refactor(cli): simplify agent mode validation flow

What I changed:
- extracted a single missingModeError helper in agent/mode.ts so the command no longer duplicates the same command error payload in two branches
- flattened control flow by returning early for --list and using one set-mode path guarded by explicit missing-mode validation
- tightened tests/10-agent-mode.test.ts to assert the exact missing-mode error message instead of allowing a daemon-connection fallback

Reasoning:
- this keeps behavior the same while reducing branch duplication and making the validation contract explicit
- the hardened test protects the intended precedence: missing required mode should fail before any daemon interaction

Verification:
- npm run typecheck
- (cd packages/cli && npx tsx tests/10-agent-mode.test.ts)

Notes for next agent:
- repository had a pre-existing local modification in scripts/codex-refactor-loop.sh; I intentionally did not touch or stage it
- no blockers encountered for this refactor

packages/cli/src/commands/agent/mode.ts

@@ -37,6 +37,12 @@ export interface AgentModeOptions extends CommandOptions {
   list?: boolean
 }
 
+const missingModeError = (): CommandError => ({
+  code: 'MISSING_ARGUMENT',
+  message: 'Mode argument required unless --list is specified',
+  details: 'Usage: paseo agent mode <id> <mode> | paseo agent mode --list <id>',
+})
+
 // This command returns two different data shapes (set result vs mode list).
 // Keep `any` here to match the existing output wrapper generic contract.
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
@@ -53,12 +59,7 @@ export async function runModeCommand(
 
   // Validate arguments
   if (!options.list && !normalizedMode) {
-    const error: CommandError = {
+    throw missingModeError()
-      code: 'MISSING_ARGUMENT',
-      message: 'Mode argument required unless --list is specified',
-      details: 'Usage: paseo agent mode <id> <mode> | paseo agent mode --list <id>',
-    }
-    throw error
   }
 
   let client: Awaited<ReturnType<typeof connectToDaemon>> | undefined
@@ -90,14 +91,10 @@ export async function runModeCommand(
         data: items,
         schema: modeListSchema,
       }
-    } else {
-      if (!normalizedMode) {
-        const error: CommandError = {
-          code: 'MISSING_ARGUMENT',
-          message: 'Mode argument required unless --list is specified',
-          details: 'Usage: paseo agent mode <id> <mode> | paseo agent mode --list <id>',
     }
-        throw error
+
+    if (!normalizedMode) {
+      throw missingModeError()
     }
 
     // Set the agent mode
@@ -111,7 +108,6 @@ export async function runModeCommand(
       },
       schema: setModeSchema,
     }
-    }
   } catch (err) {
     // Re-throw if it's already a CommandError
     if (err && typeof err === 'object' && 'code' in err) {

packages/cli/tests/10-agent-mode.test.ts

@@ -125,12 +125,10 @@ try {
     // Should fail because mode is required unless --list is specified
     assert.notStrictEqual(result.exitCode, 0, 'should fail without mode argument')
     const output = result.stdout + result.stderr
-    const hasError =
+    assert(
-      output.toLowerCase().includes('missing') ||
+      output.includes('Mode argument required unless --list is specified'),
-      output.toLowerCase().includes('required') ||
+      'error should mention missing mode argument'
-      output.toLowerCase().includes('mode') ||
+    )
-      output.toLowerCase().includes('daemon') // If daemon error comes first, that's also valid
-    assert(hasError, 'error should mention missing mode or connection issue')
     console.log('✓ agent mode requires mode argument when not using --list\n')
   }
 } finally {