fix(windows): daemon stop/kill now uses proper Windows API (GH#992)

On Windows, the daemon stop command was failing with "exit status 1" because
`taskkill` without `/F` flag does not work for console processes that do not
have windows to receive close messages.

Changes:
- Use `os.Process.Kill()` which calls Windows `TerminateProcess` API
- This is the reliable way to terminate processes on Windows
- The graceful RPC shutdown is already attempted before falling back to kill
- Updated error messages to be platform-agnostic (removed SIGTERM/SIGKILL)

The fix uses Go cross-platform process APIs instead of shelling out to
external commands, which is more reliable and portable.

Closes #992

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/daemon/discovery.go

@@ -411,9 +411,9 @@ func stopDaemonWithTimeout(daemon DaemonInfo) error {
 		}
 	}
 
-	// Try SIGTERM with 3 second timeout
+	// Try graceful kill with 3 second timeout
 	if err := killProcess(daemon.PID); err != nil {
-		return fmt.Errorf("SIGTERM failed: %w", err)
+		return fmt.Errorf("kill process failed: %w", err)
 	}
 
 	// Wait up to 3 seconds for process to die
@@ -424,9 +424,9 @@ func stopDaemonWithTimeout(daemon DaemonInfo) error {
 		}
 	}
 
-	// SIGTERM timeout, try SIGKILL with 1 second timeout
+	// Graceful kill timeout, try force kill with 1 second timeout
 	if err := forceKillProcess(daemon.PID); err != nil {
-		return fmt.Errorf("SIGKILL failed: %w", err)
+		return fmt.Errorf("force kill failed: %w", err)
 	}
 
 	// Wait up to 1 second for process to die
@@ -437,5 +437,5 @@ func stopDaemonWithTimeout(daemon DaemonInfo) error {
 		}
 	}
 
-	return fmt.Errorf("process %d did not die after SIGKILL", daemon.PID)
+	return fmt.Errorf("process %d did not die after force kill", daemon.PID)
 }

internal/daemon/kill_windows.go

@@ -3,45 +3,70 @@
 package daemon
 
 import (
-	"bytes"
 	"fmt"
+	"os"
 	"os/exec"
-	"strconv"
 )
 
 func killProcess(pid int) error {
-	// Use taskkill on Windows (without /F for graceful)
-	cmd := exec.Command("taskkill", "/PID", strconv.Itoa(pid))
-	if err := cmd.Run(); err != nil {
+	// On Windows, there's no SIGTERM equivalent for console processes.
+	// The graceful RPC shutdown is already attempted before this function is called.
+	// Use os.Process.Kill() which calls TerminateProcess - the reliable Windows API.
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		return fmt.Errorf("failed to find process %d: %w", pid, err)
+	}
+	if err := proc.Kill(); err != nil {
 		return fmt.Errorf("failed to kill PID %d: %w", pid, err)
 	}
 	return nil
 }
 
 func forceKillProcess(pid int) error {
-	// Use taskkill with /F flag for force kill
-	cmd := exec.Command("taskkill", "/PID", strconv.Itoa(pid), "/F")
-	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("failed to force kill PID %d: %w", pid, err)
-	}
-	return nil
+	// On Windows, Kill() already uses TerminateProcess which is forceful
+	return killProcess(pid)
 }
 
 func isProcessAlive(pid int) bool {
-	// Use tasklist to check if process exists
+	// On Windows, FindProcess always succeeds, but we can check if the process
+	// is actually running by trying to get its exit code via Wait with WNOHANG.
+	// A simpler approach: try to open the process and check for errors.
+	proc, err := os.FindProcess(pid)
+	if err != nil {
+		return false
+	}
+	// On Windows, we need to actually check if the process exists.
+	// Signal(nil) on Windows returns an error if process doesn't exist.
+	// However, os.Process.Signal is not implemented on Windows.
+	// Use a different approach: try to kill with signal 0 equivalent.
+	// Actually, on Windows we can check via process handle opening.
+	// The simplest reliable way is to use tasklist.
+	//
+	// Note: os.FindProcess on Windows always succeeds regardless of whether
+	// the process exists. We need to actually try to interact with it.
+	// Using Release() and checking the error doesn't work either.
+	//
+	// Fall back to tasklist for reliability.
+	return isProcessAliveTasklist(pid, proc)
+}
+
+func isProcessAliveTasklist(pid int, _ *os.Process) bool {
+	// Use Windows API via tasklist to check if process exists
+	// This is the most reliable method on Windows
 	cmd := exec.Command("tasklist", "/FI", fmt.Sprintf("PID eq %d", pid), "/NH")
 	output, err := cmd.Output()
 	if err != nil {
 		return false
 	}
-	// Check if output contains the PID
-	return contains(string(output), strconv.Itoa(pid))
+	// Check if output contains the PID (tasklist returns "INFO: No tasks..." if not found)
+	return containsSubstring(string(output), fmt.Sprintf("%d", pid))
 }
 
-func contains(s, substr string) bool {
-	return findSubstring(s, substr)
-}
-
-func findSubstring(s, substr string) bool {
-	return len(s) >= len(substr) && bytes.Contains([]byte(s), []byte(substr))
+func containsSubstring(s, substr string) bool {
+	for i := 0; i <= len(s)-len(substr); i++ {
+		if s[i:i+len(substr)] == substr {
+			return true
+		}
+	}
+	return false
 }