diff --git a/CLAUDE.md b/CLAUDE.md
index 280a6fab..ac1f3e90 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -35,7 +35,7 @@ When user says "COM":
 1. Increment version in BOTH `package.json` AND `CLAUDE.md` (verify they match with `grep version package.json && grep Version CLAUDE.md`)
 2. Run: `git add -A && git commit -m "chore: bump version to X.XXXX" && git push && npm run build && systemctl --user restart claudeman-web`
 
-**Version**: 0.1557 (must match `package.json` for npm publish)
+**Version**: 0.1558 (must match `package.json` for npm publish)
 
 ## Project Overview
 
@@ -63,9 +63,9 @@ npx tsx src/index.ts web --https   # With TLS (only needed for remote access)
 npm run typecheck                  # Type check
 tsc --noEmit --watch               # Continuous type checking
 
-# Testing
-npx vitest run                     # All tests
-npx vitest run test/<file>.test.ts # Single file
+# Testing (NEVER run full suite from inside Claudeman — kills tmux sessions)
+# npx vitest run                   # ALL tests — DANGEROUS inside Claudeman
+npx vitest run test/<file>.test.ts # Single file (SAFE)
 npx vitest run -t "pattern"        # Tests matching name
 npm run test:coverage              # With coverage report
 
diff --git a/package.json b/package.json
index e05b294c..cf3960cd 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "claudeman",
-  "version": "0.1557",
+  "version": "0.1558",
   "description": "The missing control plane for Claude Code - run 20 autonomous agents with real-time monitoring and session persistence",
   "type": "module",
   "main": "dist/index.js",
diff --git a/src/mux-interface.ts b/src/mux-interface.ts
index 19f7e7d2..9b206638 100644
--- a/src/mux-interface.ts
+++ b/src/mux-interface.ts
@@ -155,4 +155,7 @@ export interface TerminalMultiplexer extends EventEmitter {
 
   /** Check if the multiplexer binary is available on the system */
   isAvailable(): boolean;
+
+  /** Check if a multiplexer session actually exists (process-level check, not just tracked) */
+  muxSessionExists(muxName: string): boolean;
 }
diff --git a/src/session.ts b/src/session.ts
index ef0616cb..9cd28065 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -849,6 +849,12 @@ export class Session extends EventEmitter {
     // If mux wrapping is enabled, create or attach to a mux session
     if (this._useMux && this._mux) {
       try {
+        // Verify stale mux session — tmux destroys session when command exits
+        // (remain-on-exit is off), but _muxSession reference persists
+        if (this._muxSession && !this._mux.muxSessionExists(this._muxSession.muxName)) {
+          console.log('[Session] Stale mux session detected (tmux gone):', this._muxSession.muxName);
+          this._muxSession = null;
+        }
         // Check if we already have a mux session (restored session)
         const isRestoredSession = this._muxSession !== null;
         if (isRestoredSession) {
@@ -1128,6 +1134,11 @@ export class Session extends EventEmitter {
     // If mux wrapping is enabled, create or attach to a mux session
     if (this._useMux && this._mux) {
       try {
+        // Verify stale mux session — tmux destroys session when command exits
+        if (this._muxSession && !this._mux.muxSessionExists(this._muxSession.muxName)) {
+          console.log('[Session] Stale mux session detected (tmux gone):', this._muxSession.muxName);
+          this._muxSession = null;
+        }
         // Check if we already have a mux session (restored session)
         const isRestoredSession = this._muxSession !== null;
         if (isRestoredSession) {
diff --git a/src/tmux-manager.ts b/src/tmux-manager.ts
index a79502c9..92ebf4bc 100644
--- a/src/tmux-manager.ts
+++ b/src/tmux-manager.ts
@@ -348,6 +348,10 @@ export class TmuxManager extends EventEmitter implements TerminalMultiplexer {
   /**
    * Check if a tmux session exists.
    */
+  muxSessionExists(muxName: string): boolean {
+    return this.sessionExists(muxName);
+  }
+
   private sessionExists(muxName: string): boolean {
     if (IS_TEST_MODE) return false;