diff --git a/tests/e2e/test_titles.py b/tests/e2e/test_titles.py
index 82d0afb..a380147 100644
--- a/tests/e2e/test_titles.py
+++ b/tests/e2e/test_titles.py
@@ -123,6 +123,9 @@ class Titles(harness.FrameTestCase):
         self.assertFalse(run['started'])
         self.assertEqual(run['message'], f'Tool 4183110 "Steam Linux Runtime 4.0" is found for appID {appid}, '
                                          'but is not installed')
+        # The headset smoke test finds this in Steam's logs, where compat_log.txt has
+        # binary bytes in it: only grep -a returns the line (Frame, 2026-09-27).
+        self.assertIn(run['message'], ssh('grep -arshF "but is not installed" ~/.local/share/Steam/logs/'))
         # With the runtime installed, it starts.
         ctl('runtime', 'SteamLinuxRuntime_4', 'installed')
         ok('POST', '/api/titles', {'action': 'launch', 'id': 'Tiny_PC_Game'})
diff --git a/tests/fakeframe/rootfs/usr/local/lib/fakeframe/fakesteam.py b/tests/fakeframe/rootfs/usr/local/lib/fakeframe/fakesteam.py
index c7adcc0..7c9ee78 100755
--- a/tests/fakeframe/rootfs/usr/local/lib/fakeframe/fakesteam.py
+++ b/tests/fakeframe/rootfs/usr/local/lib/fakeframe/fakesteam.py
@@ -40,6 +40,10 @@ HOME = fs.HOME
 STEAM_DIR = HOME + '/.steam'
 PID_FILE, TOKEN_FILE, PIPE = (f'{STEAM_DIR}/steam.{n}' for n in ('pid', 'token', 'pipe'))
 CONSOLE_LOG = fs.STEAM_ROOT + '/logs/console_log.txt'  # guess: which file Steam logs devkit launches to
+# Steam logs compat tool lookups here, and on the Frame the file has binary bytes
+# in it, so plain grep only says "binary file matches" (headset smoke test,
+# 2026-09-27, BUILD_ID 20260922.6101926). The fake starts it with a NUL to match.
+COMPAT_LOG = fs.STEAM_ROOT + '/logs/compat_log.txt'
 DEVTOOLS_PORT = 8080
 TARGET_ID = 'F0CA11ED5EA4ED0000000000000000AB'
 GAME_LOGS = '/var/log/fakeframe'
@@ -67,6 +71,14 @@ def console(line):
         f.write(time.strftime('[%Y-%m-%d %H:%M:%S] ') + line + '\n')
 
 
+def compat(line):
+    os.makedirs(os.path.dirname(COMPAT_LOG), exist_ok=True)
+    with open(COMPAT_LOG, 'ab') as f:
+        if f.tell() == 0:
+            f.write(b'\0\n')
+        f.write((time.strftime('[%Y-%m-%d %H:%M:%S] ') + line + '\n').encode())
+
+
 def respond(path, text=None, error=None):
     """Answer a devkit request the way devkit_utils.wait_on_file_response expects."""
     lock = path + '.lock'
@@ -210,6 +222,7 @@ def cmd_run_game(q):
         name = fs.RUNTIME_NAMES.get(tool, tool)
         record.update(started=False, message=f'Tool {fs.RUNTIME_APPIDS.get(tool, 0)} "{name}" is found for '
                                               f'appID {game["appid"]}, but is not installed')
+        compat(record['message'])
     elif tool and tool.startswith('proton'):
         # How Steam ran a sideloaded .exe on the Frame (docs/sideloading.md).
         prefix = f"{fs.STEAM_ROOT}/steamapps/compatdata/{game['appid']}/pfx"
diff --git a/tests/smoke/frame_smoke.py b/tests/smoke/frame_smoke.py
index 14e8ff0..740e048 100644
--- a/tests/smoke/frame_smoke.py
+++ b/tests/smoke/frame_smoke.py
@@ -115,9 +115,13 @@ def status(build):
 
 
 def steam_log_lines(*patterns):
-    """Steam log lines holding any of the fixed strings (which files: not verified, so all)."""
+    """Steam log lines holding any of the fixed strings (which files: not verified, so all).
+
+    -a: compat_log.txt has binary bytes in it, and without it grep only says
+    "binary file matches" (seen on the Frame, 2026-09-27).
+    """
     pats = ' '.join(f'-e {shlex.quote(p)}' for p in patterns)
-    out = ssh(f"grep -rshF {pats} ~/.local/share/Steam/logs/ 2>/dev/null || true")
+    out = ssh(f"grep -arshF {pats} ~/.local/share/Steam/logs/ 2>/dev/null || true")
     return out.strip().splitlines()