diff --git a/src/cli/index.ts b/src/cli/index.ts
index 98a8fd8..457282d 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -31,7 +31,7 @@ import type {
   CodexPromptEnvelope,
   ContextLogEntry
 } from '../types/codex-context.js';
-import { RetryManager } from '../core/errors.js';
+import { RetryManager, DaemonConflictError } from '../core/errors.js';
 import { HiveMindYamlFormatter } from '../utils/yaml-output.js';
 import { parseFileContent, parseJsonInput, loadFileThroughFeedforward } from './feedforward.js';
 import { InstructionParser } from '../instructions/index.js';
@@ -599,10 +599,15 @@ async function useSystem(description: string, fn: (system: CodexSynapticSystem)
   if (!alreadyRunning && process.env.CODEX_ALLOW_LOCAL_WITH_DAEMON !== '1') {
     const background = getBackgroundStatus();
     if (background.running) {
-      throw new Error(
+      throw new DaemonConflictError(
         `Background daemon already running (pid ${background.pid}). ` +
         'To avoid split-brain state, use `codex-synaptic background attach` for daemon-backed monitoring, ' +
-        '`codex-synaptic background stop` before local commands, or set CODEX_ALLOW_LOCAL_WITH_DAEMON=1 to override.'
+        '`codex-synaptic background stop` before local commands, or set CODEX_ALLOW_LOCAL_WITH_DAEMON=1 to override.',
+        {
+          daemonPid: background.pid,
+          alreadyRunning,
+          allowLocalWithDaemon: process.env.CODEX_ALLOW_LOCAL_WITH_DAEMON
+        }
       );
     }
   }
diff --git a/src/core/errors.ts b/src/core/errors.ts
index 00700ad..2585f2e 100644
--- a/src/core/errors.ts
+++ b/src/core/errors.ts
@@ -35,7 +35,10 @@ export enum ErrorCode {
   // Bridge errors
   BRIDGE_ERROR = 'BRIDGE_ERROR',
   MCP_ERROR = 'MCP_ERROR',
-  A2A_ERROR = 'A2A_ERROR'
+  A2A_ERROR = 'A2A_ERROR',
+  
+  // CLI/Daemon errors
+  DAEMON_CONFLICT = 'DAEMON_CONFLICT'
 }
 
 export class CodexSynapticError extends Error {
@@ -111,6 +114,16 @@ export class BridgeError extends CodexSynapticError {
   }
 }
 
+/**
+ * Error thrown when a daemon conflict is detected (split-brain prevention)
+ */
+export class DaemonConflictError extends CodexSynapticError {
+  constructor(message: string, context?: Record<string, any>) {
+    super(ErrorCode.DAEMON_CONFLICT, message, context, false);
+    this.name = 'DaemonConflictError';
+  }
+}
+
 /**
  * Circuit breaker for handling failures gracefully
  */