diff --git a/rust/.sqlx/query-0134b965d7cbf9feda5bfc93bc410d91414a44251857ba9b462c99ff88c104f3.json b/rust/.sqlx/query-0134b965d7cbf9feda5bfc93bc410d91414a44251857ba9b462c99ff88c104f3.json
new file mode 100644
index 00000000..83f3c31e
--- /dev/null
+++ b/rust/.sqlx/query-0134b965d7cbf9feda5bfc93bc410d91414a44251857ba9b462c99ff88c104f3.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "DELETE FROM signal_session_resets",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "0134b965d7cbf9feda5bfc93bc410d91414a44251857ba9b462c99ff88c104f3"
+}
diff --git a/rust/.sqlx/query-06fdf3188c162f0cc9240c17506c3f2afc80d819583d005471e2c9968dca85e2.json b/rust/.sqlx/query-06fdf3188c162f0cc9240c17506c3f2afc80d819583d005471e2c9968dca85e2.json
new file mode 100644
index 00000000..73019869
--- /dev/null
+++ b/rust/.sqlx/query-06fdf3188c162f0cc9240c17506c3f2afc80d819583d005471e2c9968dca85e2.json
@@ -0,0 +1,26 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT group_id FROM groups ORDER BY total_media_counter DESC LIMIT 1",
+  "describe": {
+    "columns": [
+      {
+        "name": "group_id",
+        "ordinal": 0,
+        "type_info": "Text",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "group_id"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "06fdf3188c162f0cc9240c17506c3f2afc80d819583d005471e2c9968dca85e2"
+}
diff --git a/rust/.sqlx/query-141c8905f5d1f47fdbd88a007115dda16edadf2e6f92e7b190e99925870bdc18.json b/rust/.sqlx/query-141c8905f5d1f47fdbd88a007115dda16edadf2e6f92e7b190e99925870bdc18.json
deleted file mode 100644
index f09b4042..00000000
--- a/rust/.sqlx/query-141c8905f5d1f47fdbd88a007115dda16edadf2e6f92e7b190e99925870bdc18.json
+++ /dev/null
@@ -1,12 +0,0 @@
-{
-  "db_name": "SQLite",
-  "query": "\n            INSERT OR REPLACE INTO receipts(receipt_id, contact_id, message, contact_will_sends_receipt, wake_receiver)\n            VALUES (?, ?, ?, ?, ?)\n            ",
-  "describe": {
-    "columns": [],
-    "parameters": {
-      "Right": 5
-    },
-    "nullable": []
-  },
-  "hash": "141c8905f5d1f47fdbd88a007115dda16edadf2e6f92e7b190e99925870bdc18"
-}
diff --git a/rust/.sqlx/query-1d5f5de6b4d541014f651aa00a2fc91cf407fef2c34a5248fca3f02dc0a4c06e.json b/rust/.sqlx/query-1d5f5de6b4d541014f651aa00a2fc91cf407fef2c34a5248fca3f02dc0a4c06e.json
new file mode 100644
index 00000000..48b0a6a3
--- /dev/null
+++ b/rust/.sqlx/query-1d5f5de6b4d541014f651aa00a2fc91cf407fef2c34a5248fca3f02dc0a4c06e.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "\n                INSERT INTO signal_identities(name, identity_key, timestamp)\n                VALUES('restored-peer', x'040506', 1)\n                ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "1d5f5de6b4d541014f651aa00a2fc91cf407fef2c34a5248fca3f02dc0a4c06e"
+}
diff --git a/rust/.sqlx/query-34ad29e5771ec73110b509a063ff69e5f4b349c2efab46a250a1952ea4e7ade5.json b/rust/.sqlx/query-34ad29e5771ec73110b509a063ff69e5f4b349c2efab46a250a1952ea4e7ade5.json
new file mode 100644
index 00000000..c38b7602
--- /dev/null
+++ b/rust/.sqlx/query-34ad29e5771ec73110b509a063ff69e5f4b349c2efab46a250a1952ea4e7ade5.json
@@ -0,0 +1,21 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT COUNT(*) AS \"count!: i64\" FROM signal_sessions",
+  "describe": {
+    "columns": [
+      {
+        "name": "count!: i64",
+        "ordinal": 0,
+        "type_info": "Integer",
+        "origin": "Expression"
+      }
+    ],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "34ad29e5771ec73110b509a063ff69e5f4b349c2efab46a250a1952ea4e7ade5"
+}
diff --git a/rust/.sqlx/query-36b3701a17e020cc774c15ea84267e5f99d53ac3aca4adb323697cb87e683b1f.json b/rust/.sqlx/query-36b3701a17e020cc774c15ea84267e5f99d53ac3aca4adb323697cb87e683b1f.json
new file mode 100644
index 00000000..d37b0e75
--- /dev/null
