lag-triage: timestamped, redacted flight recorder with heal-time episode snapshots

platforms/home-manager/modules/nmasur/presets/programs/zellij.nix

@@ -20,11 +20,14 @@ 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/.
+  # Flight recorder for the still-unsolved post-TUI typing lag: the lag only
+  # shows up in long-lived pane shells and has never reproduced in a fresh
+  # shell, so the recorder must already be running when it starts.
+  # Armed by `touch ~/.local/state/lag-triage/RECORD`; new panes then stream
+  # fish's debug log through flight_filter.pl, which adds millisecond
+  # timestamps (the September logs had none, which made them inconclusive)
+  # and redacts typed/pasted text. Ctrl-b (heal-autosuggest) snapshots the
+  # recent log into ~/.local/state/lag-triage/episodes/ before healing.
   # 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
@@ -32,8 +35,16 @@ let
     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)-$$.log"
+      log="$dir/flight/fish-$(date +%Y%m%d-%H%M%S)-$$.log"
+      fifo="$dir/flight/.fifo-$$"
+      rm -f "$fifo"
+      if mkfifo -m 600 "$fifo"; then
+        # The filter exits on EOF once fish (this pid after exec) exits.
+        ${lib.getExe pkgs.perl} ${./lag-triage/flight_filter.pl} "$fifo" "$log" </dev/null >/dev/null 2>&1 &
+        export FISH_DEBUG='reader,reader-render,term-support,proc-termowner,iothread,fd-monitor,topic-monitor,complete,autoload,history,uvar-notifier'
+        export FISH_DEBUG_OUTPUT="$fifo"
+        export FISH_FLIGHT_LOG="$log"
+      fi
     fi
     exec ${lib.getExe pkgs.fish} "$@"
   '';