feat: async research tool - runs in background, returns immediately

The research tool now spawns the scout agent in a background tokio task
and returns immediately with a research_id placeholder. This allows the
agent to continue working while research runs (30-120 seconds).

Key changes:
- New PendingResearchManager for tracking async research tasks
- research tool returns immediately with placeholder containing research_id
- research_status tool to check progress of pending research
- Auto-injection of completed research at natural break points:
  - Start of each tool iteration (before LLM call)
  - Before prompting user in interactive mode
- /research CLI command to list all research tasks
- Updated system prompt to explain async behavior

The agent can:
- Continue with other work while research runs
- Check status with research_status tool
- Yield turn to user if results are critical before continuing

crates/g3-core/src/tool_definitions.rs

@@ -258,7 +258,7 @@ fn create_core_tools(exclude_research: bool) -> Vec<Tool> {
     if !exclude_research {
         tools.push(Tool {
             name: "research".to_string(),
-            description: "Perform web-based research on a topic and return a structured research brief. Use this tool when you need to research APIs, SDKs, libraries, approaches, bugs, documentation, or anything else that requires web-based research. The tool spawns a specialized research agent that browses the web and returns a concise, decision-ready report.".to_string(),
+            description: "Initiate web-based research on a topic. This tool is ASYNCHRONOUS - it spawns a research agent in the background and returns immediately with a research_id. Results are automatically injected into the conversation when ready. Use this when you need to research APIs, SDKs, libraries, approaches, bugs, or documentation. If you need the results before continuing, say so and yield the turn to the user. Check status with research_status tool.".to_string(),
             input_schema: json!({
                 "type": "object",
                 "properties": {
@@ -270,6 +270,22 @@ fn create_core_tools(exclude_research: bool) -> Vec<Tool> {
                 "required": ["query"]
             }),
         });
+
+        // research_status tool - check status of pending research
+        tools.push(Tool {
+            name: "research_status".to_string(),
+            description: "Check the status of pending research tasks. Call without arguments to list all pending research, or with a research_id to check a specific task. Use this to see if research has completed before it's automatically injected.".to_string(),
+            input_schema: json!({
+                "type": "object",
+                "properties": {
+                    "research_id": {
+                        "type": "string",
+                        "description": "Optional: specific research_id to check. If omitted, lists all pending research tasks."
+                    }
+                },
+                "required": []
+            }),
+        });
     }
 
     // Workspace memory tool (memory is auto-loaded at startup, only remember is needed)
@@ -509,9 +525,9 @@ mod tests {
         let tools = create_core_tools(false);
         // Should have the core tools: shell, background_process, read_file, read_image,
         // write_file, str_replace, screenshot,
-        // todo_read, todo_write, coverage, code_search, research, remember
-        // (13 total - memory is auto-loaded, only remember tool needed)
-        assert_eq!(tools.len(), 14);
+        // todo_read, todo_write, coverage, code_search, research, research_status, remember
+        // (15 total - memory is auto-loaded, only remember tool needed)
+        assert_eq!(tools.len(), 15);
     }
 
     #[test]
@@ -525,15 +541,15 @@ mod tests {
     fn test_create_tool_definitions_core_only() {
         let config = ToolConfig::default();
         let tools = create_tool_definitions(config);
-        assert_eq!(tools.len(), 14);
+        assert_eq!(tools.len(), 15);
     }
 
     #[test]
     fn test_create_tool_definitions_all_enabled() {
         let config = ToolConfig::new(true, true);
         let tools = create_tool_definitions(config);
-        // 13 core + 15 webdriver = 28
-        assert_eq!(tools.len(), 29);
+        // 15 core + 15 webdriver = 30
+        assert_eq!(tools.len(), 30);
     }
 
     #[test]
@@ -551,8 +567,8 @@ mod tests {
         let tools_with_research = create_core_tools(false);
         let tools_without_research = create_core_tools(true);
         
-        assert_eq!(tools_with_research.len(), 14);
-        assert_eq!(tools_without_research.len(), 13);
+        assert_eq!(tools_with_research.len(), 15);
+        assert_eq!(tools_without_research.len(), 13);  // research + research_status both excluded
         
         assert!(tools_with_research.iter().any(|t| t.name == "research"));
         assert!(!tools_without_research.iter().any(|t| t.name == "research"));