Add -P flag to read prompt from file

Implement issue 185: Create a new flag -P that reads the prompt from a
file instead of the command line.

Changes:
- Add -P flag parsing in main.cpp
- Read prompt content from specified file
- Update help message
- Update README.md documentation
- Add test_prompt_file.sh with tests for basic, multi-line, and error cases

README.md

@@ -75,6 +75,7 @@ configuration.
 *   `-s <name>`: Manually constrain the harness to a specific subset of skills (can be specified multiple times)
 *   `-i <path>`: Image file to attach to the prompt (can be specified multiple times)
 *   `-m <prompt>`: The user prompt to send to the agent.
+*   `-P <file>`: Read the prompt from a file instead of the command line.
 *   `-M <model>`: Override the Ollama model (e.g., `mistral`, `llama3`).
 
 ## ✍️ Editor Integration

src/main.cpp

@@ -129,6 +129,7 @@ int main(int argc, char** argv) {
     char const* file_to_open = nullptr;
     std::string auto_temp_file;  // Path to auto-generated temp file (if any)
     char const* prompt = nullptr;
+    char const* prompt_file = nullptr;
     bool start_new = false;
     bool list_models = false;
     char const* print_file = nullptr;
@@ -166,6 +167,11 @@ int main(int argc, char** argv) {
             consume_arg();
             prompt = consume_arg();
         }
+        else if (argv[0] == std::string("-P"))
+        {
+            consume_arg();
+            prompt_file = consume_arg();
+        }
         else if (argv[0] == std::string("-M"))
         {
             consume_arg();
@@ -277,6 +283,7 @@ int main(int argc, char** argv) {
                       << "  -i <path>   Image file to attach (can be specified multiple times)\n"
                       << "  -n          Start a new conversation (auto-generates temp file if -F not specified)\n"
                       << "  -m <prompt> Prompt message (required)\n"
+                      << "  -P <file>   Read prompt from file\n"
                       << "  -M <model>  Ollama model name\n"
                       << "  -f          Open editor with full history (requires -F)\n"
                       << "  -l          List available tools\n"
@@ -539,7 +546,14 @@ int main(int argc, char** argv) {
 
     std::string final_prompt;
 
-    if (prompt) {
+    if (prompt_file) {
+        std::ifstream pf(prompt_file);
+        if (!pf.is_open()) {
+            std::cerr << "Error: Cannot open prompt file " << prompt_file << "\n";
+            return 1;
+        }
+        final_prompt = std::string((std::istreambuf_iterator<char>(pf)), std::istreambuf_iterator<char>());
+    } else if (prompt) {
         final_prompt = prompt;
     } else {
         final_prompt = expect_or_exit(run_editor(harness.serialize(), full_history));

tests/CMakeLists.txt

@@ -24,6 +24,7 @@ add_dr_test(test_tool_read_multi_modal)
 # Add feature validation tests
 add_dr_test(test_tool_restrictions)
 add_dr_test(test_n_flag)
+add_dr_test(test_prompt_file)
 add_dr_test(test_load_chat)
 add_dr_test(process_reasoning)
 add_dr_test(test_skill_scanner)

tests/test_prompt_file.sh

@@ -0,0 +1,48 @@
+#!/bin/bash
+# test_prompt_file.sh - Validates the -P flag reads prompt from file
+
+# Test 1: Basic prompt file reading
+echo "This is my prompt from a file" > prompt.txt
+be_done 'Response received' | "${DRHARNESS}" -F chat.json -n -P prompt.txt -d
+
+# Verify the prompt from the file was stored in the chat history
+STORED_PROMPT=$(dr_result chat.json 0)
+if [ "${STORED_PROMPT}" != "This is my prompt from a file" ]; then
+    echo "FAIL: prompt_file - prompt not read correctly"
+    echo "Expected: 'This is my prompt from a file'"
+    echo "Got: '${STORED_PROMPT}'"
+    exit 1
+fi
+
+# Test 2: Multi-line prompt file
+cat > multiline_prompt.txt << 'PROMPT'
+Line 1
+Line 2
+Line 3
+PROMPT
+
+be_done 'Multi-line response' | "${DRHARNESS}" -F chat2.json -n -P multiline_prompt.txt -d
+
+# Verify multi-line prompt was stored correctly
+STORED_PROMPT=$(dr_result chat2.json 0)
+EXPECTED_MULTILINE="Line 1
+Line 2
+Line 3"
+
+if [ "${STORED_PROMPT}" != "${EXPECTED_MULTILINE}" ]; then
+    echo "FAIL: prompt_file multiline - prompt not read correctly"
+    echo "Expected:"
+    echo "${EXPECTED_MULTILINE}"
+    echo "Got:"
+    echo "${STORED_PROMPT}"
+    exit 1
+fi
+
+# Test 3: Non-existent file should fail
+if "${DRHARNESS}" -F chat3.json -n -P nonexistent.txt -d < /dev/null 2>stderr_output; then
+    echo "FAIL: prompt_file nonexistent - should have failed"
+    cat stderr_output
+    exit 1
+fi
+
+echo "PASS: prompt_file"