fix(cliproxy): centralize client error status mapping and apply context cancellation/deadline HTTP codes

Closes: #4601

internal/clienterror/client_error.go

@@ -2,6 +2,7 @@
 package clienterror
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"net/http"
@@ -10,6 +11,10 @@ import (
 	"github.com/tidwall/gjson"
 )
 
+// StatusClientClosedRequest is the nginx-style status used when the client
+// aborts the request before the proxy finishes (context.Canceled).
+const StatusClientClosedRequest = 499
+
 var requestFaultCodes = map[string]struct{}{
 	"cyber_policy":                {},
 	"context_length_exceeded":     {},
@@ -29,6 +34,40 @@ var requestFaultTypes = map[string]struct{}{
 	"invalid_prompt":        {},
 }
 
+// HTTPStatusFromError extracts an HTTP status from err.
+// Explicit StatusCode() values win. Otherwise context.Canceled maps to 499
+// and context.DeadlineExceeded maps to 504. Returns 0 when unknown.
+func HTTPStatusFromError(err error) int {
+	if err == nil {
+		return 0
+	}
+	type statusCoder interface {
+		StatusCode() int
+	}
+	var sc statusCoder
+	if errors.As(err, &sc) && sc != nil {
+		if code := sc.StatusCode(); code > 0 {
+			return code
+		}
+	}
+	if errors.Is(err, context.Canceled) {
+		return StatusClientClosedRequest
+	}
+	if errors.Is(err, context.DeadlineExceeded) {
+		return http.StatusGatewayTimeout
+	}
+	return 0
+}
+
+// HTTPStatusFromErrorOr is like HTTPStatusFromError but returns fallback when
+// the error does not carry a known status.
+func HTTPStatusFromErrorOr(err error, fallback int) int {
+	if code := HTTPStatusFromError(err); code > 0 {
+		return code
+	}
+	return fallback
+}
+
 // IsRequestFault reports whether an upstream failure is caused by the request
 // and therefore must not rotate or penalize credentials.
 func IsRequestFault(status int, err error) bool {