pub const MULTIMODAL_IMAGE_MARKER: &'static str;Expand description
P4c (COMPOSABLE-HARNESS-DESIGN.md S1.2/S3.1 core.tools.read_file multimodal, S1.2 view_image): the sentinel prefix a tool’s plain
String result carries when it is actually an image data URL rather
than ordinary text — Agent::run_loop detects this prefix (before
cap_tool_output ever sees it) and builds a content_parts image
block instead of a plain-text tool result. Using a control character
(\u{1}, SOH) as part of the marker keeps a false-positive collision
with real tool output astronomically unlikely without requiring a new
Tool::execute return type across all ten built-ins (an L-sized
trait-signature change this S-sized catalog item does not call for).