diff --git a/tests/test_workmux_add/test_named_agents.py b/tests/test_workmux_add/test_named_agents.py
index 64009535..fdf0d9f5 100644
--- a/tests/test_workmux_add/test_named_agents.py
+++ b/tests/test_workmux_add/test_named_agents.py
@@ -1,5 +1,6 @@
 """Tests for known agent auto-detection and prompt injection."""
 
+import os
 import shlex
 from pathlib import Path
 
@@ -13,6 +14,15 @@
 from .conftest import add_branch_and_get_worktree
 
 
+def _write_rc_with_fake_path(env: MuxEnvironment, bin_dir: Path) -> None:
+    """Write a shell RC file that prepends the fake agent bin dir to PATH."""
+    shell = os.environ.get("SHELL", "/bin/zsh")
+    rc_filename = ".zshrc" if "zsh" in shell else ".bashrc"
+    rc_path = env.home_path / rc_filename
+    rc_path.parent.mkdir(parents=True, exist_ok=True)
+    rc_path.write_text(f'export PATH="{bin_dir}:$PATH"\n')
+
+
 class TestKnownAgentAutoDetection:
     """Tests that literal known agent commands auto-detect for prompt injection."""
 
@@ -37,6 +47,9 @@ def test_literal_known_agent_gets_prompt_injection(
 """,
         )
 
+        # Write RC file so new panes find the fake agent on PATH
+        _write_rc_with_fake_path(env, fake_agent_installer.bin_dir)
+
         # Use literal "claude" in panes -- no <agent:> placeholder, no global agent
         write_workmux_config(
             mux_repo_path,
@@ -96,6 +109,9 @@ def test_two_known_agents_each_get_prompt(
 """,
         )
 
+        # Write RC file so new panes find the fake agents on PATH
+        _write_rc_with_fake_path(env, fake_agent_installer.bin_dir)
+
         write_workmux_config(
             mux_repo_path,
             panes=[