Every keyboard open and close resized the PTY, and Claude Code's inline renderer answers each height change by clearing the screen and reprinting only the transcript tail that fits, so rows above that tail were lost from tmux for good. Measured on Claude Code 2.1.306 with tmux 3.2a: five keyboard cycles (62x38 to 62x15 and back) left 75 of 100 numbered lines in the pane's history; with the rows held the PTY stays 62x38, no SIGWINCH reaches the pane and all 100 remain (#672).
While the keyboard is up the rows captured at the show transition are held through getTerminalDimensions, columns still follow the box, and the screen, now taller than its box, is translated up by --kb-clip so the last content row sits at the bottom of the visible area. This is the one documented exception to the columns-only geometry rule: there the extra rows came from another device and nothing kept the composer in view, here they are this device's own rows held on purpose and the clip keeps the composer visible. The local-echo overlay's setRowLimit narrows the renderer's existing totalRows bound, so one place decides where a long draft stops growing downward.
Only inline renderers hold, through a new registry capability keyboardHold: 'inline' (Claude alone) published to the page as window.__codemanKeyboardHoldModes. Full-height layouts such as codex, Claude's fullscreen mode (mouse tracking on, unmeasured), and remote or docker panes resize as before. The hold is released on keyboard close, a shape change, a tab switch, a session update, a reconnect, or the setting turned off. Per-device setting Keep Size Under Keyboard, default on.
JD
3e334357e8