feat: enhance prompt system with feature-conditional fragments and enriched tool descriptions

crates/loopal-agent-server/src/agent_setup.rs

@@ -14,12 +14,6 @@ use loopal_runtime::frontend::traits::AgentFrontend;
 
 use crate::params::StartParams;
 
-const SCHEDULER_PROMPT: &str = "\n\n# Scheduled Messages\n\
-    Messages prefixed with `[scheduled]` are injected by the cron scheduler, \
-    not typed by the user. Treat them as automated prompts and execute the \
-    requested action without asking for confirmation. \
-    Use CronCreate/CronDelete/CronList tools to manage scheduled jobs.";
-
 /// Build `AgentLoopParams` with a pre-constructed frontend (HubFrontend or IpcFrontend).
 ///
 /// The caller provides the frontend and interrupt signal, decoupling agent setup
@@ -120,6 +114,19 @@ pub fn build_with_frontend(
     let skills: Vec<_> = config.skills.values().map(|e| e.skill.clone()).collect();
     let skills_summary = loopal_config::format_skills_summary(&skills);
     let tool_defs = kernel.tool_definitions();
+
+    let mut features = Vec::new();
+    if config.settings.memory.enabled && memory_channel.is_some() {
+        features.push("memory".into());
+    }
+    if !config.settings.hooks.is_empty() {
+        features.push("hooks".into());
+    }
+    features.push("subagent".into());
+    if !config.settings.output_style.is_empty() {
+        features.push(format!("style_{}", config.settings.output_style));
+    }
+
     let mut system_prompt = build_system_prompt(
         &config.instructions,
         &tool_defs,
@@ -128,37 +135,11 @@ pub fn build_with_frontend(
         &skills_summary,
         &config.memory,
         start.agent_type.as_deref(),
+        features,
     );
 
-    // Append MCP server instructions (from initialize handshake).
-    let mcp_instructions = kernel.mcp_instructions();
-    if !mcp_instructions.is_empty() {
-        system_prompt.push_str("\n\n# MCP Server Instructions\n");
-        for (server_name, instructions) in mcp_instructions {
-            system_prompt.push_str(&format!("\n## {server_name}\n{instructions}\n"));
-        }
-    }
-
-    // Append scheduler instructions (every agent has cron capability).
-    system_prompt.push_str(SCHEDULER_PROMPT);
+    crate::prompt_post::append_runtime_sections(&mut system_prompt, &kernel);
 
-    // Append MCP resource and prompt summaries so the LLM knows what's available.
-    let mcp_resources = kernel.mcp_resources();
-    if !mcp_resources.is_empty() {
-        system_prompt.push_str("\n\n# Available MCP Resources\n");
-        for (server, res) in mcp_resources {
-            let desc = res.description.as_deref().unwrap_or("");
-            system_prompt.push_str(&format!("\n- `{}` ({server}): {desc}", res.uri));
-        }
-    }
-    let mcp_prompts = kernel.mcp_prompts();
-    if !mcp_prompts.is_empty() {
-        system_prompt.push_str("\n\n# Available MCP Prompts\n");
-        for (server, p) in mcp_prompts {
-            let desc = p.description.as_deref().unwrap_or("");
-            system_prompt.push_str(&format!("\n- `{}` ({server}): {desc}", p.name));
-        }
-    }
     let mut messages = resume_messages;
     if let Some(prompt) = &start.prompt {
         messages.push(loopal_message::Message::user(prompt));

crates/loopal-agent-server/src/lib.rs

@@ -18,6 +18,7 @@ mod ipc_frontend;
 mod memory_adapter;
 mod mock_loader;
 mod params;
+mod prompt_post;
 mod server;
 pub mod server_info;
 mod server_init;

crates/loopal-agent-server/src/prompt_post.rs

@@ -0,0 +1,40 @@
+//! System prompt post-processing: appends MCP, scheduler, and resource sections.
+
+use loopal_kernel::Kernel;
+
+const SCHEDULER_PROMPT: &str = "\n\n# Scheduled Messages\n\
+    Messages prefixed with `[scheduled]` are injected by the cron scheduler, \
+    not typed by the user. Treat them as automated prompts and execute the \
+    requested action without asking for confirmation. \
+    Use CronCreate/CronDelete/CronList tools to manage scheduled jobs.";
+
+/// Append MCP instructions, scheduler guidance, and resource/prompt summaries.
+pub fn append_runtime_sections(prompt: &mut String, kernel: &Kernel) {
+    let mcp_instructions = kernel.mcp_instructions();
+    if !mcp_instructions.is_empty() {
+        prompt.push_str("\n\n# MCP Server Instructions\n");
+        for (server_name, instructions) in mcp_instructions {
+            prompt.push_str(&format!("\n## {server_name}\n{instructions}\n"));
+        }
+    }
+
+    prompt.push_str(SCHEDULER_PROMPT);
+
+    let mcp_resources = kernel.mcp_resources();
+    if !mcp_resources.is_empty() {
+        prompt.push_str("\n\n# Available MCP Resources\n");
+        for (server, res) in mcp_resources {
+            let desc = res.description.as_deref().unwrap_or("");
+            prompt.push_str(&format!("\n- `{}` ({server}): {desc}", res.uri));
+        }
+    }
+
+    let mcp_prompts = kernel.mcp_prompts();
+    if !mcp_prompts.is_empty() {
+        prompt.push_str("\n\n# Available MCP Prompts\n");
+        for (server, p) in mcp_prompts {
+            let desc = p.description.as_deref().unwrap_or("");
+            prompt.push_str(&format!("\n- `{}` ({server}): {desc}", p.name));
+        }
+    }
+}

crates/loopal-config/src/settings.rs

@@ -57,6 +57,10 @@ pub struct Settings {
     /// Harness control parameters — configurable thresholds for the agent control loop.
     #[serde(default)]
     pub harness: HarnessConfig,
+
+    /// Output style override (e.g. "explanatory", "learning"). Empty = default.
+    #[serde(default)]
+    pub output_style: String,
 }
 
 impl Default for Settings {
@@ -74,6 +78,7 @@ impl Default for Settings {
             thinking: ThinkingConfig::default(),
             memory: MemoryConfig::default(),
             harness: HarnessConfig::default(),
+            output_style: String::new(),
         }
     }
 }

crates/loopal-context/src/system_prompt.rs

@@ -5,6 +5,7 @@ use loopal_prompt_system::system_fragments;
 use loopal_tool_api::ToolDefinition;
 
 /// Build a full system prompt using the fragment-based prompt system.
+#[allow(clippy::too_many_arguments)]
 pub fn build_system_prompt(
     instructions: &str,
     tools: &[ToolDefinition],
@@ -13,6 +14,7 @@ pub fn build_system_prompt(
     skills_summary: &str,
     memory: &str,
     agent_type: Option<&str>,
+    features: Vec<String>,
 ) -> String {
     let mut registry = FragmentRegistry::new(system_fragments());
 
@@ -49,7 +51,7 @@ pub fn build_system_prompt(
         instructions: instructions.to_string(),
         memory: memory.to_string(),
         skills_summary: skills_summary.to_string(),
-        features: Vec::new(),
+        features,
         agent_name: None,
         agent_type: agent_type.map(String::from),
     };

crates/loopal-context/tests/suite/system_prompt_agent_test.rs

@@ -28,6 +28,7 @@ fn explore_subagent_full_prompt() {
         "",
         "",
         Some("explore"),
+        vec![],
     );
 
     // Explore-specific content present
@@ -61,7 +62,7 @@ fn explore_subagent_full_prompt() {
 
 #[test]
 fn root_agent_excludes_agent_fragments() {
-    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None);
+    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None, vec![]);
     // No agent fragments in root prompt
     assert!(
         !result.contains("sub-agent named"),
@@ -77,7 +78,7 @@ fn root_agent_excludes_agent_fragments() {
 
 #[test]
 fn plan_subagent_gets_plan_fragment() {
-    let result = build_system_prompt("", &[], "act", "/work", "", "", Some("plan"));
+    let result = build_system_prompt("", &[], "act", "/work", "", "", Some("plan"), vec![]);
     assert!(
         result.contains("software architect"),
         "plan fragment should be included"
@@ -94,7 +95,7 @@ fn plan_subagent_gets_plan_fragment() {
 
 #[test]
 fn general_subagent_gets_default_fragment() {
-    let result = build_system_prompt("", &[], "act", "/work", "", "", Some("general"));
+    let result = build_system_prompt("", &[], "act", "/work", "", "", Some("general"), vec![]);
     // Default sub-agent fragment (fallback for unknown types)
     assert!(
         result.contains("sub-agent named"),

crates/loopal-context/tests/suite/system_prompt_test.rs

@@ -3,7 +3,7 @@ use loopal_tool_api::ToolDefinition;
 
 #[test]
 fn includes_instructions() {
-    let result = build_system_prompt("You are helpful.", &[], "act", "/tmp", "", "", None);
+    let result = build_system_prompt("You are helpful.", &[], "act", "/tmp", "", "", None, vec![]);
     assert!(result.contains("You are helpful."));
 }
 
@@ -14,7 +14,7 @@ fn tool_schemas_not_in_system_prompt() {
         description: "Read a file".into(),
         input_schema: serde_json::json!({"type": "object"}),
     }];
-    let result = build_system_prompt("Base", &tools, "act", "/workspace", "", "", None);
+    let result = build_system_prompt("Base", &tools, "act", "/workspace", "", "", None, vec![]);
     // Tool schemas should NOT appear in system prompt — they go via ChatParams.tools
     assert!(!result.contains("# Available Tools"));
     assert!(!result.contains("## read"));
@@ -24,7 +24,7 @@ fn tool_schemas_not_in_system_prompt() {
 
 #[test]
 fn includes_fragments() {
-    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None);
+    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None, vec![]);
     // Core fragments should be present
     assert!(
         result.contains("Output Efficiency"),
@@ -47,7 +47,8 @@ fn cwd_available_in_subagent_prompt() {
         "/Users/dev/project",
         "",
         "",
-        Some("general"), // any agent_type makes is_subagent() true
+        Some("general"),
+        vec![],
     );
     assert!(
         result.contains("/Users/dev/project"),
@@ -58,7 +59,7 @@ fn cwd_available_in_subagent_prompt() {
 #[test]
 fn includes_skills() {
     let skills = "# Available Skills\n- /commit: Generate a git commit message";
-    let result = build_system_prompt("Base", &[], "act", "/workspace", skills, "", None);
+    let result = build_system_prompt("Base", &[], "act", "/workspace", skills, "", None, vec![]);
     assert!(result.contains("Available Skills"));
     assert!(result.contains("/commit"));
 }
@@ -73,14 +74,15 @@ fn includes_memory() {
         "",
         "## Key Patterns\n- Use DI",
         None,
+        vec![],
     );
     assert!(result.contains("# Project Memory"));
     assert!(result.contains("Key Patterns"));
 }
 
 #[test]
 fn empty_memory_no_section() {
-    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None);
+    let result = build_system_prompt("Base", &[], "act", "/workspace", "", "", None, vec![]);
     assert!(!result.contains("Project Memory"));
 }
 
@@ -92,20 +94,95 @@ fn tool_conditional_fragments() {
         description: "Execute commands".into(),
         input_schema: serde_json::json!({"type": "object"}),
     }];
-    let result = build_system_prompt("Base", &tools, "act", "/workspace", "", "", None);
+    let result = build_system_prompt("Base", &tools, "act", "/workspace", "", "", None, vec![]);
     assert!(
         result.contains("Bash Tool Guidelines"),
         "bash guidelines missing when Bash tool present"
     );
 
     // Without Bash tool → no bash guidelines
-    let result_no_bash = build_system_prompt("Base", &[], "act", "/workspace", "", "", None);
+    let result_no_bash =
+        build_system_prompt("Base", &[], "act", "/workspace", "", "", None, vec![]);
     assert!(
         !result_no_bash.contains("Bash Tool Guidelines"),
         "bash guidelines should not appear without Bash"
     );
 }
 
+#[test]
+fn feature_conditional_fragments() {
+    // With "memory" feature → memory guidance should appear
+    let with_memory = build_system_prompt(
+        "Base",
+        &[],
+        "act",
+        "/workspace",
+        "",
+        "",
+        None,
+        vec!["memory".into()],
+    );
+    assert!(
+        with_memory.contains("Memory System"),
+        "memory guidance fragment missing when memory feature enabled"
+    );
+
+    // Without "memory" feature → no memory guidance
+    let without = build_system_prompt("Base", &[], "act", "/workspace", "", "", None, vec![]);
+    assert!(
+        !without.contains("Memory System"),
+        "memory guidance should not appear without memory feature"
+    );
+
+    // With "hooks" feature → hooks guidance should appear
+    let with_hooks = build_system_prompt(
+        "Base",
+        &[],
+        "act",
+        "/workspace",
+        "",
+        "",
+        None,
+        vec!["hooks".into()],
+    );
+    assert!(
+        with_hooks.contains("hooks"),
+        "hooks fragment missing when hooks feature enabled"
+    );
+
+    // With style feature → style fragment should appear
+    let with_style = build_system_prompt(
+        "Base",
+        &[],
+        "act",
+        "/workspace",
+        "",
+        "",
+        None,
+        vec!["style_explanatory".into()],
+    );
+    assert!(
+        with_style.contains("Explanatory"),
+        "explanatory style fragment missing when style feature enabled"
+    );
+
+    // With "subagent" feature → agent guidelines should appear
+    let with_subagent = build_system_prompt(
+        "Base",
+        &[],
+        "act",
+        "/workspace",
+        "",
+        "",
+        None,
+        vec!["subagent".into()],
+    );
+    assert!(
+        with_subagent.contains("Sub-Agent Usage"),
+        "agent guidelines fragment missing when subagent feature enabled"
+    );
+}
+
 #[test]
 fn report_token_usage() {
     use loopal_context::estimate_tokens;
@@ -152,10 +229,11 @@ fn report_token_usage() {
     let mem = "## Architecture\n- 17 Rust crates\n- 200-line limit";
     let skills = "# Available Skills\n- /commit: Git commit\n- /review-pr: Review PR";
 
-    let bare = build_system_prompt("", &[], "act", "/project", "", "", None);
-    let with_tools = build_system_prompt("", &tools, "act", "/project", "", "", None);
-    let full_act = build_system_prompt(instr, &tools, "act", "/project", skills, mem, None);
-    let full_plan = build_system_prompt(instr, &tools, "plan", "/project", skills, mem, None);
+    let bare = build_system_prompt("", &[], "act", "/project", "", "", None, vec![]);
+    let with_tools = build_system_prompt("", &tools, "act", "/project", "", "", None, vec![]);
+    let full_act = build_system_prompt(instr, &tools, "act", "/project", skills, mem, None, vec![]);
+    let full_plan =
+        build_system_prompt(instr, &tools, "plan", "/project", skills, mem, None, vec![]);
 
     let t_bare = estimate_tokens(&bare);
     let t_tools = estimate_tokens(&with_tools);