diff --git a/src/ccs.ts b/src/ccs.ts
index 6706c057..54076490 100644
--- a/src/ccs.ts
+++ b/src/ccs.ts
@@ -37,7 +37,7 @@ import { handleShellCompletionCommand } from './commands/shell-completion-comman
 import { handleUpdateCommand } from './commands/update-command';
 
 // Import extracted utility functions
-import { execClaude, escapeShellArg } from './utils/shell-executor';
+import { execClaude, escapeShellArg, stripClaudeCodeEnv } from './utils/shell-executor';
 import { wireChildProcessSignals } from './utils/signal-forwarder';
 
 // Import target adapter system
@@ -197,13 +197,13 @@ async function execClaudeWithProxy(
   const needsShell = isWindows && /\.(cmd|bat)$/i.test(claudeCli);
   const webSearchEnv = getWebSearchHookEnv();
   const imageAnalysisEnv = getImageAnalysisHookEnv(profileName);
-  const env = {
+  const env = stripClaudeCodeEnv({
     ...process.env,
     ...envVars,
     ...webSearchEnv,
     ...imageAnalysisEnv,
     CCS_PROFILE_TYPE: 'settings', // Signal to WebSearch hook this is a third-party provider
-  };
+  });
 
   let claude: ChildProcess;
   if (isPowerShellScript) {
diff --git a/src/delegation/headless-executor.ts b/src/delegation/headless-executor.ts
index 9e2ad2c3..a4695560 100644
--- a/src/delegation/headless-executor.ts
+++ b/src/delegation/headless-executor.ts
@@ -17,6 +17,7 @@ import { StreamBuffer, formatToolVerbose } from './executor/stream-parser';
 import { buildExecutionResult } from './executor/result-aggregator';
 import { getCcsDir, getModelDisplayName } from '../utils/config-manager';
 import { getProfileLookupCandidates } from '../utils/profile-compat';
+import { stripClaudeCodeEnv } from '../utils/shell-executor';
 
 // Re-export types for consumers
 export type { ExecutionOptions, ExecutionResult, StreamMessage } from './executor/types';
@@ -209,7 +210,7 @@ export class HeadlessExecutor {
 
       // Strip Claude Code nested session guard env var to allow CCS delegation
       // (Claude Code v2.1.39+ sets CLAUDECODE to detect nested sessions)
-      const { CLAUDECODE: _nested, ...cleanEnv } = process.env;
+      const cleanEnv = stripClaudeCodeEnv(process.env);
 
       const proc = spawn(claudeCli, args, {
         cwd,
diff --git a/src/utils/shell-executor.ts b/src/utils/shell-executor.ts
index e8a8b93f..d8ea89d3 100644
--- a/src/utils/shell-executor.ts
+++ b/src/utils/shell-executor.ts
@@ -24,6 +24,22 @@ export function stripAnthropicEnv(env: NodeJS.ProcessEnv): NodeJS.ProcessEnv {
   return result;
 }
 
+/**
+ * Strip Claude Code nested-session guard env var from a process environment.
+ *
+ * Note: Windows env keys are case-insensitive, so remove case-insensitively
+ * to avoid missing variants like `claudecode`.
+ */
+export function stripClaudeCodeEnv(env: NodeJS.ProcessEnv): NodeJS.ProcessEnv {
+  const result: NodeJS.ProcessEnv = {};
+  for (const key of Object.keys(env)) {
+    if (key.toUpperCase() !== 'CLAUDECODE') {
+      result[key] = env[key];
+    }
+  }
+  return result;
+}
+
 /**
  * Escape arguments for shell execution (cross-platform)
  *
@@ -80,13 +96,13 @@ export function execClaude(
       : process.env;
 
   // Prepare environment (merge with base env if envVars provided)
-  const env = envVars
+  const mergedEnv = envVars
     ? { ...baseEnv, ...envVars, ...webSearchEnv }
     : { ...baseEnv, ...webSearchEnv };
 
   // Strip Claude Code nested session guard env var to allow CCS delegation
   // (Claude Code v2.1.39+ sets CLAUDECODE to detect nested sessions)
-  delete env.CLAUDECODE;
+  const env = stripClaudeCodeEnv(mergedEnv);
 
   // propagate key env vars to tmux session so agent team teammates
   // (spawned via tmux split-window) inherit the correct config dir