feat: release configurable API response contracts

Define reusable response bodies in .api with typed code mappings, per-route overrides and matching OpenAPI schemas. Add application and callback encoders, early response policy selection, and isolated remote-consumer release verification.

Release v0.8.0-preview after full race, vet, build and local MySQL workflow acceptance.

examples/contracts/responses.api

@@ -0,0 +1,58 @@
+syntax = "v1"
+
+info (
+ title: "Configurable response example"
+ version: "1.0.0"
+)
+
+// Define the public body once. No field names are required by the framework.
+response CommonResponse (
+ body: {
+  "code": "${code}",
+  "msg": "${message}",
+  "data": "${data}"
+ }
+ codeType: int32
+ successCode: 200
+ errorCode: 9999
+ successMessage: "操作成功"
+ dataMode: always
+ codes: {"ITEM_NOT_FOUND":404001}
+ messages: {"ITEM_NOT_FOUND":"记录不存在"}
+)
+
+response PartnerResponse (
+ body: {"accepted":"${ok}","payload":"${data}","meta":{"trace":"${requestId}"}}
+ errorBody: {"accepted":"${ok}","error":{"reason":"${message}"}}
+)
+
+error ItemNotFound 404 "ITEM_NOT_FOUND" "item not found"
+
+type ItemReq {
+ ItemID int64 `path:"itemId" binding:"min=1"`
+}
+
+type ItemResp {
+ ItemID int64 `json:"itemId"`
+ Name string `json:"name"`
+}
+
+@server (
+ group: items
+ prefix: /api
+ response: CommonResponse
+)
+service response-api {
+ @errors ItemNotFound
+ @handler getItem
+ get /items/:itemId (ItemReq) returns (ItemResp)
+
+ // Success is the ItemResp object itself; errors still use CommonResponse.
+ @response raw
+ @handler rawItem
+ get /rawItems/:itemId (ItemReq) returns (ItemResp)
+
+ @response PartnerResponse
+ @handler partnerItem
+ get /partnerItems/:itemId (ItemReq) returns (ItemResp)
+}