arcrun — AI workflow execution engine (clean history)

Self-hosted 開源：WASM 零件 + recipe + cypher-executor，跑在你自己的 Cloudflare。

此為重建的乾淨歷史起點（移除曾誤 commit 的 GCP SA 金鑰，舊歷史保留在
richblack/arcrun 與本地 backup 分支）。含：
- acr init --self-hosted installer（建 KV/R2 + codeload 拉預編譯 wasm + wrangler deploy + seed recipe）
- recipe push 把關（資料外流提醒 + 打通檢查）
- 19 個正當零件預編譯 wasm（claude_api/km_writer/kbdb_upsert_block 排除：違反 DECISIONS §1）
- CLI / cypher-executor / registry / 完整 SDD

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

registry/components/switch/main.go

@@ -0,0 +1,61 @@
+// switch — 依值路由到對應分支
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+type Case struct {
+	Match  string `json:"match"`
+	Branch string `json:"branch"`
+}
+
+type Input struct {
+	Value         string `json:"value"`
+	Cases         []Case `json:"cases"`
+	DefaultBranch string `json:"default_branch"`
+}
+
+func main() {
+	raw, err := io.ReadAll(os.Stdin)
+	if err != nil {
+		writeError("failed to read stdin: " + err.Error())
+		return
+	}
+	var input Input
+	if err := json.Unmarshal(raw, &input); err != nil {
+		writeError("invalid input JSON: " + err.Error())
+		return
+	}
+
+	for _, c := range input.Cases {
+		if c.Match == input.Value {
+			writeSuccess(c.Branch)
+			return
+		}
+	}
+
+	branch := input.DefaultBranch
+	if branch == "" {
+		branch = "default"
+	}
+	writeSuccess(branch)
+}
+
+func writeSuccess(branch string) {
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data":    map[string]interface{}{"branch": branch},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}