feat(adapter): move per-source error condensing into transform_error hooks

Every upstream formats errors differently, which is adapter territory:
the protocol gains an optional transform_error(status, body) hook and all
built-in adapters implement their own envelope parsing (zen free-pool
labels, anthropic/gemini/ollama/mistral shapes, sensenova quota notes,
agentrouter WAF pages). The core keeps a single uniform fallback: when no
hook yields a reason clients get "api error <status>: unknown error" and
the raw body goes to server logs only.

internal/lua/adapters/agentrouter.lua

@@ -108,4 +108,19 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
-return adapter
+-- 错误收敛：前置 WAF 会返回整页 HTML（阿里云盾），JSON 时为 new-api 风格
+function adapter.transform_error(status, body)
+    local low = string.lower(body or "")
+    if string.sub(low, 1, 9) == "<!doctype" or string.find(low, "<html", 1, true) then
+        return "blocked by AgentRouter WAF"
+    end
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    return nil
+end
+
+return adapter

internal/lua/adapters/anthropic.lua

@@ -180,4 +180,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return ""
 end
 
+-- 错误收敛：Anthropic 信封 {type:"error", error:{type, message}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    if resp.type == "error" and type(resp.error) == "table"
+        and type(resp.error.message) == "string" then
+        return resp.error.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/deepseek.lua

@@ -127,4 +127,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：DeepSeek 走标准 OpenAI 信封 {error:{message,...}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/gemini.lua

@@ -152,4 +152,20 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：Gemini REST 信封 {error:{code, message, status}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" then
+        if type(e.message) == "string" then
+            if type(e.status) == "string" then
+                return e.status .. ": " .. e.message
+            end
+            return e.message
+        end
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/github.lua

@@ -108,4 +108,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：GitHub Models 走标准 OpenAI 信封 {error:{message,...}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/groq.lua

@@ -107,4 +107,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：Groq 走标准 OpenAI 信封 {error:{message,...}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/kimicode.lua

@@ -140,4 +140,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
-return adapter
+-- 错误收敛：kimi 网关为 OpenAI 风格 {error:{message,...}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    return nil
+end
+
+return adapter

internal/lua/adapters/mistral.lua

@@ -107,4 +107,14 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：Mistral 用顶层 {message="...", type="..."}（非嵌套 error）
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    if type(resp.message) == "string" then
+        return resp.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/ollama.lua

@@ -131,4 +131,15 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：Ollama 常见 {error:"..."} 字符串（新版本也有对象形态）
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    if type(resp.error) == "string" then return resp.error end
+    if type(resp.error) == "table" and type(resp.error.message) == "string" then
+        return resp.error.message
+    end
+    return nil
+end
+
 return adapter

internal/lua/adapters/openai.lua

@@ -111,4 +111,16 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：标准 OpenAI 信封 {error:{message,...}}
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) == "table" and type(e.message) == "string" then
+        return e.message
+    end
+    if type(e) == "string" then return e end
+    return nil
+end
+
 return adapter

internal/lua/adapters/opencode.lua

@@ -183,4 +183,17 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛（可选钩子）：zen 错误信封固定为 {error={type,message}}；
+-- 免费池限流 FreeUsageLimitError 单独标注。返回 nil 走通用兜底。
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) ~= "table" then return nil end
+    if e.type == "FreeUsageLimitError" then
+        return "zen free pool quota exhausted"
+    end
+    return e.message
+end
+
 return adapter

internal/lua/adapters/sensenova.lua

@@ -105,4 +105,19 @@ function adapter.transform_stream_chunk(raw_chunk)
     return json.encode(unified)
 end
 
+-- 错误收敛：sensenova 为 OpenAI 风格 {error:{message,...}}；
+-- 配额类错误单独点出便于客户端识别重置周期。
+function adapter.transform_error(status, body)
+    local ok, resp = pcall(json.decode, body)
+    if not ok or type(resp) ~= "table" then return nil end
+    local e = resp.error
+    if type(e) ~= "table" then return nil end
+    if status == 429 and type(e.code) == "string"
+        and e.code == "insufficient_quota" then
+        return "workspace quota exhausted (resets periodically)"
+    end
+    if type(e.message) == "string" then return e.message end
+    return nil
+end
+
 return adapter

internal/lua/vm.go

@@ -407,6 +407,46 @@ func (v *VM) BuildHeaders(name string, meta map[string]interface{}) (map[string]
 	return headers, nil
 }
 
+// TransformError executes the optional adapter.transform_error(status, body)
+// hook: per-source condensing of an upstream error response into a short
+// client-facing reason. ok=false means the adapter defines no hook (or it
+// failed) — the caller falls back to the generic Go-side condenser.
+func (v *VM) TransformError(name string, status int, body string) (reason string, ok bool, err error) {
+	p := v.pool(name)
+	if p == nil {
+		return "", false, fmt.Errorf("adapter %s not loaded", name)
+	}
+	w, err := p.acquire()
+	if err != nil {
+		return "", false, err
+	}
+	defer p.release(w)
+	L := w.L
+
+	L.SetTop(0)
+	defer L.SetTop(0)
+	L.GetGlobal(adapterGlobal)
+	if L.IsNil(-1) {
+		return "", false, nil
+	}
+	L.GetField(-1, "transform_error")
+	if !L.IsFunction(-1) {
+		return "", false, nil
+	}
+	L.SetTop(0)
+	L.GetGlobal(adapterGlobal)
+	L.GetField(-1, "transform_error")
+	L.PushInteger(int64(status))
+	L.PushString(body)
+	if callErr := L.Call(2, 1); callErr != nil {
+		return "", false, fmt.Errorf("transform_error: %w", callErr)
+	}
+	if L.Type(-1) != golua.LUA_TSTRING {
+		return "", false, nil
+	}
+	return L.ToString(-1), true, nil
+}
+
 func (v *VM) Endpoint(name string) string {
 	p := v.pool(name)
 	if p == nil {