Harry Bayliss
58dbb56937
Codex (Ratatui) emits an 8x RI burst on startup right after setting DECSTBM. RI at the top of the scroll region scrolls the region down, and DECSTBM only constrains rows -- so the scroll spans every column and drags the right-rail session-tree entries down with the main pane. The chrome cache then hid the clobber because the computed sidebar frame was unchanged. The viewport renderer now flags any chunk containing RI / IND / NEL / SU / SD / IL / DL and OnPTYOut drops the sidebar cache when the flag is set, so the next drawSidebar repaints over the drift. Adds unit tests for the new flag and a harness regression scenario (sidebar_survives_ri_scroll) that fails without the fix.