+++ b/rust/.sqlx/query-36b3701a17e020cc774c15ea84267e5f99d53ac3aca4adb323697cb87e683b1f.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "\n            INSERT INTO receipts(receipt_id, contact_id, message, contact_will_sends_receipt, wake_receiver)\n            VALUES (?, ?, ?, ?, ?)\n            ON CONFLICT(receipt_id) DO NOTHING\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 5
+    },
+    "nullable": []
+  },
+  "hash": "36b3701a17e020cc774c15ea84267e5f99d53ac3aca4adb323697cb87e683b1f"
+}
diff --git a/rust/.sqlx/query-420d5c24bbac17a8f4db4088515782c5576ea708c9168ea2d05babd8c5a175f4.json b/rust/.sqlx/query-420d5c24bbac17a8f4db4088515782c5576ea708c9168ea2d05babd8c5a175f4.json
new file mode 100644
index 00000000..ac6d02e5
--- /dev/null
+++ b/rust/.sqlx/query-420d5c24bbac17a8f4db4088515782c5576ea708c9168ea2d05babd8c5a175f4.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "\n        INSERT INTO legacy_upgrade_requests(contact_id, requested_at)\n        VALUES (?, ?)\n        ON CONFLICT(contact_id) DO UPDATE SET requested_at = excluded.requested_at\n        WHERE legacy_upgrade_requests.requested_at <= ?\n        ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 3
+    },
+    "nullable": []
+  },
+  "hash": "420d5c24bbac17a8f4db4088515782c5576ea708c9168ea2d05babd8c5a175f4"
+}
diff --git a/rust/.sqlx/query-43583f8246016d15d9875c4d33855317c41ae07af5676228c0533724590ec6ed.json b/rust/.sqlx/query-43583f8246016d15d9875c4d33855317c41ae07af5676228c0533724590ec6ed.json
new file mode 100644
index 00000000..760cefbf
--- /dev/null
+++ b/rust/.sqlx/query-43583f8246016d15d9875c4d33855317c41ae07af5676228c0533724590ec6ed.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "DELETE FROM signal_sessions",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "43583f8246016d15d9875c4d33855317c41ae07af5676228c0533724590ec6ed"
+}
diff --git a/rust/.sqlx/query-74323299e0c048f9395ead9775a1e4b61fcc935db89378e80f30344b8c115a81.json b/rust/.sqlx/query-74323299e0c048f9395ead9775a1e4b61fcc935db89378e80f30344b8c115a81.json
new file mode 100644
index 00000000..8ce96c67
--- /dev/null
+++ b/rust/.sqlx/query-74323299e0c048f9395ead9775a1e4b61fcc935db89378e80f30344b8c115a81.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "\n                INSERT INTO signal_sessions(name, device_id, record_bytes)\n                VALUES('restored-peer', 1, x'010203')\n                ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "74323299e0c048f9395ead9775a1e4b61fcc935db89378e80f30344b8c115a81"
+}
diff --git a/rust/.sqlx/query-74e4937df433524718139d6868c4fc474939148de0f885103e7a4f39b241b553.json b/rust/.sqlx/query-74e4937df433524718139d6868c4fc474939148de0f885103e7a4f39b241b553.json
new file mode 100644
index 00000000..09067c96
--- /dev/null
+++ b/rust/.sqlx/query-74e4937df433524718139d6868c4fc474939148de0f885103e7a4f39b241b553.json
@@ -0,0 +1,26 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT identity_key FROM signal_identities WHERE name = 'restored-peer'",
+  "describe": {
+    "columns": [
+      {
+        "name": "identity_key",
+        "ordinal": 0,
+        "type_info": "Blob",
+        "origin": {
+          "Table": {
+            "table": "signal_identities",
+            "name": "identity_key"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "74e4937df433524718139d6868c4fc474939148de0f885103e7a4f39b241b553"
+}
diff --git a/rust/.sqlx/query-75f560bc922045cfacf0b5ef1f7772372cea08954859dc64de961c715ce4c55a.json b/rust/.sqlx/query-75f560bc922045cfacf0b5ef1f7772372cea08954859dc64de961c715ce4c55a.json
new file mode 100644
index 00000000..9013fb59
--- /dev/null
+++ b/rust/.sqlx/query-75f560bc922045cfacf0b5ef1f7772372cea08954859dc64de961c715ce4c55a.json
@@ -0,0 +1,21 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT COUNT(*) AS \"count!: i64\" FROM signal_session_resets",
+  "describe": {
+    "columns": [
+      {
+        "name": "count!: i64",
+        "ordinal": 0,
+        "type_info": "Integer",
+        "origin": "Expression"
+      }
+    ],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": [
+      false
+    ]
+  },
+  "hash": "75f560bc922045cfacf0b5ef1f7772372cea08954859dc64de961c715ce4c55a"
+}
diff --git a/rust/.sqlx/query-83913e710fbd04e98cd6de21e7c917ed6472ef90230a10a69f74cb07d31a99fa.json b/rust/.sqlx/query-83913e710fbd04e98cd6de21e7c917ed6472ef90230a10a69f74cb07d31a99fa.json
deleted file mode 100644
index e9f6ed5c..00000000
--- a/rust/.sqlx/query-83913e710fbd04e98cd6de21e7c917ed6472ef90230a10a69f74cb07d31a99fa.json
+++ /dev/null
@@ -1,12 +0,0 @@
-{
-  "db_name": "SQLite",
-  "query": "DELETE FROM receipts WHERE contact_id = ?",
-  "describe": {
-    "columns": [],
-    "parameters": {
-      "Right": 1
-    },
-    "nullable": []
-  },
-  "hash": "83913e710fbd04e98cd6de21e7c917ed6472ef90230a10a69f74cb07d31a99fa"
-}
diff --git a/rust/.sqlx/query-a40ea0dd25f0a1909a08aa2e1db6c5f360646a931a7e747047364a81f1e67ab5.json b/rust/.sqlx/query-a40ea0dd25f0a1909a08aa2e1db6c5f360646a931a7e747047364a81f1e67ab5.json
new file mode 100644
index 00000000..21091630
--- /dev/null
+++ b/rust/.sqlx/query-a40ea0dd25f0a1909a08aa2e1db6c5f360646a931a7e747047364a81f1e67ab5.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "UPDATE groups SET\n                   flame_counter = ?,\n                   last_flame_counter_change = ?,\n                   last_message_send = ?,\n                   last_message_received = ?\n               WHERE group_id = ?",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 5
+    },
+    "nullable": []
+  },
+  "hash": "a40ea0dd25f0a1909a08aa2e1db6c5f360646a931a7e747047364a81f1e67ab5"
+}
diff --git a/rust/.sqlx/query-b7c5107cc99685fcb27557600950b1abcb5af657b66319a01fbe7512341bdf6b.json b/rust/.sqlx/query-b7c5107cc99685fcb27557600950b1abcb5af657b66319a01fbe7512341bdf6b.json
new file mode 100644
index 00000000..9414a0a3
--- /dev/null
+++ b/rust/.sqlx/query-b7c5107cc99685fcb27557600950b1abcb5af657b66319a01fbe7512341bdf6b.json
@@ -0,0 +1,38 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT max_flame_counter, max_flame_counter_from FROM groups WHERE group_id = ?",
+  "describe": {
+    "columns": [
+      {
+        "name": "max_flame_counter",
+        "ordinal": 0,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "max_flame_counter"
+          }
+        }
+      },
+      {
+        "name": "max_flame_counter_from",
+        "ordinal": 1,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "max_flame_counter_from"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      false,
+      true
+    ]
+  },
+  "hash": "b7c5107cc99685fcb27557600950b1abcb5af657b66319a01fbe7512341bdf6b"
+}
diff --git a/rust/.sqlx/query-cb70d13126eded79712bbbfed1ae0d13c4857c1c2442be753d5ba34bf96aceb5.json b/rust/.sqlx/query-cb70d13126eded79712bbbfed1ae0d13c4857c1c2442be753d5ba34bf96aceb5.json
new file mode 100644
index 00000000..9f9db91b
--- /dev/null
+++ b/rust/.sqlx/query-cb70d13126eded79712bbbfed1ae0d13c4857c1c2442be753d5ba34bf96aceb5.json
@@ -0,0 +1,86 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT flame_counter, max_flame_counter, max_flame_counter_from,\n                      last_message_send, last_message_received, last_flame_counter_change\n               FROM groups WHERE group_id = ?",
+  "describe": {
+    "columns": [
+      {
+        "name": "flame_counter",
+        "ordinal": 0,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "flame_counter"
+          }
+        }
+      },
+      {
+        "name": "max_flame_counter",
+        "ordinal": 1,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "max_flame_counter"
+          }
+        }
+      },
+      {
+        "name": "max_flame_counter_from",
+        "ordinal": 2,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "max_flame_counter_from"
+          }
+        }
+      },
+      {
+        "name": "last_message_send",
+        "ordinal": 3,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_message_send"
+          }
+        }
+      },
+      {
+        "name": "last_message_received",
+        "ordinal": 4,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_message_received"
+          }
+        }
+      },
+      {
+        "name": "last_flame_counter_change",
+        "ordinal": 5,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_flame_counter_change"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 1
+    },
+    "nullable": [
+      false,
+      false,
+      true,
+      true,
+      true,
+      true
+    ]
+  },
+  "hash": "cb70d13126eded79712bbbfed1ae0d13c4857c1c2442be753d5ba34bf96aceb5"
+}
diff --git a/rust/.sqlx/query-db5192b62d8a4f9f23ad7befff1b9e8e463134a2cf90363a4a98d6b5b37fc723.json b/rust/.sqlx/query-db5192b62d8a4f9f23ad7befff1b9e8e463134a2cf90363a4a98d6b5b37fc723.json
new file mode 100644
index 00000000..66df7474
--- /dev/null
+++ b/rust/.sqlx/query-db5192b62d8a4f9f23ad7befff1b9e8e463134a2cf90363a4a98d6b5b37fc723.json
@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "\n                INSERT INTO signal_session_resets(\n                    name, device_id, last_reset_at, window_started_at, resets_in_window\n                ) VALUES('restored-peer', 1, 1, 1, 1)\n                ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "db5192b62d8a4f9f23ad7befff1b9e8e463134a2cf90363a4a98d6b5b37fc723"
+}
diff --git a/rust/.sqlx/query-df4c2b8e3b106c3f91e4d816627c7985c9f56fa459c16357d727fc292d226529.json b/rust/.sqlx/query-df4c2b8e3b106c3f91e4d816627c7985c9f56fa459c16357d727fc292d226529.json
new file mode 100644
index 00000000..6a5b45dd
--- /dev/null
+++ b/rust/.sqlx/query-df4c2b8e3b106c3f91e4d816627c7985c9f56fa459c16357d727fc292d226529.json
@@ -0,0 +1,86 @@
+{
+  "db_name": "SQLite",
+  "query": "SELECT group_id, flame_counter, also_best_friend,\n                      last_message_send, last_message_received, last_flame_counter_change\n               FROM groups",
+  "describe": {
+    "columns": [
+      {
+        "name": "group_id",
+        "ordinal": 0,
+        "type_info": "Text",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "group_id"
+          }
+        }
+      },
+      {
+        "name": "flame_counter",
+        "ordinal": 1,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "flame_counter"
+          }
+        }
+      },
+      {
+        "name": "also_best_friend",
+        "ordinal": 2,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "also_best_friend"
+          }
+        }
+      },
+      {
+        "name": "last_message_send",
+        "ordinal": 3,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_message_send"
+          }
+        }
+      },
+      {
+        "name": "last_message_received",
+        "ordinal": 4,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_message_received"
+          }
+        }
+      },
+      {
+        "name": "last_flame_counter_change",
+        "ordinal": 5,
+        "type_info": "Integer",
+        "origin": {
+          "Table": {
+            "table": "groups",
+            "name": "last_flame_counter_change"
+          }
+        }
+      }
+    ],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": [
+      false,
+      false,
+      false,
+      true,
+      true,
+      true
+    ]
+  },
+  "hash": "df4c2b8e3b106c3f91e4d816627c7985c9f56fa459c16357d727fc292d226529"
+}
diff --git a/rust/.sqlx/query-10facb63e1057c6acfe8b60cfe5f6deb3535eed60977d917f57cae97bb220e30.json b/rust/.sqlx/query-fef6c2ffbb80a5aa1e9cc70e3971cd9dfe0f828b984e18dff15c77389165b27c.json
similarity index 71%
rename from rust/.sqlx/query-10facb63e1057c6acfe8b60cfe5f6deb3535eed60977d917f57cae97bb220e30.json
rename to rust/.sqlx/query-fef6c2ffbb80a5aa1e9cc70e3971cd9dfe0f828b984e18dff15c77389165b27c.json
index fc127651..cb0f7f52 100644
--- a/rust/.sqlx/query-10facb63e1057c6acfe8b60cfe5f6deb3535eed60977d917f57cae97bb220e30.json
+++ b/rust/.sqlx/query-fef6c2ffbb80a5aa1e9cc70e3971cd9dfe0f828b984e18dff15c77389165b27c.json
@@ -1,6 +1,6 @@
 {
   "db_name": "SQLite",
-  "query": "SELECT group_id, total_media_counter, last_flame_counter_change,\n                      last_flame_sync, flame_counter\n               FROM groups WHERE last_flame_counter_change IS NOT NULL",
+  "query": "SELECT group_id, total_media_counter, last_flame_counter_change, last_flame_sync\n               FROM groups WHERE last_flame_counter_change IS NOT NULL",
   "describe": {
     "columns": [
       {
@@ -46,17 +46,6 @@
             "name": "last_flame_sync"
           }
         }
-      },
-      {
-        "name": "flame_counter",
-        "ordinal": 4,
-        "type_info": "Integer",
-        "origin": {
-          "Table": {
-            "table": "groups",
-            "name": "flame_counter"
-          }
-        }
       }
     ],
     "parameters": {
@@ -66,9 +55,8 @@
       false,
       false,
       true,
-      true,
-      false
+      true
     ]
   },
-  "hash": "10facb63e1057c6acfe8b60cfe5f6deb3535eed60977d917f57cae97bb220e30"
+  "hash": "fef6c2ffbb80a5aa1e9cc70e3971cd9dfe0f828b984e18dff15c77389165b27c"
 }
diff --git a/rust/src/api/messages/incoming.rs b/rust/src/api/messages/incoming.rs
index 344d16a1..a4baf703 100644
--- a/rust/src/api/messages/incoming.rs
+++ b/rust/src/api/messages/incoming.rs
@@ -297,8 +297,9 @@ async fn reset_unusable_session(
 }
 
 /// Rebuilds a v2 Signal session for a peer that still speaks the legacy
-/// protocol, so the decryption error queued for the message can be answered
-/// with a session the peer can upgrade to.
+/// protocol, so what we send them next already goes out as v2. The decryption
+/// error answering their legacy message is plaintext and does not use it; see
+/// [`claim_legacy_upgrade_request`] for how the peer itself is moved to v2.
 ///
 /// Runs before the inbound transaction opens: it awaits a server round-trip and
 /// `establish_signal_session` writes through the pool, and the app database
@@ -347,6 +348,43 @@ async fn upgrade_legacy_session_to_v2(
     Ok(())
 }
 
+/// How long a legacy peer is given to move to v2 before it is asked again.
+const LEGACY_UPGRADE_REQUEST_INTERVAL_SECS: i64 = 60 * 60;
+
+/// Claims the right to ask a legacy peer to move to v2, at most once per
+/// [`LEGACY_UPGRADE_REQUEST_INTERVAL_SECS`].
+///
+/// Clients before 0.6.0 fetch a fresh prekey bundle only for a
+/// `PREKEY_UNKNOWN` decryption error, and that bundle is what switches the
+/// contact to v2 on their side. They answer every decryption error by resending
+/// the same queued message, still encrypted as v1, so answering each of those
+/// resends would never end and would spend one of our one-time prekeys per
+/// round. Leaving the resends unanswered stops the loop: without a reply the
+/// old client does not send the message again.
+async fn claim_legacy_upgrade_request(
+    t: &mut Transaction<'_, Sqlite>,
+    contact_id: i64,
+) -> Result<bool> {
+    let now = crate::utils::current_time().timestamp();
+    let asked_before = now - LEGACY_UPGRADE_REQUEST_INTERVAL_SECS;
+    let claimed = sqlx::query!(
+        r#"
+        INSERT INTO legacy_upgrade_requests(contact_id, requested_at)
+        VALUES (?, ?)
