Frame-by-frame IMQ with an outgoing filter; HTTP interceptor hook

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/imq/frame.go

@@ -40,10 +40,11 @@ func TypeName(t uint64) string {
 	return fmt.Sprintf("type %d", t)
 }
 
-// Frame is one message: its type and the size of its data.
+// Frame is one message: its type and data (Size is len(Data)).
 type Frame struct {
 	Type uint64
 	Size int
+	Data []byte
 }
 
 // ErrMalformed means the stream isn't IMQ framing; a Reader stops decoding after it.
@@ -76,6 +77,12 @@ func (r *Reader) Write(data []byte) ([]Frame, error) {
 	}
 }
 
+// Next reads the frame at the start of b: the frame and its length in b, a length of 0 if b holds only part of it,
+// or ErrMalformed.
+func Next(b []byte) (Frame, int, error) {
+	return parse(b)
+}
+
 // maxFrame bounds a frame's size, so a stream that isn't IMQ isn't buffered without end.
 const maxFrame = 16 << 20
 
@@ -116,6 +123,7 @@ func parse(b []byte) (Frame, int, error) {
 				return f, 0, nil
 			}
 			f.Size = int(size)
+			f.Data = b[i : i+int(size) : i+int(size)]
 			return f, i + int(size), nil
 		default:
 			return f, 0, ErrMalformed