Merge remote-tracking branch 'origin/main' into pr-104

# Conflicts:
#	config.example.yaml
#	internal/config/config.go
#	sdk/cliproxy/auth/model_name_mappings.go

internal/api/modules/amp/proxy.go

@@ -3,8 +3,11 @@ package amp
 import (
 	"bytes"
 	"compress/gzip"
+	"context"
+	"errors"
 	"fmt"
 	"io"
+	"net"
 	"net/http"
 	"net/http/httputil"
 	"net/url"
@@ -102,7 +105,15 @@ func createReverseProxy(upstreamURL string, secretSource SecretSource) (*httputi
 	// Modify incoming responses to handle gzip without Content-Encoding
 	// This addresses the same issue as inline handler gzip handling, but at the proxy level
 	proxy.ModifyResponse = func(resp *http.Response) error {
-		// Only process successful responses
+		// Log upstream error responses for diagnostics (502, 503, etc.)
+		// These are NOT proxy connection errors - the upstream responded with an error status
+		if resp.StatusCode >= 500 {
+			log.Errorf("amp upstream responded with error [%d] for %s %s", resp.StatusCode, resp.Request.Method, resp.Request.URL.Path)
+		} else if resp.StatusCode >= 400 {
+			log.Warnf("amp upstream responded with client error [%d] for %s %s", resp.StatusCode, resp.Request.Method, resp.Request.URL.Path)
+		}
+
+		// Only process successful responses for gzip decompression
 		if resp.StatusCode < 200 || resp.StatusCode >= 300 {
 			return nil
 		}
@@ -186,9 +197,29 @@ func createReverseProxy(upstreamURL string, secretSource SecretSource) (*httputi
 		return nil
 	}
 
-	// Error handler for proxy failures
+	// Error handler for proxy failures with detailed error classification for diagnostics
 	proxy.ErrorHandler = func(rw http.ResponseWriter, req *http.Request, err error) {
-		log.Errorf("amp upstream proxy error for %s %s: %v", req.Method, req.URL.Path, err)
+		// Classify the error type for better diagnostics
+		var errType string
+		if errors.Is(err, context.DeadlineExceeded) {
+			errType = "timeout"
+		} else if errors.Is(err, context.Canceled) {
+			errType = "canceled"
+		} else if netErr, ok := err.(net.Error); ok && netErr.Timeout() {
+			errType = "dial_timeout"
+		} else if _, ok := err.(net.Error); ok {
+			errType = "network_error"
+		} else {
+			errType = "connection_error"
+		}
+
+		// Don't log as error for context canceled - it's usually client closing connection
+		if errors.Is(err, context.Canceled) {
+			log.Debugf("amp upstream proxy [%s]: client canceled request for %s %s", errType, req.Method, req.URL.Path)
+		} else {
+			log.Errorf("amp upstream proxy error [%s] for %s %s: %v", errType, req.Method, req.URL.Path, err)
+		}
+
 		rw.Header().Set("Content-Type", "application/json")
 		rw.WriteHeader(http.StatusBadGateway)
 		_, _ = rw.Write([]byte(`{"error":"amp_upstream_proxy_error","message":"Failed to reach Amp upstream"}`))

internal/api/modules/amp/response_rewriter.go

@@ -29,15 +29,71 @@ func NewResponseRewriter(w gin.ResponseWriter, originalModel string) *ResponseRe
 	}
 }
 
+const maxBufferedResponseBytes = 2 * 1024 * 1024 // 2MB safety cap
+
+func looksLikeSSEChunk(data []byte) bool {
+	// Fallback detection: some upstreams may omit/lie about Content-Type, causing SSE to be buffered.
+	// Heuristics are intentionally simple and cheap.
+	return bytes.Contains(data, []byte("data:")) ||
+		bytes.Contains(data, []byte("event:")) ||
+		bytes.Contains(data, []byte("message_start")) ||
+		bytes.Contains(data, []byte("message_delta")) ||
+		bytes.Contains(data, []byte("content_block_start")) ||
+		bytes.Contains(data, []byte("content_block_delta")) ||
+		bytes.Contains(data, []byte("content_block_stop")) ||
+		bytes.Contains(data, []byte("\n\n"))
+}
+
+func (rw *ResponseRewriter) enableStreaming(reason string) error {
+	if rw.isStreaming {
+		return nil
+	}
+	rw.isStreaming = true
+
+	// Flush any previously buffered data to avoid reordering or data loss.
+	if rw.body != nil && rw.body.Len() > 0 {
+		buf := rw.body.Bytes()
+		// Copy before Reset() to keep bytes stable.
+		toFlush := make([]byte, len(buf))
+		copy(toFlush, buf)
+		rw.body.Reset()
+
+		if _, err := rw.ResponseWriter.Write(rw.rewriteStreamChunk(toFlush)); err != nil {
+			return err
+		}
+		if flusher, ok := rw.ResponseWriter.(http.Flusher); ok {
+			flusher.Flush()
+		}
+	}
+
+	log.Debugf("amp response rewriter: switched to streaming (%s)", reason)
+	return nil
+}
+
 // Write intercepts response writes and buffers them for model name replacement
 func (rw *ResponseRewriter) Write(data []byte) (int, error) {
-	// Detect streaming on first write
-	if rw.body.Len() == 0 && !rw.isStreaming {
+	// Detect streaming on first write (header-based)
+	if !rw.isStreaming && rw.body.Len() == 0 {
 		contentType := rw.Header().Get("Content-Type")
 		rw.isStreaming = strings.Contains(contentType, "text/event-stream") ||
 			strings.Contains(contentType, "stream")
 	}
 
+	if !rw.isStreaming {
+		// Content-based fallback: detect SSE-like chunks even if Content-Type is missing/wrong.
+		if looksLikeSSEChunk(data) {
+			if err := rw.enableStreaming("sse heuristic"); err != nil {
+				return 0, err
+			}
+		} else if rw.body.Len()+len(data) > maxBufferedResponseBytes {
+			// Safety cap: avoid unbounded buffering on large responses.
+			log.Warnf("amp response rewriter: buffer exceeded %d bytes, switching to streaming", maxBufferedResponseBytes)
+			if err := rw.enableStreaming("buffer limit"); err != nil {
+				return 0, err
+			}
+		}
+	}
+
 	if rw.isStreaming {
 		n, err := rw.ResponseWriter.Write(rw.rewriteStreamChunk(data))
 		if err == nil {