+        ON CONFLICT(contact_id) DO UPDATE SET requested_at = excluded.requested_at
+        WHERE legacy_upgrade_requests.requested_at <= ?
+        "#,
+        contact_id,
+        now,
+        asked_before,
+    )
+    .execute(&mut **t)
+    .await?
+    .rows_affected()
+        > 0;
+    Ok(claimed)
+}
+
 #[tracing::instrument(
     skip_all,
     fields(
@@ -466,7 +504,22 @@ pub async fn handle_decoded_server_message(
             handle_sender_delivery_receipt(&mut t, from_user_id, &message.receipt_id).await?;
         }
         Type::Ciphertext | Type::PrekeyBundle => {
-            queue_decryption_error(&mut t, from_user_id, &message.receipt_id, 0).await?;
+            if claim_legacy_upgrade_request(&mut t, from_user_id).await? {
+                tracing::info!("Asking the legacy peer to fetch our v2 prekey bundle");
+                queue_decryption_error(
+                    &mut t,
+                    from_user_id,
+                    &message.receipt_id,
+                    DecryptionErrorType::PrekeyUnknown as i32,
+                )
+                .await?;
+            } else {
+                tracing::info!(
+                    "Leaving a legacy message unanswered; the peer was already asked to upgrade"
+                );
+            }
+            // Never acknowledged: the message was not read, so the sender must
+            // not be told it was delivered.
             sends_error_response = true;
         }
         Type::CiphertextV2 => {
@@ -913,4 +966,37 @@ mod tests {
             .unwrap_or_else(PoisonError::into_inner)
             .contains_key(receipt_id));
     }
+
+    /// An old client resends the same v1 message for every decryption error,
+    /// so only the first one in an interval may be answered.
+    #[tokio::test]
+    async fn a_legacy_peer_is_asked_to_upgrade_once_per_interval() {
+        let directory = tempfile::tempdir().unwrap();
+        let path = directory.path().join("app.sqlite");
+        let database = crate::database::app::AppDatabase::new(path.to_str().unwrap(), None, false)
+            .await
+            .unwrap();
+        database.run_migrations().await.unwrap();
+        sqlx::query("INSERT INTO contacts(user_id, username) VALUES (7, 'alice')")
+            .execute(&database.pool)
+            .await
+            .unwrap();
+
+        let mut t = database.pool.begin().await.unwrap();
+        assert!(claim_legacy_upgrade_request(&mut t, 7).await.unwrap());
+        assert!(!claim_legacy_upgrade_request(&mut t, 7).await.unwrap());
+        t.commit().await.unwrap();
+
+        // Once the interval has passed without the peer upgrading, it is asked
+        // again, for example because its bundle fetch failed.
+        sqlx::query("UPDATE legacy_upgrade_requests SET requested_at = requested_at - ?")
+            .bind(LEGACY_UPGRADE_REQUEST_INTERVAL_SECS)
+            .execute(&database.pool)
+            .await
+            .unwrap();
+        let mut t = database.pool.begin().await.unwrap();
+        assert!(claim_legacy_upgrade_request(&mut t, 7).await.unwrap());
+        assert!(!claim_legacy_upgrade_request(&mut t, 7).await.unwrap());
+        t.commit().await.unwrap();
+    }
 }
diff --git a/rust/src/database/app/migrations/0024_legacy_upgrade_requests.sql b/rust/src/database/app/migrations/0024_legacy_upgrade_requests.sql
new file mode 100644
index 00000000..830b319b
--- /dev/null
+++ b/rust/src/database/app/migrations/0024_legacy_upgrade_requests.sql
@@ -0,0 +1,8 @@
+-- When a peer still sending legacy (v1) Signal messages was last asked to move
+-- to v2. Older clients retry every decryption error with the same v1
+-- ciphertext, so the request is answered once per interval and the retries in
+-- between are left unanswered, which is what ends that loop.
+CREATE TABLE legacy_upgrade_requests (
+    contact_id INTEGER PRIMARY KEY REFERENCES contacts(user_id) ON DELETE CASCADE,
+    requested_at INTEGER NOT NULL
+);