fix: preserve ignored signals at shell entry

brush-core/src/traps.rs

@@ -231,12 +231,19 @@ impl TrapHandlerConfig {
     /// * `signal_type` - The type of signal to register a handler for.
     /// * `command` - The command to execute when the signal is trapped.
     /// * `source_info` - The source info for where the trap handler was defined.
+    ///
+    /// Signals recorded as ignored at shell entry remain ignored, so registration attempts for
+    /// them are silently declined.
     pub fn register_handler(
         &mut self,
         signal_type: TrapSignal,
         command: String,
         source_info: crate::SourceInfo,
     ) {
+        if self.ignored_signal_name_at_entry(signal_type).is_some() {
+            return;
+        }
+
         let _ = self.handlers.insert(
             signal_type,
             TrapHandler {
@@ -284,4 +291,44 @@ mod tests {
 
         assert_eq!(ignored, vec![(10, "SIGUSR1")]);
     }
+
+    #[test]
+    fn ignored_signal_at_entry_cannot_be_trapped_or_reset() {
+        let Some(signal) = crate::sys::signal::Signal::iterator().next() else {
+            return;
+        };
+        let trap_signal = TrapSignal::Signal(signal);
+        let mut traps = TrapHandlerConfig::default();
+        traps.record_ignored_signal_at_entry(signal as i32, signal.as_str().to_owned());
+
+        traps.register_handler(
+            trap_signal,
+            "echo caught".to_owned(),
+            crate::SourceInfo::default(),
+        );
+        traps.remove_handlers(trap_signal);
+
+        assert!(!traps.handles(trap_signal));
+        assert_eq!(
+            traps.ignored_signal_name_at_entry(trap_signal),
+            Some(signal.as_str())
+        );
+    }
+
+    #[test]
+    fn signal_not_ignored_at_entry_can_be_trapped() {
+        let Some(signal) = crate::sys::signal::Signal::iterator().next() else {
+            return;
+        };
+        let trap_signal = TrapSignal::Signal(signal);
+        let mut traps = TrapHandlerConfig::default();
+
+        traps.register_handler(
+            trap_signal,
+            "echo caught".to_owned(),
+            crate::SourceInfo::default(),
+        );
+
+        assert!(traps.handles(trap_signal));
+    }
 }

brush-shell/tests/cases/compat/builtins/trap.yaml

@@ -562,6 +562,20 @@ cases:
     stdin: |
       bash -c 'trap "" USR1; exec "$1" --norc --noprofile -c "trap -p USR1; (trap -p USR1)"' _ "$0"
 
+  - name: "signals ignored at shell entry cannot be trapped or reset"
+    stdin: |
+      bash -c 'trap "" USR1; signal=$(kill -l USR1); exec "$1" --norc --noprofile -c "$2" _ "$signal"' _ "$0" '
+        trap "echo named" USR1
+        trap -p USR1
+        trap - USR1
+        trap -p USR1
+        trap "echo numeric" "$1"
+        trap -p "$1"
+        trap - "$1"
+        trap -p "$1"
+        (trap "echo subshell" USR1; trap -p USR1)
+      '
+
   - name: "trap -p - with specific signal"
     stdin: |
       trap 'echo "[int]"' INT