One request paints every open buffer, so the toggle has to ask about all of them

flan-check-memory painted every buffer visiting a file the answer named
but decided whether it was already on by looking at the current one.
Asking again from a third buffer therefore stacked a second copy on the
two that were marked, with a second help-echo, and the toggle in the
third buffer took nothing down. Both the toggle and the repaint now go
through the whole buffer list.

The comment beside the faces claimed a dotted underline. The gc face
draws a wave, the same style the error face does; what actually makes
these fainter is that neither inherits error and neither draws its
message into the line. Say that instead, in flan.el and in MANUAL.md.

emacs/MANUAL.md

@@ -562,9 +562,11 @@ this frame's memory going".
 collected heap: a string, a vec or a map crossing into `dyn`, the view record a
 typed container takes when it crosses, an `i64` too wide for a `dyn`'s payload.
 Another for an allocator the program named: a push or a `reserve` past capacity,
-a `clone`, a `slurp`, a new arena. Both are fainter than an error — a dotted or
-dimmed underline, no message drawn beside the line — because the code is not
-wrong. Hover for the sentence; the count is in the echo area.
+a `clone`, a `slurp`, a new arena. The two underlines differ in style as well as
+in colour, so you can tell the classes apart without relying on colour alone.
+Both are fainter than an error: neither inherits the error face, and neither
+draws its message into the line the way a rejection does. Hover for the
+sentence; the count is in the echo area.
 
 **What is deliberately not marked is the half worth knowing.** A `dyn` immediate
 costs nothing, so nothing is drawn: `nil`, a `bool`, an `f64`, a keyword, and any

emacs/flan.el

@@ -2731,10 +2731,12 @@ can print the same breakdown to stderr under FLAN_DEV_LEAKS."
 ;; the message to find out.
 ;;
 ;; **Fainter than an error, deliberately.**  These are annotations on code that
-;; is correct.  So: a dotted underline rather than an error's wave, a dimmed
-;; colour, and no per-site `after-string' — the message goes in `help-echo' and
-;; the count in the echo area.  An error must still win where the two land on
-;; one span, which is what the lower `priority' is for.
+;; is correct.  So: no per-site `after-string' — which is the loud half of the
+;; error overlay, a message drawn into the line — and neither face inherits
+;; `error'.  The message goes in `help-echo' and the count in the echo area.
+;; The two underlines differ in style as well as in colour, so the classes are
+;; told apart without relying on colour alone.  An error must still win where
+;; the two land on one span, which is what the lower `priority' is for.
 ;;
 ;; **And they last, which an error overlay does not.**  The error overlay is
 ;; feedback about the evaluation that just failed, so any command at all takes
@@ -2777,6 +2779,15 @@ what makes that reading stale — nothing smaller does, which is why this is
 not the `pre-command-hook' the error overlays use."
   (flan-clear-memory))
 
+(defun flan--marked-buffers ()
+  "Every buffer that currently has allocation annotations in it.
+
+One request paints every buffer visiting a file the answer names, so the
+toggle and the refresh are questions about all of them and not about the
+one point happens to be in: asking from a third buffer would otherwise
+stack a second copy on the two that were already marked."
+  (seq-filter (lambda (b) (flan--memory-overlays b)) (buffer-list)))
+
 (defun flan--memory-face (kind)
   "The face for a diagnostic of KIND, or nil if KIND is not one of ours."
   (cond ((equal kind "memory/gc") 'flan-memory-gc-face)
@@ -2825,12 +2836,17 @@ line that is marked.
 The annotations last until you edit the buffer.  Asking again while they are
 up takes them down."
   (interactive)
-  (if (flan--memory-overlays)
-      (progn (flan-clear-memory) (message "flan: allocation marks off"))
+  (if (flan--marked-buffers)
+      (progn (mapc #'flan-clear-memory (flan--marked-buffers))
+             (message "flan: allocation marks off"))
     (let ((r (flan--request (list :op "memory"))))
       (unless (equal (plist-get r :status) "ok")
         (user-error "flan: %s" (or (plist-get r :message) "refused")))
       (let ((here 0) (elsewhere 0))
+        ;; Nothing was marked in *this* buffer or the branch above would have
+        ;; run — but another one may be, and painting over it would stack a
+        ;; second copy with a second `help-echo'.
+        (mapc #'flan-clear-memory (flan--marked-buffers))
         (dolist (row (plist-get r :sites))
           (if (flan--show-memory (nth 0 row) (nth 1 row) (nth 2 row))
               (setq here (1+ here))