Define mobile SSH input tiers

KEYMAP.md

@@ -38,6 +38,29 @@ The input path has three distinct layers:
 No command should inspect layout quirks directly. A new keyboard layout is a new
 source-patched profile and trace fixture, not an ad-hoc branch in command code.
 
+## Input capability tiers
+
+Mobile SSH clients commonly expose more than a plain software keyboard: Escape,
+Control, arrow keys, paste, and sometimes an attached hardware keyboard. The v1
+keymap therefore treats these as capability tiers, not separate products:
+
+1. **Core mobile tier**: commands reachable without required Esc/Ctrl/Alt,
+   function keys, number-row comfort, or symbol gymnastics. Space rails and
+   mnemonic letter aliases live here.
+2. **Mobile SSH accelerator tier**: Esc, Ctrl, arrows, Home/End/Page, and paste
+   may accelerate the same intents when the SSH client exposes them. They must
+   never be the only recovery or core editing path.
+3. **Attached keyboard tier**: Vim-style and terminal-standard direct keys such
+   as `gg`, `G`, `Ctrl-u`, `Ctrl-d`, `0`, `^`, `$`, and `.` are first-class when
+   available, but each core operation keeps a discoverable mobile fallback or
+   visible rail.
+
+When adding a binding, choose the narrowest tier that makes the operation usable,
+then document any accelerator aliases next to the canonical mobile path. If a
+terminal trace shows a client cannot send an accelerator reliably, prefer a
+source-patched layout/profile update or a visible fallback over a special-case
+command branch.
+
 ## Orthogonality rules
 
 The keymap should feel small because its parts compose: