sl0ppty: bindings that need no leader

Every binding needed the prefix first, which is the safe design and the
reason a leader exists: a multiplexer that takes chords away from the
programs inside it is a multiplexer you fight. But it is the user's keyboard.
Somebody who wants ctrl+alt+arrow to move between panes should be allowed to
have it, including the part where that chord stops reaching vim.

    keys {
        direct {
            bind "ctrl+alt+left" "focus-left"
            bind "ctrl+alt+right" "focus-right"
        }
    }

A block rather than a flag on each line, because these take a chord away from
every program in every pane, and that is worth seeing at a glance -- and
worth having somewhere to write the warning down, which the config now does
in full: prefer chords no program wants, a bare letter certainly is not one,
`none` gives it back.

Three ordering decisions hold it together, none of them obvious from reading
the code, all three tested:

- the direct lookup happens *last* in the key path -- after the rename editor,
  the finder, the cheatsheet, and the prefix itself. An overlay still owns the
  keyboard, and a direct binding cannot shadow the leader, which would make
  the leader unusable with no way back. There is a test that tries exactly
  that and finds the prefix still working.
- `direct` is part of a binding's identity rather than a property of it. `x`
  after the leader and `x` on its own are two bindings; binding one must not
  silently redefine the other.
- the after-the-leader lookup falls through to direct bindings, so pressing
  the prefix first never makes a binding stop working. A rule you have to
  keep track of is a rule that will catch you out.

The cheatsheet lists them under "without the leader", apart from the rest,
because the caption at the top of it says "<prefix> then:" and these are
precisely the ones that is not true of.

The tests state the bargain rather than just the mechanism: the chord fires
with no leader, and what it fires on, the program never sees -- asserted with
`cat -v`, so a keystroke arriving in the pane is visible on screen rather
than an invisible control byte that would prove nothing either way.

1 files changed, 20 insertions, 0 deletions

diff --git a/HANDOVER.md b/HANDOVER.md
index 1950872..ea82bb5 100644
--- a/HANDOVER.md
+++ b/HANDOVER.md
@@ -235,6 +235,26 @@ repeating:
   background differs from the configured one shifts slightly. Documented next
   to `modal_scrim` rather than hidden.
 
+## Leader-less bindings
+
+`keys { direct { bind ... } }` fires without the prefix. Three ordering facts
+hold it together, and all three are tested because none is obvious from the
+code:
+
+- direct lookup happens **last** in the key path, after the rename editor, the
+  finder, the cheatsheet and the prefix itself. So an overlay still owns the
+  keyboard, and a direct binding cannot shadow the leader — which would make
+  the leader unusable with no way back.
+- `direct` is part of a binding's **identity**, not a property of it: `x`
+  after the leader and `x` on its own are two bindings, and binding one must
+  not silently redefine the other.
+- `config_lookup()` (the after-the-leader path) falls through to direct
+  bindings, so pressing the prefix first never makes a binding stop working.
+  A rule anybody has to keep track of is a rule that will surprise them.
+
+The cheatsheet lists them in their own section, because the caption at the top
+says "<prefix> then:" and these are exactly the ones that is not true of.
+
 ## Things left on the table
 
 - **A `reload` keybinding.** The config watcher made it less pressing.