']);
+  });
+
   it('tracks unknown flags and keeps positional profile intact', () => {
     const parsed = parseArgs(['--foo', 'bar', 'work']);
 
diff --git a/tests/unit/auth-resources-command.test.ts b/tests/unit/auth-resources-command.test.ts
index d76bc36f..88379cfe 100644
--- a/tests/unit/auth-resources-command.test.ts
+++ b/tests/unit/auth-resources-command.test.ts
@@ -6,6 +6,38 @@ import ProfileRegistry from '../../src/auth/profile-registry';
 import InstanceManager from '../../src/management/instance-manager';
 import { handleResources } from '../../src/auth/commands/resources-command';
 import { handleCreate } from '../../src/auth/commands/create-command';
+import { handleList } from '../../src/auth/commands/list-command';
+import { handleShow } from '../../src/auth/commands/show-command';
+import { handleBackup } from '../../src/auth/commands/backup-command';
+import { handleRemove } from '../../src/auth/commands/remove-command';
+import { handleDefault, handleResetDefault } from '../../src/auth/commands/default-command';
+
+async function expectProfileExit(action: () => Promise<void>): Promise<string> {
+  const originalExit = process.exit;
+  const originalLog = console.log;
+  const originalError = console.error;
+  const lines: string[] = [];
+
+  process.exit = ((code?: number) => {
+    throw new Error(`process.exit(${code ?? 0})`);
+  }) as typeof process.exit;
+  console.log = (...args: unknown[]) => {
+    lines.push(args.map(String).join(' '));
+  };
+  console.error = (...args: unknown[]) => {
+    lines.push(args.map(String).join(' '));
+  };
+
+  try {
+    await expect(action()).rejects.toThrow('process.exit(7)');
+  } finally {
+    process.exit = originalExit;
+    console.log = originalLog;
+    console.error = originalError;
+  }
+
+  return lines.join('\n');
+}
 
 describe('auth resources command', () => {
   let tempRoot = '';
@@ -143,38 +175,37 @@ describe('auth resources command', () => {
   it('rejects --mode on auth create instead of silently ignoring it', async () => {
     const registry = new ProfileRegistry();
     const instanceMgr = new InstanceManager();
-    const originalExit = process.exit;
-    const originalLog = console.log;
-    const originalError = console.error;
-    const lines: string[] = [];
 
-    process.exit = ((code?: number) => {
-      throw new Error(`process.exit(${code ?? 0})`);
-    }) as typeof process.exit;
-    console.log = (...args: unknown[]) => {
-      lines.push(args.map(String).join(' '));
-    };
-    console.error = (...args: unknown[]) => {
-      lines.push(args.map(String).join(' '));
-    };
+    const output = await expectProfileExit(() =>
+      handleCreate(
+        {
+          registry,
+          instanceMgr,
+          version: 'test',
+        },
+        ['work', '--mode', 'profile-local']
+      )
+    );
 
-    try {
-      await expect(
-        handleCreate(
-          {
-            registry,
-            instanceMgr,
-            version: 'test',
-          },
-          ['work', '--mode', 'profile-local']
-        )
-      ).rejects.toThrow('process.exit(7)');
-    } finally {
-      process.exit = originalExit;
-      console.log = originalLog;
-      console.error = originalError;
+    expect(output).toContain('Unknown option(s): "--mode"');
+  });
+
+  it('rejects --mode on non-resources auth commands instead of silently ignoring it', async () => {
+    const registry = new ProfileRegistry();
+    const instanceMgr = new InstanceManager();
+    const ctx = { registry, instanceMgr, version: 'test' };
+    const cases: Array<[string, () => Promise<void>]> = [
+      ['list', () => handleList(ctx, ['--mode', 'shared'])],
+      ['show', () => handleShow(ctx, ['work', '--mode=shared'])],
+      ['backup', () => handleBackup(ctx, ['work', '--mode', 'profile-local'])],
+      ['remove', () => handleRemove(ctx, ['work', '--mode', 'shared'])],
+      ['default', () => handleDefault(ctx, ['work', '--mode', 'shared'])],
+      ['reset-default', () => handleResetDefault(ctx, ['--mode', 'shared'])],
+    ];
+
+    for (const [commandName, action] of cases) {
+      const output = await expectProfileExit(action);
+      expect(`${commandName}\n${output}`).toContain('Unknown option(s): "--mode"');
     }
-
-    expect(lines.join('\n')).toContain('Unknown option(s): "--mode"');
   });
 });