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.

platforms/home-manager/modules/nmasur/presets/programs/lag-triage/lag-sample.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"