web: fix red-team breaks in restore, drop-open, and plot paths

Three attack agents (state-machine tracing, executable input fuzzing,
browser-API review) found two breaks and several degradations; all are
fixed here, with the fuzzer's 22 tests kept as regression suites.

Breaks:
- Untitled tabs (and dot-names like ".dxf") autosave as DXF, but the
  restore name defaulted to .dwg — the worker dispatches its reader by
  the name's extension, so the only copy of unsaved work could never
  be restored and was re-offered forever. recovered_name now uses the
  worker's rsplit('.') convention and defaults extensionless names to
  dxf, matching new-document serialization.
- " (recovered)" stacked one suffix per crash-restore cycle; the
  marker is now stripped idempotently before appending.
- Opening a file (Ctrl+O / OPEN / automation) while a web open was in
  flight clobbered it: the in-flight open's bytes were lost and every
  queued restore prompt stalled for the session. on_open_file now
  refuses while an open is running (web only).

Hardening:
- Escape on the Recover Drawing modal defers instead of deleting the
  only snapshot; the Discard button still removes it.
- A cap-rejected restore enqueue warns in-app and re-offers the next
  snapshot; the drop queue cap rises to 32.
- Exiting mid-round no longer races snapshot removals (deferrals are
  drained, the sweep skips while a round is in flight); closing a tab
  with "Don't save" now also removes its web snapshot; the snapshot
  key derivation is shared via web_autosave_key.
- The plot-preview overlay no longer leaks a full PDF copy per preview
  (the Download closure lives in a replaceable registry).
- A corrupt autosave index.json fails the round/boot instead of
  silently resetting every row; plot pages with non-finite or non-
  positive sheet dimensions error instead of emitting a NaN MediaBox.
- The drop filter accepts dot-less "DWG"/"dxf" names the worker
  parses (same rsplit convention on both gates).

(cherry picked from commit 3eab00bfbf)

Ported onto main (#1717 review): the five standalone tests/*_redteam.rs
files stay out — no test target builds them and they exercised copies of
the functions rather than the code itself.

locales/ar-SA/opencadstudio.ftl

@@ -290,6 +290,8 @@ common =
     .autosave-copy-could-not-be-stored = تعذر تخزين نسخة الحفظ التلقائي: __ocs_fmt_0__
     .restored-from-the-autosave-copy = تم استرداد "__ocs_fmt_0__" من نسخة الحفظ التلقائي
     .autosave-copy-could-not-be-read = تعذر قراءة نسخة الحفظ التلقائي: __ocs_fmt_0__
+    .an-open-is-already-in-progress = هناك عملية فتح جارية بالفعل.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = تعذر وضع نسخة الحفظ التلقائي في قائمة الانتظار: عدد عمليات الفتح المعلقة كبير جدًا
     .jogged-radius = نصف قطر منكسر
     .none-use-shortcuts-set-key-command =   (لا شيء — استخدم: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   المحاذاة:

locales/bg-BG/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Копието от автоматичното записване не можа да бъде съхранено: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" беше възстановен от копието от автоматичното записване
     .autosave-copy-could-not-be-read = Копието от автоматичното записване не можа да бъде прочетено: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Вече се отваря файл.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Копието от автоматичното записване не можа да бъде поставено на опашка: твърде много чакащи отваряния
     .jogged-radius = Радиус с чупка
     .none-use-shortcuts-set-key-command =   (няма — използвай: SHORTCUTS SET <клавиш> <команда>)
     .alignment-indented-label-title-case =   Подравняване:

locales/cs-CZ/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Kopii automatického uložení nelze uložit: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" byl obnoven z kopie automatického uložení
     .autosave-copy-could-not-be-read = Kopii automatického uložení nelze přečíst: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Otevírání souboru již probíhá.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Kopii automatického uložení nelze zařadit do fronty: příliš mnoho čekajících otevření
     .jogged-radius = Zalomený poloměr
     .none-use-shortcuts-set-key-command =(žádné — použijte: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   Zarovnání:

locales/de-DE/opencadstudio.ftl

@@ -278,6 +278,8 @@ common =
     .autosave-copy-could-not-be-stored = Automatische Sicherungskopie konnte nicht gespeichert werden: __ocs_fmt_0__
     .restored-from-the-autosave-copy = „__ocs_fmt_0__“ wurde aus der automatischen Sicherungskopie wiederhergestellt
     .autosave-copy-could-not-be-read = Automatische Sicherungskopie konnte nicht gelesen werden: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Es wird bereits eine Datei geöffnet.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Automatische Sicherungskopie konnte nicht in die Warteschlange gestellt werden: zu viele ausstehende Öffnungsvorgänge
     .jogged-radius = Geknickter Radius
     .none-use-shortcuts-set-key-command = (keine — verwenden: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case = Ausrichtung:

locales/el-GR/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Δεν ήταν δυνατή η αποθήκευση του αντιγράφου αυτόματης αποθήκευσης: __ocs_fmt_0__
     .restored-from-the-autosave-copy = Το "__ocs_fmt_0__" επαναφέρθηκε από το αντίγραφο αυτόματης αποθήκευσης
     .autosave-copy-could-not-be-read = Δεν ήταν δυνατή η ανάγνωση του αντιγράφου αυτόματης αποθήκευσης: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Μια διαδικασία ανοίγματος βρίσκεται ήδη σε εξέλιξη.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Το αντίγραφο αυτόματης αποθήκευσης δεν μπόρεσε να μπει στην ουρά: υπερβολικά πολλές εκκρεμείς ανοίξεις
     .revolve-created-objects-failed-sources = REVOLVE: δημιουργήθηκαν __ocs_arg_created__ αντικείμενα· __ocs_arg_failed__ αρχικά αντικείμενα δεν μπόρεσαν να περιστραφούν.
     .revolve-no-selected-object-could-be-revolved = REVOLVE: κανένα επιλεγμένο αντικείμενο δεν μπόρεσε να περιστραφεί με τις ζητούμενες επιλογές.
     .none-use-shortcuts-set-key-command = (κανένα — χρησιμοποιήστε: SHORTCUTS SET <πλήκτρο> <εντολή>)

locales/en-US/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Autosave copy could not be stored: __ocs_fmt_0__
     .restored-from-the-autosave-copy = Restored "__ocs_fmt_0__" from the autosave copy
     .autosave-copy-could-not-be-read = Autosave copy could not be read: __ocs_fmt_0__
+    .an-open-is-already-in-progress = An open is already in progress.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Autosave copy could not be queued: too many pending opens
     .none-use-shortcuts-set-key-command =   (none — use: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   Alignment:
     .background-fill-enabled =   Background fill enabled

locales/es-ES/opencadstudio.ftl

@@ -278,6 +278,8 @@ common =
     .autosave-copy-could-not-be-stored = No se pudo guardar la copia de autoguardado: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" restaurado desde la copia de autoguardado
     .autosave-copy-could-not-be-read = No se pudo leer la copia de autoguardado: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Ya hay una apertura en curso.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = No se pudo poner en cola la copia de autoguardado: demasiadas aperturas pendientes
     .jogged-radius = Radio con recodo
     .none-use-shortcuts-set-key-command =   (ninguno — use: SHORTCUTS SET <tecla> <comando>)
     .alignment-indented-label-title-case =   Alineación:

locales/fi-FI/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Automaattisen tallennuksen kopiota ei voitu tallentaa: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" palautettiin automaattisen tallennuksen kopiosta
     .autosave-copy-could-not-be-read = Automaattisen tallennuksen kopiota ei voitu lukea: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Tiedoston avaaminen on jo käynnissä.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Automaattisen tallennuksen kopiota ei voitu jonottaa: liikaa odottavia avauksia
     .jogged-radius = Katkaistu säde
     .none-use-shortcuts-set-key-command =(ei mitään — käytä: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   Tasaus:

locales/fr-FR/opencadstudio.ftl

@@ -278,6 +278,8 @@ common =
     .autosave-copy-could-not-be-stored = Impossible de stocker la copie de sauvegarde automatique : __ocs_fmt_0__
     .restored-from-the-autosave-copy = «__ocs_fmt_0__» restauré depuis la copie de sauvegarde automatique
     .autosave-copy-could-not-be-read = Impossible de lire la copie de sauvegarde automatique : __ocs_fmt_0__
+    .an-open-is-already-in-progress = Une ouverture est déjà en cours.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Impossible de mettre la copie de sauvegarde automatique en file d'attente : trop d'ouvertures en attente
     .jogged-radius = Rayon raccourci
     .none-use-shortcuts-set-key-command = (aucune utilisation: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case = Alignement :

