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/foreach_control/component.contract.yaml

@@ -0,0 +1,56 @@
+canonical_id: "foreach_control"
+display_name: "迴圈控制"
+category: "logic"
+version: "v1"
+wasi_target: "preview1"
+stability: "floating"
+runtime_compat:
+  - "cf-workers"
+  - "workerd"
+  - "wazero"
+constraints:
+  max_size_kb: 2048
+  max_cold_start_ms: 50
+  no_network_syscall: true
+  no_filesystem_syscall: true
+  io_model: "stdin_stdout_json"
+input_schema:
+  type: object
+  required: [items]
+  properties:
+    items:
+      type: array
+      description: 要迭代的陣列
+    item_key:
+      type: string
+      description: 每個元素注入的變數名，預設 item
+output_schema:
+  type: object
+  properties:
+    success:
+      type: boolean
+    data:
+      type: object
+      properties:
+        items:
+          type: array
+        count:
+          type: number
+        current_index:
+          type: number
+        current_item: {}
+        item_key:
+          type: string
+gherkin_tests:
+  - scenario: "正常迭代"
+    given: '{"items":[1,2,3],"item_key":"item"}'
+    then_contains: '"current_index":0'
+  - scenario: "空陣列"
+    given: '{"items":[]}'
+    then_contains: '{"success":false'
+tags: [builtin, control, foreach, loop, iteration]
+description: "輸出第一個元素供 Cypher Executor 迭代，current_index 從 0 開始。"
+config_example: |
+  my_loop:                         # 節點名稱（可自訂）
+    items: "{{upstream.results}}"  # 要迭代的陣列（必填）
+    item_key: item                 # 每個元素注入的變數名，預設 item（選填）

registry/components/foreach_control/go.mod

@@ -0,0 +1,3 @@
+module component
+
+go 1.21

registry/components/foreach_control/main.go

@@ -0,0 +1,55 @@
+// foreach_control — 輸出第一個元素，Cypher Executor 負責迭代
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+type Input struct {
+	Items   []json.RawMessage `json:"items"`
+	ItemKey string            `json:"item_key"`
+}
+
+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
+	}
+	if len(input.Items) == 0 {
+		writeError("items 不能為空")
+		return
+	}
+
+	itemKey := input.ItemKey
+	if itemKey == "" {
+		itemKey = "item"
+	}
+
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data": map[string]interface{}{
+			"items":         input.Items,
+			"count":         len(input.Items),
+			"current_index": 0,
+			"current_item":  input.Items[0],
+			"item_key":      itemKey,
+		},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}