M2: wire planning coach backend into the daemon with graceful fallback

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/antidriftd/main.go

@@ -5,10 +5,12 @@ package main
 import (
 	"context"
 	"log"
+	"os"
 	"os/exec"
 	"runtime"
 	"time"
 
+	"antidrift/internal/ai"
 	"antidrift/internal/evidence"
 	"antidrift/internal/session"
 	"antidrift/internal/store"
@@ -30,6 +32,16 @@ func main() {
 	srv := web.NewServer(ctrl)
 	srv.Init() // re-arm or expire a restored Active session
 
+	// Wire the AI planning coach. Backend selectable via ANTIDRIFT_AI_BACKEND
+	// (claude default, or codex). Misconfiguration degrades to no coach rather
+	// than failing startup — manual planning still works.
+	if backend, err := ai.NewBackend(os.Getenv("ANTIDRIFT_AI_BACKEND")); err != nil {
+		log.Printf("ai coach disabled: %v", err)
+	} else {
+		ctrl.SetCoach(ai.NewService(backend))
+		log.Printf("ai coach: %s backend", backend.Name())
+	}
+
 	src := evidence.NewSource()
 	go src.Watch(context.Background(), ctrl.RecordWindow)