diff --git a/Dockerfile b/Dockerfile
index b56a1a68634..77ded4c1ed8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -33,20 +33,24 @@ ARG OPENCLAW_2026_5_22_INTEGRITY=sha512-m+zgBELGbCHjWB1IWF5WSWNPr480cMKOMff2OF72
 
 # Harden: remove unnecessary build tools and network probes from base image (#830)
 # Protect runtime tools before autoremove — the GHCR base may predate the
-# procps/e2fsprogs additions, leaving ps/chattr absent or auto-marked. The
-# conditional install keeps stale bases usable while fresh bases skip apt.
-# Refs: #2343, shields-up chattr hardening
+# procps/e2fsprogs/tmux additions, leaving ps/chattr/tmux absent or auto-marked.
+# The conditional install keeps stale bases usable while fresh bases skip apt.
+# tmux is required by OpenClaw's bundled tmux-session flow (#4513); a stale base
+# without it makes that flow fail with `tmux: command not found`.
+# Refs: #2343, #4513, shields-up chattr hardening
 # hadolint ignore=DL3001
 RUN set -eu; \
-    apt-mark manual procps e2fsprogs 2>/dev/null || true; \
+    apt-mark manual procps e2fsprogs tmux 2>/dev/null || true; \
     (apt-get remove --purge -y gcc gcc-12 g++ g++-12 cpp cpp-12 make \
         netcat-openbsd netcat-traditional ncat 2>/dev/null || true); \
     apt-get autoremove --purge -y; \
     needs_ps=0; \
     needs_chattr=0; \
+    needs_tmux=0; \
     if ! command -v ps >/dev/null 2>&1; then needs_ps=1; fi; \
     if ! command -v chattr >/dev/null 2>&1; then needs_chattr=1; fi; \
-    if [ "$needs_ps" = "1" ] || [ "$needs_chattr" = "1" ]; then \
+    if ! command -v tmux >/dev/null 2>&1; then needs_tmux=1; fi; \
+    if [ "$needs_ps" = "1" ] || [ "$needs_chattr" = "1" ] || [ "$needs_tmux" = "1" ]; then \
         apt-get update; \
         if [ "$needs_ps" = "1" ]; then \
             apt-get install -y --no-install-recommends procps=2:4.0.4-9; \
@@ -54,10 +58,14 @@ RUN set -eu; \
         if [ "$needs_chattr" = "1" ]; then \
             apt-get install -y --no-install-recommends e2fsprogs=1.47.2-3+b11; \
         fi; \
+        if [ "$needs_tmux" = "1" ]; then \
+            apt-get install -y --no-install-recommends tmux=3.5a-3; \
+        fi; \
     fi; \
     rm -rf /var/lib/apt/lists/*; \
     ps --version; \
-    command -v chattr >/dev/null
+    command -v chattr >/dev/null; \
+    command -v tmux >/dev/null
 
 
 # Copy built plugin and blueprint into the sandbox
diff --git a/Dockerfile.base b/Dockerfile.base
index fdd34790c7b..3d38d98607c 100644
--- a/Dockerfile.base
+++ b/Dockerfile.base
@@ -68,6 +68,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         jq=1.7.1-6+deb13u2 \
         vim-tiny=2:9.1.1230-2 \
         openssh-sftp-server=1:10.0p1-7+deb13u4 \
+        tmux=3.5a-3 \
     && rm -rf /var/lib/apt/lists/* \
     && ln -s /usr/bin/python3 /usr/local/bin/python
 
diff --git a/test/e2e/test-sandbox-operations.sh b/test/e2e/test-sandbox-operations.sh
index 0e9f3d3ec75..cc1549cda9a 100755
--- a/test/e2e/test-sandbox-operations.sh
+++ b/test/e2e/test-sandbox-operations.sh
@@ -452,6 +452,42 @@ test_sbx_04_log_streaming() {
   fi
 }
 
