Fix Windows build: extract Unix-only signals behind build tags

syscall.SIGTSTP and syscall.SIGCONT don't exist on Windows, causing
the GoReleaser Windows build to fail. Extract signal calls into
platform-specific files using build tags.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bborn

internal/executor/codex_executor.go

@@ -295,7 +295,7 @@ func (c *CodexExecutor) Suspend(taskID int64) bool {
 		return false
 	}
 
-	if err := proc.Signal(syscall.SIGTSTP); err != nil {
+	if err := sendSIGTSTP(proc); err != nil {
 		c.logger.Debug("Failed to suspend process", "pid", pid, "error", err)
 		return false
 	}
@@ -331,7 +331,7 @@ func (c *CodexExecutor) ResumeProcess(taskID int64) bool {
 		return false
 	}
 
-	if err := proc.Signal(syscall.SIGCONT); err != nil {
+	if err := sendSIGCONT(proc); err != nil {
 		c.logger.Debug("Failed to resume process", "pid", pid, "error", err)
 		return false
 	}

internal/executor/executor.go

@@ -362,7 +362,7 @@ func (e *Executor) SuspendTask(taskID int64) bool {
 		return false
 	}
 
-	if err := proc.Signal(syscall.SIGTSTP); err != nil {
+	if err := sendSIGTSTP(proc); err != nil {
 		e.logger.Debug("Failed to suspend process", "pid", pid, "error", err)
 		return false
 	}
@@ -405,7 +405,7 @@ func (e *Executor) ResumeTask(taskID int64) bool {
 		return false
 	}
 
-	if err := proc.Signal(syscall.SIGCONT); err != nil {
+	if err := sendSIGCONT(proc); err != nil {
 		e.logger.Debug("Failed to resume process", "pid", pid, "error", err)
 		return false
 	}

internal/executor/gemini_executor.go

@@ -233,7 +233,7 @@ func (g *GeminiExecutor) Suspend(taskID int64) bool {
 		g.logger.Debug("Failed to find process", "pid", pid, "error", err)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGTSTP); err != nil {
+	if err := sendSIGTSTP(proc); err != nil {
 		g.logger.Debug("Failed to suspend process", "pid", pid, "error", err)
 		return false
 	}
@@ -264,7 +264,7 @@ func (g *GeminiExecutor) ResumeProcess(taskID int64) bool {
 		delete(g.suspendedTasks, taskID)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGCONT); err != nil {
+	if err := sendSIGCONT(proc); err != nil {
 		g.logger.Debug("Failed to resume process", "pid", pid, "error", err)
 		return false
 	}

internal/executor/openclaw_executor.go

@@ -257,7 +257,7 @@ func (o *OpenClawExecutor) Suspend(taskID int64) bool {
 		o.logger.Debug("Failed to find process", "pid", pid, "error", err)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGTSTP); err != nil {
+	if err := sendSIGTSTP(proc); err != nil {
 		o.logger.Debug("Failed to suspend process", "pid", pid, "error", err)
 		return false
 	}
@@ -288,7 +288,7 @@ func (o *OpenClawExecutor) ResumeProcess(taskID int64) bool {
 		delete(o.suspendedTasks, taskID)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGCONT); err != nil {
+	if err := sendSIGCONT(proc); err != nil {
 		o.logger.Debug("Failed to resume process", "pid", pid, "error", err)
 		return false
 	}

internal/executor/opencode_executor.go

@@ -250,7 +250,7 @@ func (o *OpenCodeExecutor) Suspend(taskID int64) bool {
 		o.logger.Debug("Failed to find process", "pid", pid, "error", err)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGTSTP); err != nil {
+	if err := sendSIGTSTP(proc); err != nil {
 		o.logger.Debug("Failed to suspend process", "pid", pid, "error", err)
 		return false
 	}
@@ -281,7 +281,7 @@ func (o *OpenCodeExecutor) ResumeProcess(taskID int64) bool {
 		delete(o.suspendedTasks, taskID)
 		return false
 	}
-	if err := proc.Signal(syscall.SIGCONT); err != nil {
+	if err := sendSIGCONT(proc); err != nil {
 		o.logger.Debug("Failed to resume process", "pid", pid, "error", err)
 		return false
 	}

internal/executor/signal_unix.go

@@ -0,0 +1,16 @@
+//go:build !windows
+
+package executor
+
+import (
+	"os"
+	"syscall"
+)
+
+func sendSIGTSTP(proc *os.Process) error {
+	return proc.Signal(syscall.SIGTSTP)
+}
+
+func sendSIGCONT(proc *os.Process) error {
+	return proc.Signal(syscall.SIGCONT)
+}

internal/executor/signal_windows.go

@@ -0,0 +1,16 @@
+//go:build windows
+
+package executor
+
+import (
+	"fmt"
+	"os"
+)
+
+func sendSIGTSTP(_ *os.Process) error {
+	return fmt.Errorf("suspend not supported on Windows")
+}
+
+func sendSIGCONT(_ *os.Process) error {
+	return fmt.Errorf("resume not supported on Windows")
+}