Sim scaffold: cmd/expedition-sim drives synthetic expeditions

SimRunner re-uses production plugin code paths against a fresh sqlite DB —
SendDM no-ops without a Matrix client, so ground truth comes from the DB.
BuildCharacter persists adv+dnd character rows with class-appropriate
ability scores and spell slots; RunExpedition loops !expedition run with
stall detection until the autopilot halts or the expedition closes.

The cmd binary is a thin orchestrator: one flag-driven run, JSON output.
Per-room structured logging, day-cycle fast-forward, and matrix batching
are next session.

cmd/expedition-sim/main.go

@@ -0,0 +1,80 @@
+// expedition-sim drives synthetic players through expeditions for batch
+// analysis. Re-uses production plugin paths against a fresh sqlite DB so
+// outcomes mirror what live players hit.
+//
+// Usage: expedition-sim [-class fighter] [-level 5] [-zone goblin_warrens]
+//                       [-bank 1000] [-cap 200] [-data DIR]
+//
+// Defaults run one L5 fighter through goblin_warrens and print a JSON
+// SimResult to stdout. Per-room logs and matrix-mode batches land in a
+// follow-up; this binary is the scaffold the analysis stack hangs off.
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+
+	"gogobee/internal/plugin"
+
+	"maunium.net/go/mautrix/id"
+)
+
+func main() {
+	var (
+		class   = flag.String("class", "fighter", "DnD class id (fighter, mage, cleric, …)")
+		level   = flag.Int("level", 5, "character level")
+		zone    = flag.String("zone", "goblin_warrens", "zone id (see internal/plugin/dnd_zone_registry.go)")
+		bank    = flag.Float64("bank", 1000, "starting coin balance — must cover outfitting")
+		cap     = flag.Int("cap", 200, "max !expedition run invocations per expedition")
+		dataDir = flag.String("data", "", "data dir for the temp sqlite db (default: OS tempdir)")
+		userTag = flag.String("user", "@sim:expedition", "synthetic user id")
+	)
+	flag.Parse()
+
+	dir := *dataDir
+	if dir == "" {
+		var err error
+		dir, err = os.MkdirTemp("", "expedition-sim-")
+		if err != nil {
+			fail("mkdir temp:", err)
+		}
+		defer os.RemoveAll(dir)
+	}
+
+	runner, err := plugin.NewSimRunner(dir)
+	if err != nil {
+		fail("init runner:", err)
+	}
+	defer runner.Close()
+
+	uid := id.UserID(*userTag)
+	if _, err := runner.BuildCharacter(uid, plugin.DnDClass(*class), *level); err != nil {
+		fail("build character:", err)
+	}
+
+	runner.Euro.Credit(uid, *bank, "expedition-sim bankroll")
+
+	res, err := runner.RunExpedition(uid, plugin.ZoneID(*zone), *cap)
+	if err != nil {
+		// RunExpedition returns a partial result alongside the error so the
+		// outcome of a partial run is still observable.
+		if res != nil {
+			emit(res)
+		}
+		fail("run expedition:", err)
+	}
+	emit(res)
+}
+
+func emit(res *plugin.SimResult) {
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	_ = enc.Encode(res)
+}
+
+func fail(args ...interface{}) {
+	fmt.Fprintln(os.Stderr, args...)
+	os.Exit(1)
+}