fix Linux daemon PID lookup without lsof

hindsight-embed/hindsight_embed/daemon_embed_manager.py

@@ -327,10 +327,8 @@ def _is_port_in_use(port: int) -> bool:
     @staticmethod
     def _find_pid_on_port(port: int) -> int | None:
         """Find the PID of the process listening on a port."""
-        import platform
-
-        try:
-            if platform.system() == "Windows":
+        if platform.system() == "Windows":
+            try:
                 # Use netstat on Windows
                 create_no_window = getattr(subprocess, "CREATE_NO_WINDOW", 0)
                 result = subprocess.run(
@@ -344,8 +342,11 @@ def _find_pid_on_port(port: int) -> int | None:
                     for line in result.stdout.splitlines():
                         if f"127.0.0.1:{port}" in line and "LISTENING" in line:
                             return int(line.strip().split()[-1])
-            else:
-                # Use lsof on macOS/Linux
+            except (subprocess.TimeoutExpired, ValueError, OSError):
+                return None
+        else:
+            try:
+                # lsof is available by default on macOS and common on Linux.
                 result = subprocess.run(
                     ["lsof", "-ti", f":{port}", "-sTCP:LISTEN"],
                     capture_output=True,
@@ -354,8 +355,24 @@ def _find_pid_on_port(port: int) -> int | None:
                 )
                 if result.returncode == 0 and result.stdout.strip():
                     return int(result.stdout.strip().split()[0])
-        except (subprocess.TimeoutExpired, ValueError, OSError, FileNotFoundError):
-            pass
+            except (subprocess.TimeoutExpired, ValueError, OSError):
+                pass
+
+            if platform.system() == "Linux":
+                try:
+                    # Minimal Linux installations may provide ss but not lsof.
+                    result = subprocess.run(
+                        ["ss", "-H", "-ltnp", f"sport = :{port}"],
+                        capture_output=True,
+                        text=True,
+                        timeout=5,
+                    )
+                    if result.returncode == 0:
+                        match = re.search(r"\bpid=(\d+)\b", result.stdout)
+                        if match:
+                            return int(match.group(1))
+                except (subprocess.TimeoutExpired, ValueError, OSError):
+                    pass
         return None
 
     @staticmethod

hindsight-embed/tests/test_embed_manager.py

@@ -384,6 +384,29 @@ def fake_run(*args, **kwargs):
     assert calls[0][1]["creationflags"] == 0x08000000
 
 
+def test_find_pid_on_port_linux_falls_back_to_ss(monkeypatch):
+    calls = []
+
+    def fake_run(command, **kwargs):
+        calls.append(command)
+        if command[0] == "lsof":
+            raise FileNotFoundError
+
+        result = MagicMock()
+        result.returncode = 0
+        result.stdout = 'LISTEN 0 4096 127.0.0.1:9177 0.0.0.0:* users:(("hindsight-api",pid=15774,fd=19))\n'
+        return result
+
+    monkeypatch.setattr("hindsight_embed.daemon_embed_manager.platform.system", lambda: "Linux")
+    monkeypatch.setattr("hindsight_embed.daemon_embed_manager.subprocess.run", fake_run)
+
+    assert DaemonEmbedManager._find_pid_on_port(9177) == 15774
+    assert calls == [
+        ["lsof", "-ti", ":9177", "-sTCP:LISTEN"],
+        ["ss", "-H", "-ltnp", "sport = :9177"],
+    ]
+
+
 def test_stop_ui_kills_recorded_and_configured_ports(tmp_path, monkeypatch):
     """After a UI-port change, stop_ui must kill BOTH the recorded (old, actually
     running) port and the configured (new) port — otherwise the old UI orphans."""