Remove legacy logs/ directory, consolidate all data under .g3/

This change removes the legacy logs/ directory and consolidates all
session data, error logs, and discovery files under the .g3/ directory.

New directory structure:
- .g3/sessions/<session_id>/session.json - session logs
- .g3/errors/ - error logs (was logs/errors/)
- .g3/background_processes/ - background process logs
- .g3/discovery/ - planner discovery files (was workspace/logs/)

Changes:
- paths.rs: Remove get_logs_dir()/logs_dir(), add get_errors_dir(),
  get_background_processes_dir(), get_discovery_dir()
- session.rs: Anonymous sessions now use .g3/sessions/anonymous_<ts>/
- error_handling.rs: Errors now saved to .g3/errors/
- project.rs: Remove logs_dir() and ensure_logs_dir() methods
- feedback_extraction.rs: Remove logs_dir field and fallback logic
- planner: Use .g3/ for workspace data and .g3/discovery/ for reports
- flock.rs: Look for session metrics in .g3/sessions/
- coach_feedback.rs: Remove fallback to logs/ path
- Update all tests to use new paths
- Update README.md and .gitignore

crates/g3-cli/src/cli_args.rs

@@ -63,7 +63,7 @@ pub struct Cli {
     #[arg(long, value_name = "MODEL")]
     pub model: Option<String>,
 
-    /// Disable log file creation (no logs/ directory or session logs)
+    /// Disable session log file creation (no .g3/sessions/ or error logs)
     #[arg(long)]
     pub quiet: bool,
 

crates/g3-cli/src/coach_feedback.rs

@@ -54,12 +54,7 @@ pub fn extract_from_logs(
 
 /// Resolve the log file path, trying new path first then falling back to old.
 fn resolve_log_path(session_id: &str) -> std::path::PathBuf {
-    let new_path = g3_core::get_session_file(session_id);
-    if new_path.exists() {
-        new_path
-    } else {
-        Path::new("logs").join(format!("g3_session_{}.json", session_id))
-    }
+    g3_core::get_session_file(session_id)
 }
 
 /// Extract feedback from a session log file.

crates/g3-cli/tests/coach_feedback_extraction_test.rs

@@ -4,15 +4,17 @@ use tempfile::TempDir;
 
 #[test]
 fn test_extract_coach_feedback_with_timing_message() {
-    // Create a temporary directory for logs
+    // Create a temporary directory for session logs
     let temp_dir = TempDir::new().unwrap();
-    let logs_dir = temp_dir.path().join("logs");
-    fs::create_dir(&logs_dir).unwrap();
+    let sessions_dir = temp_dir.path().join(".g3").join("sessions");
+    fs::create_dir_all(&sessions_dir).unwrap();
 
     // Create a mock session log with the problematic conversation history
     // where timing message appears after the tool result
     let session_id = "test_session_123";
-    let log_file_path = logs_dir.join(format!("g3_session_{}.json", session_id));
+    let session_dir = sessions_dir.join(session_id);
+    fs::create_dir_all(&session_dir).unwrap();
+    let log_file_path = session_dir.join("session.json");
 
     let log_content = json!({
         "session_id": session_id,
@@ -93,11 +95,13 @@ fn test_extract_coach_feedback_with_timing_message() {
 fn test_extract_only_final_output_tool_results() {
     // Test that we only extract tool results from final_output, not from other tools
     let temp_dir = TempDir::new().unwrap();
-    let logs_dir = temp_dir.path().join("logs");
-    fs::create_dir(&logs_dir).unwrap();
+    let sessions_dir = temp_dir.path().join(".g3").join("sessions");
+    fs::create_dir_all(&sessions_dir).unwrap();
 
     let session_id = "test_session_final_output_only";
-    let log_file_path = logs_dir.join(format!("g3_session_{}.json", session_id));
+    let session_dir = sessions_dir.join(session_id);
+    fs::create_dir_all(&session_dir).unwrap();
+    let log_file_path = session_dir.join("session.json");
 
     let log_content = json!({
         "session_id": session_id,
@@ -184,14 +188,16 @@ fn test_extract_only_final_output_tool_results() {
 
 #[test]
 fn test_extract_coach_feedback_without_timing_message() {
-    // Create a temporary directory for logs
+    // Create a temporary directory for session logs
     let temp_dir = TempDir::new().unwrap();
-    let logs_dir = temp_dir.path().join("logs");
-    fs::create_dir(&logs_dir).unwrap();
+    let sessions_dir = temp_dir.path().join(".g3").join("sessions");
+    fs::create_dir_all(&sessions_dir).unwrap();
 
     // Test the case where there's no timing message (backward compatibility)
     let session_id = "test_session_456";
-    let log_file_path = logs_dir.join(format!("g3_session_{}.json", session_id));
+    let session_dir = sessions_dir.join(session_id);
+    fs::create_dir_all(&session_dir).unwrap();
+    let log_file_path = session_dir.join("session.json");
 
     let log_content = json!({
         "session_id": session_id,
@@ -256,11 +262,13 @@ fn test_extract_coach_feedback_without_timing_message() {
 fn test_extract_coach_feedback_with_multiple_tool_results() {
     // Test that we get the LAST tool result when there are multiple
     let temp_dir = TempDir::new().unwrap();
-    let logs_dir = temp_dir.path().join("logs");
-    fs::create_dir(&logs_dir).unwrap();
+    let sessions_dir = temp_dir.path().join(".g3").join("sessions");
+    fs::create_dir_all(&sessions_dir).unwrap();
 
     let session_id = "test_session_789";
-    let log_file_path = logs_dir.join(format!("g3_session_{}.json", session_id));
+    let session_dir = sessions_dir.join(session_id);
+    fs::create_dir_all(&session_dir).unwrap();
+    let log_file_path = session_dir.join("session.json");
 
     let log_content = json!({
         "session_id": session_id,