post-TUI lag: autosuggestion culprit confirmed; add self-heal hook

A/B in a live lagging shell: disabling fish_autosuggestion_enabled cures the lag instantly, and re-enabling does NOT bring it back — the toggle resets the wedged reader state. __autosuggestion_unwedge (fish_postexec) now applies that reset after every command, at the moment TUIs exit. Builtins only, invisible, respects a deliberate manual disable. Flight recorder stays armed until the hook is proven in real use. Also from this investigation: wedged-thread evidence (sampler attach cures), lag-sample tool, flight recorder in the zellij fish wrapper.
2026-09-08 19:26:09 +00:00 · 2026-09-07 11:17:44 -04:00
parent db49e746b8
commit d4e56dd190
5 changed files with 124 additions and 1 deletions
@@ -0,0 +1,21 @@
+# 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
@@ -32,6 +32,15 @@ in
        description = "Reset terminal state left behind by a TUI";
        body = builtins.readFile ./unlag.fish;
      };
+      lag-sample = {
+        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;
+      };
    };

  };
@@ -0,0 +1,53 @@
+# Capture stack samples of this fish process, the zellij server, and the
+# zellij client WHILE the typing lag is happening. This names the guilty
+# component directly: if fish's main thread is busy/blocked per keystroke the
+# stacks show exactly where; if fish is idle while typing feels laggy, the
+# delay is in zellij's render path instead.
+#
+# CAUTION (learned 2026-08-30): attaching the sampler to a lagging fish CURES
+# the lag (thread suspend/resume unwedges it), so run this from a DIFFERENT
+# pane with the lagging shell's pid: `lag-sample <pid>` (get it in the lagging
+# shell with the builtin-only `echo $fish_pid`). Have someone type in the
+# lagging pane while sampling runs — the first samples may catch the wedge.
+# With no argument it samples the current shell.
+
+set -l target $fish_pid
+if test (count $argv) -ge 1; and test -n "$argv[1]"
+    set target $argv[1]
+end
+
+set -l outdir ~/.local/state/lag-triage
+mkdir -p $outdir
+set -l ts (date +%Y%m%d-%H%M%S)
+set -l dur 8
+
+set -l fishfile $outdir/sample-$ts-fish-$target.txt
+/usr/bin/sample $target $dur 1 -file $fishfile &>/dev/null &
+disown
+
+# this session's zellij server (socket path ends in the session name)
+set -l serverpid (pgrep -f "zellij --server.*/$ZELLIJ_SESSION_NAME\$")
+test -z "$serverpid"; and set serverpid (pgrep -f "zellij --server" | head -3)
+for pid in $serverpid
+    /usr/bin/sample $pid $dur 1 -file $outdir/sample-$ts-zellij-server-$pid.txt &>/dev/null &
+    disown
+end
+
+# zellij clients (attached to ghostty): named zellij but without --server args
+set -l allserver (pgrep -f "zellij --server")
+set -l clientpid
+for pid in (pgrep -x zellij)
+    contains $pid $allserver; or set -a clientpid $pid
+end
+for pid in $clientpid[1..3]
+    /usr/bin/sample $pid $dur 1 -file $outdir/sample-$ts-zellij-client-$pid.txt &>/dev/null &
+    disown
+end
+
+# notify when done, without occupying the commandline
+fish -c "sleep (math $dur + 2); echo; echo '== lag-sample done: '$outdir'/sample-$ts-*.txt =='" &
+disown
+
+echo "Sampling fish (pid $target), zellij server(s) [$serverpid], client(s) [$clientpid] for $dur s."
+echo ">>> TYPE CONTINUOUSLY IN THE LAGGING PANE NOW (junk text is fine) <<<"
+echo "Files: $outdir/sample-$ts-*.txt"
@@ -20,8 +20,21 @@ let
  # harness on fish 4.8.1 (see docs/CHANGELOG.md 2026-08-29 and
  # presets/programs/lag-triage/upstream_repro.py). Spawning fish with the
  # variable already exported makes every pane shell immune.
+  # Flight recorder for the still-unsolved post-TUI typing lag: sampling the
+  # process CURES the lag (a wedged thread gets kicked loose), so the only way
+  # to observe it is a recorder that is already running before the lag starts.
+  # Armed by `touch ~/.local/state/lag-triage/RECORD`; new panes then log
+  # fish's reader/thread internals to ~/.local/state/lag-triage/flight/.
+  # Remove the RECORD file to disable (zero overhead when off).
  fish-no-query-term = pkgs.writeShellScriptBin "fish-no-query-term" ''
    export fish_features=no-query-term
+    dir="$HOME/.local/state/lag-triage"
+    if [ -e "$dir/RECORD" ]; then
+      mkdir -p "$dir/flight"
+      find "$dir/flight" -type f -mtime +3 -delete 2>/dev/null
+      export FISH_DEBUG='reader,term-support,proc-termowner,iothread,fd-monitor,topic-monitor'
+      export FISH_DEBUG_OUTPUT="$dir/flight/fish-$(date +%Y%m%d-%H%M%S)-$$.log"
+    fi
    exec ${lib.getExe pkgs.fish} "$@"
  '';