feat(arcrun): implement arcrun MVP — open-source AI workflow engine

Phase 1-5 complete per .agents/specs/u6u-core-mvp/:

**Phase 1 — Cherry-pick & cleanup**
- Create arcrun/ from cypher-executor, credentials, builtins, registry
- Remove 9 InkStone Service Bindings (KBDB, REGISTRY, CLINIC_*, AICEO, MINI_ME)
- Rewrite component-loader: 3-layer (builtin → WASM_BUCKET R2 → error)
- Remove autoPublishMissing.ts, proxy.ts (AICEO), execution-logger.ts (KBDB)
- Clean all KV namespace IDs and InkStone internal URLs from config files

**Phase 2 — contract.yaml completeness**
- Add credentials_required to gmail, google_sheets, telegram, line_notify
- Add config_example to all 21 components with annotated field descriptions

**Phase 3 — Credential injection**
- Add credential-injector.ts: AES-GCM decrypt from CREDENTIALS_KV
- Integrate into GraphExecutor before WASM execution
- Structured errors with repair instructions when credential missing

**Phase 4 — CLI (acr)**
- cli/package.json: arcrun package, bin: acr, deps: commander/js-yaml/chalk/ora
- 8 commands: init, creds push, push, run, validate, parts, list, logs
- Standard mode: writes directly to user's CF KV via CF REST API
- acr init: interactive setup with arcrun.dev API Key registration

**Phase 5 — Open source release prep**
- README.md: 5-minute quickstart, component table, workflow YAML syntax
- CONTRIBUTING.md: TinyGo dev env, component scaffolding, submission flow
- Security audit: no InkStone internal URLs/IDs in committed files
- .gitignore: exclude credentials.yaml, .wrangler, *.wasm

https://claude.ai/code/session_01BnCdSLVH8tUed9VrrPavgT

registry/components/try_catch/component.contract.yaml

@@ -0,0 +1,53 @@
+canonical_id: "try_catch"
+display_name: "錯誤處理"
+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
+  properties:
+    result: {}
+    error:
+      type: string
+      description: 上游錯誤訊息，非空則走 catch 分支
+output_schema:
+  type: object
+  properties:
+    success:
+      type: boolean
+    data:
+      type: object
+      properties:
+        branch:
+          type: string
+          enum: [try, catch]
+        result: {}
+        error:
+          type: string
+gherkin_tests:
+  - scenario: "無錯誤走 try"
+    given: '{"result":{"value":42},"error":""}'
+    then_contains: '"branch":"try"'
+  - scenario: "有錯誤走 catch"
+    given: '{"result":null,"error":"something went wrong"}'
+    then_contains: '"branch":"catch"'
+  - scenario: "無效 JSON"
+    given: 'not-json'
+    then_contains: '{"success":false'
+tags: [builtin, control, try, catch, error, handling]
+description: "判斷上游結果是否有 error，決定走 try 或 catch 分支。"
+config_example: |
+  my_try_catch:                       # 節點名稱（可自訂）
+    result: "{{upstream.data}}"       # 上游回傳的結果，任意型別（選填）
+    error: "{{upstream.error}}"       # 上游錯誤訊息，非空則走 catch 分支（選填）

registry/components/try_catch/go.mod

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

registry/components/try_catch/main.go

@@ -0,0 +1,55 @@
+// try_catch — 判斷上游結果是否有 error，決定走 try 或 catch 分支
+//
+//go:build tinygo
+
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+)
+
+type Input struct {
+	Result json.RawMessage `json:"result"`
+	Error  string          `json:"error"`
+}
+
+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 input.Error != "" {
+		out, _ := json.Marshal(map[string]interface{}{
+			"success": true,
+			"data": map[string]interface{}{
+				"branch": "catch",
+				"error":  input.Error,
+			},
+		})
+		os.Stdout.Write(out)
+		return
+	}
+
+	out, _ := json.Marshal(map[string]interface{}{
+		"success": true,
+		"data": map[string]interface{}{
+			"branch": "try",
+			"result": input.Result,
+		},
+	})
+	os.Stdout.Write(out)
+}
+
+func writeError(msg string) {
+	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
+	os.Stdout.Write(out)
+}