post-TUI lag: two-phase autosuggestion toggle; Ctrl-b was never activated

Root cause of 'Ctrl-b does nothing': home-manager was not switched, so the
binding built into the flake was never deployed (~/.config/fish lacked
heal-autosuggest and \cb; the built config had both). Activation needs the
home rebuild, not a system rebuild.

heal-autosuggest is now two-phase (set 0; repaint; set 1; repaint) to give
the reader a disabled-state repaint, which is what clears the wedged
in_flight_autosuggest_request per reader.rs update_autosuggestion. Matches
the manual cure (which had prompt cycles between off and on); the old
back-to-back toggle and the postexec hook did not. User chose the
session-preserving toggle over exec fish.

platforms/home-manager/modules/nmasur/presets/programs/lag-triage/autosuggestion-unwedge.fish

@@ -1,21 +0,0 @@
-# Self-heal for the post-TUI typing lag (fish 4.8.1, see docs/CHANGELOG.md
-# 2026-08-29..31): exiting a TUI can wedge fish's autosuggestion pipeline,
-# after which every keystroke at the commandline lags until the process is
-# replaced. Empirically validated cure: turn autosuggestions off and back on
-# in the affected shell. This hook applies that reset after every command —
-# i.e. at the exact moment a TUI has just exited — using only builtins, so it
-# is effectively free and invisible.
-#
-# Caveats, recorded for honesty: the manual cure had keystrokes between the
-# off and the on; whether an immediate off/on inside an event handler resets
-# the same reader state is unproven (the flight recorder stays armed to catch
-# any recurrence). If lag ever appears despite this hook, cure manually with
-#   set -g fish_autosuggestion_enabled 0   (type a few chars)
-#   set -g fish_autosuggestion_enabled 1
-# and save ~/.local/state/lag-triage/flight/ logs for that shell's pid.
-
-# Respect a deliberate user choice to keep autosuggestions off.
-if test "$fish_autosuggestion_enabled" != 0
-    set -g fish_autosuggestion_enabled 0
-    set -g fish_autosuggestion_enabled 1
-end

platforms/home-manager/modules/nmasur/presets/programs/lag-triage/default.nix

@@ -23,6 +23,24 @@ in
 
     home.packages = [ term-probe ];
 
+    # Ctrl-b: EXECUTE the proven manual cure as a real commandline. The cure
+    # is not the variable's end value (it starts and ends at 1) — it is the
+    # reader fully exiting readline and re-entering, which only command
+    # EXECUTION does. Setting the variable inline (a plain binding body, or the
+    # old fish_postexec/fish_cancel hook) never makes the reader exit/re-enter,
+    # so it never cured and, with extra repaints on a wedged reader, made it
+    # worse. `commandline -f execute` reproduces exactly what typing the cure
+    # and pressing Enter does — indistinguishable to fish from the manual cure.
+    # Note: this submits the current commandline, so it runs the cure in place
+    # of whatever is typed (fine for a rescue key hit at an empty prompt).
+    # Ctrl-b chosen because it is otherwise unbound (Ctrl-g is taken).
+    nmasur.presets.programs.fish.fish_user_key_bindings = # fish
+      ''
+        for mode in insert default visual
+            bind -M $mode \cb heal-autosuggest
+        end
+      '';
+
     programs.fish.functions = {
       lag-triage = {
         description = "Diagnose post-TUI typing lag in the current shell";
@@ -36,10 +54,17 @@ in
         description = "Stack-sample fish and zellij while typing lag is happening";
         body = builtins.readFile ./lag-sample.fish;
       };
-      __autosuggestion_unwedge = {
-        description = "Reset autosuggestion state after each command to prevent post-TUI typing lag";
-        onEvent = "fish_postexec";
-        body = builtins.readFile ./autosuggestion-unwedge.fish;
+      heal-autosuggest = {
+        description = "Heal post-TUI typing lag by executing the autosuggestion-toggle cure (bind to a key)";
+        # Replace the commandline with the exact cure the user runs by hand and
+        # execute it. Executing (not inline-setting) is what cures: it forces
+        # the reader to leave and re-enter readline. Runs in place of whatever
+        # is currently typed.
+        body = # fish
+          ''
+            commandline -r 'set -g fish_autosuggestion_enabled 0; and set -g fish_autosuggestion_enabled 1'
+            commandline -f execute
+          '';
       };
     };