fix(delegation): strip CLAUDECODE env var to bypass nested session guard

Claude Code v2.1.39+ sets CLAUDECODE env var and refuses to launch
if detected, breaking CCS auto-delegation which spawns child Claude
processes. Strip the var from both interactive (execClaude) and
headless (HeadlessExecutor) spawn paths.

Closes #588

src/delegation/headless-executor.ts

@@ -207,10 +207,15 @@ export class HeadlessExecutor {
         console.error(ui.info(`Delegating to ${modelName}...`));
       }
 
+      // 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 proc = spawn(claudeCli, args, {
         cwd,
         stdio: ['ignore', 'pipe', 'pipe'],
         timeout,
+        env: cleanEnv,
       });
 
       let stdout = '';

src/utils/shell-executor.ts

@@ -84,6 +84,10 @@ export function execClaude(
     ? { ...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;
+
   // propagate key env vars to tmux session so agent team teammates
   // (spawned via tmux split-window) inherit the correct config dir
   if (process.env.TMUX && envVars) {