locales/hi-IN/opencadstudio.ftl

@@ -266,6 +266,8 @@ common =
     .autosave-copy-could-not-be-stored = ऑटोसेव प्रतिलिपि संग्रहित नहीं की जा सकी: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" को ऑटोसेव प्रतिलिपि से पुनर्स्थापित किया गया
     .autosave-copy-could-not-be-read = ऑटोसेव प्रतिलिपि पढ़ी नहीं जा सकी: __ocs_fmt_0__
+    .an-open-is-already-in-progress = एक फ़ाइल पहले से ही खोली जा रही है।
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = ऑटोसेव प्रतिलिपि कतार में नहीं रखी जा सकी: बहुत अधिक लंबित खोलने की क्रियाएँ
     .jogged-radius = मोड़ वाला त्रिज्या माप
     .none-use-shortcuts-set-key-command = (कोई नहीं — उपयोग: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case = संरेखण:

locales/hu-HU/opencadstudio.ftl

@@ -289,6 +289,20 @@ common =
     .autosave-copy-could-not-be-stored = Az automatikus mentési másolatot nem sikerült tárolni: __ocs_fmt_0__
     .restored-from-the-autosave-copy = A(z) "__ocs_fmt_0__" helyreállítva az automatikus mentési másolatból
     .autosave-copy-could-not-be-read = Az automatikus mentési másolatot nem sikerült elolvasni: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Már folyamatban van egy megnyitás.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Az automatikus mentési másolatot nem sikerült sorba állítani: túl sok függőben lévő megnyitás
+    .jogged-radius = Tört sugarú méret
+    .none-use-shortcuts-set-key-command =(nincs – használat: SHORTCUTS SET <key> <command>)
+    .alignment-indented-label-title-case =   Igazítás:
+    .background-fill-enabled =   Háttérkitöltés engedélyezve
+    .borders-type-weight-color-spacing-hidden =   Szegélyek (típus / súly / szín / térköz / rejtett)
+    .data-type =   Adattípus:
+    .fill-color-indented-label-sentence-case =   Kitöltés színe:
+    .format-string =   Karakterlánc formázása:
+    .off-color-ltype =   Ki Szín Ltípus
+    .text-color-indented-label-sentence-case =   Szöveg színe:
+    .text-height-indented-label-sentence-case =   Szöveg magassága:
+    .unit-type =   Egység típusa:
     .name-already-in-use = A „__ocs_fmt_0__” név már használatban van
     .rrggbb-or-blank = #RRGGBB vagy üres
     .default-parenthesized-lowercase = (alapértelmezett)

locales/it-IT/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Impossibile salvare la copia di salvataggio automatico: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" ripristinato dalla copia di salvataggio automatico
     .autosave-copy-could-not-be-read = Impossibile leggere la copia di salvataggio automatico: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Un'apertura è già in corso.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Impossibile accodare la copia di salvataggio automatico: troppe aperture in sospeso
     .jogged-radius = Raggio spezzato
     .none-use-shortcuts-set-key-command =(nessuno — utilizzare: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   Allineamento:

locales/ja-JP/opencadstudio.ftl

@@ -268,6 +268,8 @@ common =
     .autosave-copy-could-not-be-stored = 自動保存コピーを保存できませんでした: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" を自動保存コピーから復元しました
     .autosave-copy-could-not-be-read = 自動保存コピーを読み込めませんでした: __ocs_fmt_0__
+    .an-open-is-already-in-progress = 開く操作がすでに進行中です。
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = 自動保存コピーをキューに入れられませんでした：保留中の開く操作が多すぎます
     .jogged-radius = 折れ曲がり半径
     .none-use-shortcuts-set-key-command =   （なし — SHORTCUTS SET <key> <command> を使用）
     .alignment-indented-label-title-case =   配置:

locales/ko-KR/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = 자동 저장 사본을 저장할 수 없습니다: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__"을(를) 자동 저장 사본에서 복원했습니다
     .autosave-copy-could-not-be-read = 자동 저장 사본을 읽을 수 없습니다: __ocs_fmt_0__
+    .an-open-is-already-in-progress = 열기 작업이 이미 진행 중입니다.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = 자동 저장 사본을 큐에 넣지 못했습니다: 대기 중인 열기가 너무 많습니다
     .jogged-radius = 꺾인 반지름
     .none-use-shortcuts-set-key-command =   (없음 — 사용: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =정렬:

locales/nl-NL/opencadstudio.ftl

@@ -278,6 +278,8 @@ common =
     .autosave-copy-could-not-be-stored = Automatische opslagkopie kon niet worden bewaard: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" is hersteld uit de automatische opslagkopie
     .autosave-copy-could-not-be-read = Automatische opslagkopie kon niet worden gelezen: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Er wordt al een bestand geopend.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Automatische opslagkopie kon niet in de wachtrij worden geplaatst: te veel wachtende openingen
     .jogged-radius = Geknikte straal
     .none-use-shortcuts-set-key-command = (geen gebruik: SHORTCUTS SET <toets> <opdracht>)
     .alignment-indented-label-title-case = Uitlijning:

locales/pl-PL/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = Nie można zapisać kopii autozapisu: __ocs_fmt_0__
     .restored-from-the-autosave-copy = Przywrócono "__ocs_fmt_0__" z kopii autozapisu
     .autosave-copy-could-not-be-read = Nie można odczytać kopii autozapisu: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Otwieranie jest już w toku.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Nie można ustawić kopii autozapisu w kolejce: zbyt wiele oczekujących otwarć
     .jogged-radius = Promień łamany
     .none-use-shortcuts-set-key-command =(brak — użyj: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case =   Wyrównanie:

locales/pt-BR/opencadstudio.ftl

@@ -278,6 +278,8 @@ common =
     .autosave-copy-could-not-be-stored = Não foi possível armazenar a cópia de salvamento automático: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" restaurado da cópia de salvamento automático
     .autosave-copy-could-not-be-read = Não foi possível ler a cópia de salvamento automático: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Uma abertura já está em andamento.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Não foi possível enfileirar a cópia de salvamento automático: aberturas pendentes em excesso
     .jogged-radius = Raio com desvio
     .none-use-shortcuts-set-key-command =   (nenhum — use: SHORTCUTS SET <tecla> <comando>)
     .alignment-indented-label-title-case =   Alinhamento:

locales/ru-RU/opencadstudio.ftl

@@ -281,6 +281,8 @@ common =
     .autosave-copy-could-not-be-stored = Не удалось сохранить копию автосохранения: __ocs_fmt_0__
     .restored-from-the-autosave-copy = «__ocs_fmt_0__» восстановлен из копии автосохранения
     .autosave-copy-could-not-be-read = Не удалось прочитать копию автосохранения: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Открытие файла уже выполняется.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Не удалось поставить копию автосохранения в очередь: слишком много ожидающих открытий
     .jogged-radius = Радиус с изломом
     .none-use-shortcuts-set-key-command = (нет — используйте: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case = Выравнивание:

locales/tr-TR/opencadstudio.ftl

@@ -263,6 +263,8 @@ common =
     .autosave-copy-could-not-be-stored = Otomatik kayıt kopyası depolanamadı: __ocs_fmt_0__
     .restored-from-the-autosave-copy = "__ocs_fmt_0__" otomatik kayıt kopyasından geri yüklendi
     .autosave-copy-could-not-be-read = Otomatik kayıt kopyası okunamadı: __ocs_fmt_0__
+    .an-open-is-already-in-progress = Bir açma işlemi zaten sürüyor.
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = Otomatik kayıt kopyası sıraya alınamadı: çok fazla bekleyen açma işlemi
     .none-use-shortcuts-set-key-command = (none – use: SHORTCUTS SET <key> <command>)
     .alignment-indented-label-title-case = Adapt:
     .background-fill-enabled = Arka plan doldurma etkinleştir etkinleştirildi

locales/zh-CN/opencadstudio.ftl

@@ -265,6 +265,8 @@ common =
     .autosave-copy-could-not-be-stored = 无法存储自动保存副本: __ocs_fmt_0__
     .restored-from-the-autosave-copy = 已从自动保存副本恢复 "__ocs_fmt_0__"
     .autosave-copy-could-not-be-read = 无法读取自动保存副本: __ocs_fmt_0__
+    .an-open-is-already-in-progress = 已有打开操作正在进行。
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = 无法排队自动保存副本：待打开的文件过多
     .jogged-radius = 折弯半径
     .none-use-shortcuts-set-key-command =   （无 — 使用：SHORTCUTS SET <key> <command>）
     .alignment-indented-label-title-case = 对齐:

locales/zh-TW/opencadstudio.ftl

@@ -277,6 +277,8 @@ common =
     .autosave-copy-could-not-be-stored = 無法儲存自動儲存副本: __ocs_fmt_0__
     .restored-from-the-autosave-copy = 已從自動儲存副本恢復 "__ocs_fmt_0__"
     .autosave-copy-could-not-be-read = 無法讀取自動儲存副本: __ocs_fmt_0__
+    .an-open-is-already-in-progress = 已有開啟作業正在進行中。
+    .autosave-copy-could-not-be-queued-too-many-pending-opens = 無法將自動儲存副本排入佇列：待開啟的檔案過多
     .jogged-radius = 折彎半徑
     .none-use-shortcuts-set-key-command =   （無 — 使用：SHORTCUTS SET <key> <command>）
     .alignment-indented-label-title-case = 對齊: