diff --git a/pkg-r/R/chat.R b/pkg-r/R/chat.R
index c4afbde8..40740efd 100644
--- a/pkg-r/R/chat.R
+++ b/pkg-r/R/chat.R
@@ -113,14 +113,7 @@ commons_server <- function(id, client, ...) {
 
   prewarm_on_idle(client)
 
-  chat <- shinychat::chat_server(id, client = client, ...)
-  # shinychat owns the conversation identity (it sets the client's
-  # `conversation_id` binding, which ellmer stamps on its spans); commons
-  # only needs to know that a restore happened.
-  chat$history$on_restore(function(values) {
-    client$queue_restore_reminder()
-  })
-  chat
+  shinychat::chat_server(id, client = client, ...)
 }
 
 # An error escaping a later::later() callback would stop the app, so
diff --git a/pkg-r/R/commons.R b/pkg-r/R/commons.R
index e1634aa0..3570f60c 100644
--- a/pkg-r/R/commons.R
+++ b/pkg-r/R/commons.R
@@ -302,7 +302,13 @@ Commons <- R6::R6Class(
     },
 
     set_turns = function(value) {
-      private$restore_reminder_pending <- FALSE
+      # History that is not a prefix of the current turns may come from a
+      # previous session, where the R state behind its tool calls is gone.
+      if (length(value) == 0) {
+        private$restore_reminder_pending <- FALSE
+      } else if (!turns_are_prefix(value, self$get_turns())) {
+        private$restore_reminder_pending <- TRUE
+      }
       super$set_turns(value)
     },
 
@@ -416,11 +422,6 @@ Commons <- R6::R6Class(
       private$corpus
     },
 
-    queue_restore_reminder = function() {
-      private$restore_reminder_pending <- TRUE
-      invisible(self)
-    },
-
     prewarm = function() {
       # A direct call is typically warming caches ahead of deployment, so
       # failures propagate: a cold cache should fail the deploy.
diff --git a/pkg-r/R/turn-reminder.R b/pkg-r/R/turn-reminder.R
index 334aa6b9..9b611665 100644
--- a/pkg-r/R/turn-reminder.R
+++ b/pkg-r/R/turn-reminder.R
@@ -35,3 +35,26 @@ append_restored_conversation_reminder <- function(inputs) {
     list(ContentTurnReminder(text = restored_conversation_turn_reminder))
   )
 }
+
+# shinychat reconstructs stored turns, so compare their roles and text rather
+# than the resulting objects.
+turns_are_prefix <- function(value, current) {
+  if (length(value) > length(current)) {
+    return(FALSE)
+  }
+  identical(
+    vapply(value, turn_text_signature, character(1)),
+    vapply(current[seq_along(value)], turn_text_signature, character(1))
+  )
+}
+
+turn_text_signature <- function(turn) {
+  texts <- vapply(
+    turn@contents,
+    function(content) {
+      if (S7::S7_inherits(content, ellmer::ContentText)) content@text else ""
+    },
+    character(1)
+  )
+  paste(c(turn@role, texts), collapse = "\x1f")
+}
diff --git a/pkg-r/tests/testthat/test-chat.R b/pkg-r/tests/testthat/test-chat.R
index 359307b2..f1f3043c 100644
--- a/pkg-r/tests/testthat/test-chat.R
+++ b/pkg-r/tests/testthat/test-chat.R
@@ -43,33 +43,6 @@ test_that("commons_server runs under shiny::testServer without error", {
   succeed()
 })
 
-test_that("commons_server queues a restore reminder when history is restored", {
-  skip_if_not_installed("shiny")
-  skip_if_not_installed("shinychat")
-
-  shiny::testServer(
-    function(input, output, session) {
-      agent <- test_agent()
-      chat <- commons_server("chat", client = agent)
-    },
-    {
-      controller <- shinychat:::get_session_chat_bookmark_info(
-        session,
-        "chat.history-controller"
-      )
-      controller$restore_app_state(list())
-      expect_true(agent$.__enclos_env__$private$restore_reminder_pending)
-
-      chat$clear()
-      expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
-
-      controller$restore_app_state(list())
-      controller$new_chat()
-      expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
-    }
-  )
-})
-
 test_that("commons_theme() bundles the commons chat assets", {
   theme <- commons_theme()
 
diff --git a/pkg-r/tests/testthat/test-commons.R b/pkg-r/tests/testthat/test-commons.R
index fb68592a..a2915413 100644
--- a/pkg-r/tests/testthat/test-commons.R
+++ b/pkg-r/tests/testthat/test-commons.R
@@ -662,9 +662,20 @@ test_that("Claude 5 user turns contain one hidden reminder", {
   )
 })
 
+foreign_turns <- function() {
+  list(
+    ellmer::UserTurn("An earlier question."),
+    ellmer::AssistantTurn(
+      list(ellmer::ContentText("An earlier answer.")),
+      tokens = c(0, 0, 0),
+      cost = 0
+    )
+  )
+}
+
 test_that("restored conversations add one hidden reminder to the next turn", {
   agent <- test_agent()
-  agent$queue_restore_reminder()
+  agent$set_turns(foreign_turns())
 
   unused_stream <- agent$stream_async("Do not consume this stream.")
   expect_s3_class(unused_stream, "coro_generator_instance")
@@ -700,13 +711,35 @@ test_that("restored conversations add one hidden reminder to the next turn", {
 
 test_that("replacing restored history clears its queued reminder", {
   agent <- test_agent()
-  agent$queue_restore_reminder()
+  agent$set_turns(foreign_turns())
+  expect_true(agent$.__enclos_env__$private$restore_reminder_pending)
 
   agent$set_turns(list())
 
   expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
 })
 
+test_that("set_turns queues the restore reminder for foreign history only", {
+  agent <- test_agent()
+  stream_citations_fixture(agent, "First answer.", split_at = 5)
+  turns <- agent$get_turns()
+
+  agent$set_turns(turns[1])
+  expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
+
+  agent$set_turns(turns[1])
+  expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
+
+  agent$set_turns(foreign_turns())
+  expect_true(agent$.__enclos_env__$private$restore_reminder_pending)
+
+  agent$set_turns(foreign_turns())
+  expect_true(agent$.__enclos_env__$private$restore_reminder_pending)
+
+  agent$set_turns(list())
+  expect_false(agent$.__enclos_env__$private$restore_reminder_pending)
+})
+
 test_that("stream_async projects citations without touching stored turns", {
   path <- withr::local_tempfile(fileext = ".md")
   writeLines("Canopy cover is always acre-weighted for reporting.", path)