fix(debug): handle mapping edges, stray traps and dying debuggees

Assisted-by: GLM 5.3

debug/target_linux_riscv64.go

@@ -17,8 +17,19 @@ import (
 	"sourcedock.dev/petrbalvin/gasm-sdk/verify"
 )
 
-// RunTarget is the debuggee entry point (gasm debug --target).
+// RunTarget is the debuggee entry point (gasm debug --target).  A failure
+// is marked in the handshake directory before the process exits, so the
+// debugger's readiness poll fails fast on a dead debuggee instead of
+// waiting out its whole budget.
 func RunTarget(asmPath, funcName, argsFile, tmpDir string) error {
+	err := runTarget(asmPath, funcName, argsFile, tmpDir)
+	if err != nil {
+		markDead(tmpDir, err.Error())
+	}
+	return err
+}
+
+func runTarget(asmPath, funcName, argsFile, tmpDir string) error {
 	src, err := os.ReadFile(asmPath)
 	if err != nil {
 		return fmt.Errorf("debug target: %w", err)