diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a4..d36851c 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,8 @@
 **Vulnerability:** Unvalidated inputs passed to `if()` statements can cause process crashes (`condition has length > 1`) or unexpected coercion vulnerabilities.
 **Learning:** In R, optional boolean parameters that default to `NULL` should be validated using explicit runtime type validation (e.g., `if (!is.null(flag) && (!is.logical(flag) || length(flag) != 1 || is.na(flag)))`).
 **Prevention:** Always implement explicit runtime type validation for optional boolean parameters.
+
+## 2026-08-13 - Bound interactive binary choices before integer coercion
+**Vulnerability:** A menu prompt accepted any digit string with `^[0-9]+$`; an out-of-range integer could coerce to `NA_integer_` and abort later condition evaluation.
+**Learning:** Validate menu input against the documented value set before coercion.
+**Prevention:** Use an exact bounded expression such as `^[12]$` for binary choices and retain a bounded retry limit.
diff --git a/DESCRIPTION b/DESCRIPTION
index f31d3e1..63b2ee7 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -10,7 +10,7 @@ Description: Automates fixed item parameter linking for test linking under
     the item response theory paradigm using mirt package estimates.
 License: GPL-3 | file LICENSE
 Imports: mirt, methods
-Suggests: testthat (>= 3.0.0)
+Suggests: testthat (>= 3.2.0)
 Encoding: UTF-8
 Config/testthat/edition: 3
 Config/roxygen2/version: 8.0.0
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 6254651..918e19b 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,7 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", n)) {
+        if (grepl("^[12]$", n)) {
           return(as.integer(n))
         }
       }
@@ -171,7 +171,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for oldform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
@@ -390,7 +390,7 @@ autoFIPC <-
               readline(
                 prompt = "Do you want to use default BILOG-MG priors for newform Data? (1: Yes 2: No) : "
               )
-            if (grepl("^[0-9]+$", n)) {
+            if (grepl("^[12]$", n)) {
               return(as.integer(n))
             }
           }
diff --git a/R/mock-bindings.R b/R/mock-bindings.R
new file mode 100644
index 0000000..cca365f
--- /dev/null
+++ b/R/mock-bindings.R
@@ -0,0 +1,8 @@
+# Internal namespace bindings for deterministic tests of interactive code.
+#
+# Function lookup skips these NULL values during normal execution and continues
+# to the corresponding base functions. testthat can temporarily replace the
+# pre-existing namespace bindings during R CMD check, where the namespace is
+# locked and new bindings cannot be created.
+interactive <- NULL
+readline <- NULL
diff --git a/tests/testthat/test-sentinel-input-validation.R b/tests/testthat/test-sentinel-input-validation.R
new file mode 100644
index 0000000..b06e403
--- /dev/null
+++ b/tests/testthat/test-sentinel-input-validation.R
@@ -0,0 +1,106 @@
+binary_prompt_data <- function(row_count = 40L) {
+  set.seed(20260813)
+  data.frame(
+    item_1 = stats::rbinom(row_count, 1L, 0.45),
+    item_2 = stats::rbinom(row_count, 1L, 0.55),
+    item_3 = stats::rbinom(row_count, 1L, 0.50),
+    item_4 = stats::rbinom(row_count, 1L, 0.60)
+  )
+}
+
+test_that("common-item confirmation rejects oversized integer input after three attempts", {
+  testthat::local_mocked_bindings(
+    interactive = function() TRUE,
+    readline = testthat::mock_output_sequence(
+      "999999999999999999999",
+      "999999999999999999999",
+      "999999999999999999999"
+    ),
+    .package = "aFIPC"
+  )
+
+  response_data <- binary_prompt_data()
+  expect_error(
+    suppressMessages(aFIPC::autoFIPC(
+      newformXData = response_data,
+      oldformYData = response_data,
+      newformCommonItemNames = c("item_1", "item_2"),
+      oldformCommonItemNames = c("item_1", "item_2"),
+      itemtype = "2PL"
+    )),
+    "Too many invalid common item confirmation attempts",
+    fixed = TRUE
+  )
+})
+
+test_that("old-form BILOG prompt rejects values outside the documented binary choices", {
+  testthat::local_mocked_bindings(
+    interactive = function() TRUE,
+    readline = testthat::mock_output_sequence(
+      "1",
+      "0",
+      "3",
+      "999999999999999999999"
+    ),
+    .package = "aFIPC"
+  )
+
+  response_data <- binary_prompt_data()
+  expect_error(
+    suppressMessages(aFIPC::autoFIPC(
+      newformXData = response_data,
+      oldformYData = response_data,
+      newformCommonItemNames = c("item_1", "item_2"),
+      oldformCommonItemNames = c("item_1", "item_2"),
+      itemtype = "3PL"
+    )),
+    "Too many invalid oldform BILOG prior attempts",
+    fixed = TRUE
+  )
+})
+
+test_that("new-form BILOG prompt applies the same bounded validation contract", {
+  skip_if_not_installed("mirt")
+
+  set.seed(20260814)
+  item_names <- paste0("item_", 1:4)
+  old_data <- as.data.frame(mirt::simdata(
+    a = matrix(c(0.9, 1.1, 0.8, 1.2), ncol = 1L),
+    d = c(-0.5, 0.0, 0.5, 0.8),
+    itemtype = rep("2PL", 4L),
+    N = 250L
+  ))
+  names(old_data) <- item_names
+  old_model <- mirt::mirt(
+    old_data,
+    1L,
+    itemtype = "2PL",
+    SE = FALSE,
+    verbose = FALSE,
+    technical = list(NCYCLES = 300L)
+  )
+
+  testthat::local_mocked_bindings(
+    interactive = function() TRUE,
+    readline = testthat::mock_output_sequence(
+      "1",
+      "0",
+      "3",
+      "999999999999999999999"
+    ),
+    .package = "aFIPC"
+  )
+
+  new_data <- binary_prompt_data(row_count = 250L)
+  expect_error(
+    suppressMessages(aFIPC::autoFIPC(
+      newformXData = new_data,
+      oldformYData = old_model,
+      newformCommonItemNames = c("item_1", "item_2"),
+      oldformCommonItemNames = c("item_1", "item_2"),
+      itemtype = "3PL"
+    )),
+    "Too many invalid newform BILOG prior attempts",
+    fixed = TRUE
+  )
+})