diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index a8207a48..45fb7bb7 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -2,3 +2,7 @@
 **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.
+## 2024-08-26 - Fix regex validation to prevent NA coercion crashes
+**Vulnerability:** Weak regex validation (`^[0-9]+$`) allows large numeric strings to be passed to `as.integer()`, which coerces them to `NA`, causing runtime crashes (`missing value where TRUE/FALSE needed`) when evaluated in conditionals.
+**Learning:** When reading integer inputs via `readline()` in R, avoid weak regex validation like `^[0-9]+$` as large numbers coerce to `NA` via `as.integer()`.
+**Prevention:** Use strictly bounded exact-match regex like `^[12]$` for categorical numeric choices to prevent coercion crashes and DoS vulnerabilities.
diff --git a/R/aFIPC.R b/R/aFIPC.R
index 62546519..918e19b1 100644
--- a/R/aFIPC.R
+++ b/R/aFIPC.R
@@ -141,7 +141,7 @@ autoFIPC <-
       }
       for (attempt in seq_len(3)) {
         n <- readline(prompt = "Is it correct? (1: Yes 2: No) : ")
-        if (grepl("^[0-9]+$", 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))
             }
           }