coach: reopen an interrupted conversation with a visible retry

An aborted stream now leaves a trace on both ends. The unmount cleanup
records the interrupted conversation (sessionStorage, one-shot) before
the abort fires, and invalidates the cached thread + rail so the return
visit refetches the advanced server state. The /coach page consumes the
record on its next mount: a known id reopens that thread, a first-turn
abort resolves via most-recent; every explicit entry intent (?c=, ?doc=,
?workout=, ?scope=, ?ask=) wins over the resume. The persisted cancelled
marker renders as a muted interrupted note with an Ask-again action that
resubmits the question through the normal send path and its gates.
Localised in all six languages. Refs #781

messages/de.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Dokument-Chat (abgeschottet)",
         "uploadError": "Upload fehlgeschlagen. Bitte versuche es erneut.",
         "notFoundError": "Dieser Dokumentlink ist nicht mehr gültig – es wird ein normaler Chat gestartet."
+      },
+      "interrupted": {
+        "note": "Diese Antwort wurde unterbrochen, bevor sie fertig war.",
+        "retry": "Erneut fragen"
       }
     },
     "relativeJustNow": "gerade eben",

messages/en.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Fenced document chat",
         "uploadError": "Upload failed. Please try again.",
         "notFoundError": "That document link is no longer valid — starting a normal chat instead."
+      },
+      "interrupted": {
+        "note": "This answer was interrupted before it finished.",
+        "retry": "Ask again"
       }
     },
     "relativeJustNow": "just now",

messages/es.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat de documento aislado",
         "uploadError": "Error al subir. Inténtalo de nuevo.",
         "notFoundError": "Ese enlace de documento ya no es válido: se iniciará un chat normal."
+      },
+      "interrupted": {
+        "note": "Esta respuesta se interrumpió antes de terminar.",
+        "retry": "Preguntar de nuevo"
       }
     },
     "relativeJustNow": "ahora mismo",

messages/fr.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat de document cloisonné",
         "uploadError": "Échec du téléversement. Veuillez réessayer.",
         "notFoundError": "Ce lien de document n'est plus valide : une conversation normale démarre à la place."
+      },
+      "interrupted": {
+        "note": "Cette réponse a été interrompue avant la fin.",
+        "retry": "Reposer la question"
       }
     },
     "relativeJustNow": "à l’instant",

messages/it.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat documento isolata",
         "uploadError": "Caricamento non riuscito. Riprova.",
         "notFoundError": "Quel link al documento non è più valido: verrà avviata una chat normale."
+      },
+      "interrupted": {
+        "note": "Questa risposta è stata interrotta prima di essere completata.",
+        "retry": "Chiedi di nuovo"
       }
     },
     "relativeJustNow": "proprio ora",

messages/pl.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Odizolowany czat dokumentu",
         "uploadError": "Przesyłanie nie powiodło się. Spróbuj ponownie.",
         "notFoundError": "Ten link do dokumentu jest już nieprawidłowy – zamiast tego rozpoczynamy zwykły czat."
+      },
+      "interrupted": {
+        "note": "Ta odpowiedź została przerwana przed ukończeniem.",
+        "retry": "Zapytaj ponownie"
       }
     },
     "relativeJustNow": "przed chwilą",