fix(delegate): respect chat.defaultAgent setting when no agent is specified

When the delegate tool is invoked without an explicit agent name, it
was unconditionally falling back to the hardcoded DEFAULT_AGENT_NAME
("q_cli_default"), ignoring the user's chat.defaultAgent setting.

Fix the fallback chain to:
  1. Use the explicitly provided agent name (unchanged)
  2. Fall back to chat.defaultAgent setting if set
  3. Fall back to DEFAULT_AGENT_NAME as last resort

Fixes #3174

Author: sandikodev

crates/chat-cli/src/cli/chat/tools/delegate.rs

@@ -36,6 +36,7 @@ use crate::cli::{
     Agent,
     DEFAULT_AGENT_NAME,
 };
+use crate::database::settings::Setting;
 use crate::os::Os;
 use crate::theme::StyledText;
 use crate::util::env_var::get_all_env_vars;
@@ -99,7 +100,14 @@ impl Delegate {
                     .as_ref()
                     .ok_or(eyre::eyre!("Task description is required for launch operation"))?;
 
-                let agent_name = self.agent.as_deref().unwrap_or(DEFAULT_AGENT_NAME);
+                // Respect chat.defaultAgent setting before falling back to the hardcoded default.
+                // See: #3174
+                let configured_default = os.database.settings.get_string(Setting::ChatDefaultAgent);
+                let agent_name = self
+                    .agent
+                    .as_deref()
+                    .or(configured_default.as_deref())
+                    .unwrap_or(DEFAULT_AGENT_NAME);
 
                 launch_agent(os, agent_name, agents, task).await?
             },