+# ── TC-SBX-09: Tmux Session Flow ────────────────────────────────────────────
+# OpenClaw's bundled tmux-session flow shells out to `tmux` inside the sandbox.
+# The sandbox image must ship tmux (issue #4513) or that flow fails with
+# `tmux: command not found`. Assert the binary is present and can drive a full
+# detached session lifecycle (new-session → list → kill), which is the exact
+# shape the bundled flow exercises.
+test_sbx_09_tmux_session_flow() {
+  log "=== TC-SBX-09: Tmux Session Flow ==="
+  require_sandbox "$SANDBOX_A" "TC-SBX-09" || return
+
+  local which_out
+  which_out=$(sandbox_exec "command -v tmux || echo TMUX_MISSING" 2>&1) || true
+  if echo "$which_out" | grep -q "TMUX_MISSING"; then
+    fail "TC-SBX-09: Tmux Session Flow" "tmux not found inside sandbox (issue #4513)"
+    return
+  fi
+  pass "TC-SBX-09: tmux is installed in the sandbox ($(echo "$which_out" | head -1))"
+
+  # Drive a detached session lifecycle the way the bundled flow does. tmux needs
+  # a writable socket dir; /tmp is on the sandbox write set.
+  local sess="nemoclaw-e2e-tmux-$$"
+  local flow_out
+  flow_out=$(sandbox_exec "TMUX_TMPDIR=/tmp tmux new-session -d -s '${sess}' 'sleep 30' \
+    && TMUX_TMPDIR=/tmp tmux list-sessions \
+    && TMUX_TMPDIR=/tmp tmux kill-session -t '${sess}' \
+    && echo TMUX_FLOW_OK" 2>&1) || true
+
+  if echo "$flow_out" | grep -q "TMUX_FLOW_OK" && echo "$flow_out" | grep -q "${sess}"; then
+    pass "TC-SBX-09: tmux new/list/kill session lifecycle works"
+  else
+    # Best-effort cleanup in case kill-session never ran.
+    sandbox_exec "TMUX_TMPDIR=/tmp tmux kill-session -t '${sess}' 2>/dev/null || true" >/dev/null 2>&1 || true
+    fail "TC-SBX-09: Tmux Session Flow" "Session lifecycle failed: $(echo "$flow_out" | head -5)"
+  fi
+}
+
 # =============================================================================
 # Phase 2: Non-destructive recovery (sandbox A stays alive)
 # =============================================================================
@@ -792,6 +828,7 @@ main() {
   test_sbx_02_connect_chat
   test_sbx_03_status_fields
   test_sbx_04_log_streaming
+  test_sbx_09_tmux_session_flow
 
   # Phase 2: Non-destructive recovery (sandbox A stays alive)
   test_sbx_07_registry_rebuild
diff --git a/test/runner.test.ts b/test/runner.test.ts
index ba22cebcb6e..3e2f16f9ed2 100644
--- a/test/runner.test.ts
+++ b/test/runner.test.ts
@@ -859,4 +859,48 @@ describe("regression guards", () => {
       expect(src).not.toContain("SKIP_VLLM=1");
     });
   });
+
+  describe("sandbox ships tmux for the bundled tmux-session flow (#4513)", () => {
+    const repoRoot = path.join(import.meta.dirname, "..");
+
+    it("base image installs a pinned tmux in the apt package list", () => {
+      const src = fs.readFileSync(path.join(repoRoot, "Dockerfile.base"), "utf-8");
+      // Pinned (DL3008) tmux must be part of the single base apt-get install
+      // layer so fresh builds ship it without a runtime apt round-trip.
+      expect(src).toMatch(/tmux=[0-9]/);
+    });
+
+    it("runtime image repairs tmux on stale bases and asserts it at build time", () => {
+      const src = fs.readFileSync(path.join(repoRoot, "Dockerfile"), "utf-8");
+      // Stale GHCR bases predating the tmux addition must still converge: the
+      // hardening layer detects a missing tmux, installs a pinned version, and
+      // fails the build if tmux is still absent afterwards.
+      expect(src).toContain("needs_tmux=1");
+      expect(src).toMatch(/apt-get install -y --no-install-recommends tmux=[0-9]/);
+      expect(src).toContain("command -v tmux >/dev/null");
+    });
+
+    it("base and runtime images pin tmux to the same version", () => {
+      const baseSrc = fs.readFileSync(path.join(repoRoot, "Dockerfile.base"), "utf-8");
+      const runtimeSrc = fs.readFileSync(path.join(repoRoot, "Dockerfile"), "utf-8");
+      const baseVersion = baseSrc.match(/tmux=([0-9][^\s\\]*)/)?.[1];
+      const runtimeVersion = runtimeSrc.match(
+        /apt-get install -y --no-install-recommends tmux=([0-9][^\s\\;]*)/,
+      )?.[1];
+      expect(baseVersion).toBeDefined();
+      expect(runtimeVersion).toBeDefined();
+      expect(runtimeVersion).toBe(baseVersion);
+    });
+
+    it("the e2e sandbox suite exercises the tmux-session flow", () => {
+      const src = fs.readFileSync(
+        path.join(repoRoot, "test", "e2e", "test-sandbox-operations.sh"),
+        "utf-8",
+      );
+      expect(src).toContain("test_sbx_09_tmux_session_flow");
+      expect(src).toContain("command -v tmux");
+      // The smoke must be wired into the run, not just defined.
+      expect(src).toMatch(/^\s*test_sbx_09_tmux_session_flow\s*$/m);
+    });
+  });
 });