The desktop app's chat panel reuses tui_gateway as its backend, so every chat session was stamped platform="tui". That made the agent read terminal-specific platform guidance while running in the graphical desktop chat surface.
Resolve the misclassification at its source: tui_gateway now picks platform="desktop" when HERMES_DESKTOP=1 and HERMES_DESKTOP_TERMINAL is unset, and keeps platform="tui" for the embedded terminal pane and standalone TUI. Add a PLATFORM_HINTS["desktop"] entry describing the actual chat surface (full GFM markdown, MEDIA: intercept, inline images). Move the embedded-pane clarifier to the platform-hint resolution site so it appends only to the tui hint under HERMES_DESKTOP_TERMINAL=1. Delete the now-dead desktop-hint block from build_environment_hints() that competed with the platform hint.
Standalone TUI sessions produce byte-identical prompts as before; the new desktop hint and clarifier are assembled once per session in the stable tier, so prompt caching is preserved.
