add black-box debug harness

cmd/patterm/debug_harness.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/hjbdev/patterm/internal/harness"
+)
+
+func runDebugHarness() {
+	var (
+		scenarioPath = flag.String("scenario", "", "JSON scenario path")
+		pattermBin   = flag.String("patterm-bin", "", "patterm binary under test (default: this executable)")
+	)
+	flag.Parse()
+	if *scenarioPath == "" {
+		die("debug-harness: --scenario is required")
+	}
+	if *pattermBin == "" {
+		exe, err := os.Executable()
+		if err != nil {
+			die("debug-harness: os.Executable: %v", err)
+		}
+		*pattermBin = exe
+	}
+	sc, err := harness.LoadScenario(*scenarioPath)
+	if err != nil {
+		fmt.Fprintf(os.Stdout, "{\"ok\":false,\"error\":%q}\n", err.Error())
+		os.Exit(2)
+	}
+	enc := json.NewEncoder(os.Stdout)
+	res, err := harness.RunScenario(harness.Options{
+		Scenario:   sc,
+		PattermBin: *pattermBin,
+	}, func(ev harness.Event) {
+		_ = enc.Encode(ev)
+	})
+	_ = enc.Encode(res)
+	if err != nil {
+		if res.Steps == 0 {
+			os.Exit(2)
+		}
+		os.Exit(1)
+	}
+}

cmd/patterm/main.go

@@ -7,6 +7,8 @@
 //	patterm mcp-stdio --socket S --identity I
 //	                             internal: stdio MCP proxy spawned for
 //	                             children, forwards JSON-RPC over S
+//	patterm debug-harness --scenario S
+//	                             internal: run a black-box harness scenario
 package main
 
 import (
@@ -30,6 +32,11 @@ func main() {
 		runMCPProxy()
 		return
 	}
+	if len(os.Args) >= 2 && os.Args[1] == "debug-harness" {
+		os.Args = append(os.Args[:1], os.Args[2:]...)
+		runDebugHarness()
+		return
+	}
 
 	var projectDir = flag.String("project", "", "project directory (default $PWD)")
 	flag.Parse()