Add unit test for ctrlc feature on shell tool (issue 193)

Test verifies that when SIGINT (Ctrl+C) is sent to drharness during
shell command execution, the tool returns the expected
'[user requested halt of program]' message.

tests/CMakeLists.txt

@@ -19,6 +19,7 @@ add_dr_test(test_tool_read_file)
 add_dr_test(test_tool_list_files)
 add_dr_test(test_tool_grep)
 add_dr_test(test_tool_shell)
+add_dr_test(test_tool_shell_ctrlc)
 add_dr_test(test_tool_read_multi_modal)
 
 # Add feature validation tests

tests/test_tool_shell_ctrlc.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# test_tool_shell_ctrlc.sh - Test ctrlc (SIGINT) handling in the shell tool
+
+# Test 1: Verify that SIGINT during shell execution results in "[user requested halt of program]" message
+tool_call run_dangerous_shell '{"command":"sleep 100","timeout_seconds":300}' >> mock_ctrlc.txt
+be_done 'Done after interrupt' >> mock_ctrlc.txt
+
+# Run drharness in background, then send SIGINT after a short delay
+"${DRHARNESS}" -F chat_ctrlc.json -n -m "Run shell with ctrlc" -t run_dangerous_shell -d < "mock_ctrlc.txt" > /dev/null 2>&1 &
+DRHARNESS_PID=$!
+
+# Wait a moment for the shell command to start
+sleep 1
+
+# Send SIGINT (Ctrl+C) to the drharness process
+kill -SIGINT $DRHARNESS_PID
+
+# Wait for drharness to complete
+wait $DRHARNESS_PID
+
+# Check that the tool result contains the ctrlc message
+TOOL_RESULT=$(dr_result chat_ctrlc.json 2)
+
+if ! echo "${TOOL_RESULT}" | grep -q "\[user requested halt of program\]"; then
+    echo "FAIL: Expected '[user requested halt of program]' in tool output"
+    echo "Got: ${TOOL_RESULT}"
+    exit 1
+fi
+
+echo "PASS: tool_shell_ctrlc"