Adjust error messages (#1969)

<img width="1378" height="285" alt="image"
src="https://github.com/user-attachments/assets/f0283378-f839-4a1f-8331-909694a04b1f"
/>

codex-rs/core/src/error.rs

@@ -62,14 +62,16 @@ pub enum CodexErr {
     #[error("unexpected status {0}: {1}")]
     UnexpectedStatus(StatusCode, String),
 
-    #[error("Usage limit has been reached")]
-    UsageLimitReached,
+    #[error("{0}")]
+    UsageLimitReached(UsageLimitReachedError),
 
-    #[error("Usage not included with the plan")]
+    #[error(
+        "To use Codex with your ChatGPT plan, upgrade to Plus: https://openai.com/chatgpt/pricing."
+    )]
     UsageNotIncluded,
 
     #[error(
-        "We’re currently experiencing high demand, which may cause temporary errors. We’re adding capacity in East and West Europe to restore normal service."
+        "We're currently experiencing high demand, which may cause temporary errors. We’re adding capacity in East and West Europe to restore normal service."
     )]
     InternalServerError,
 
@@ -115,6 +117,30 @@ pub enum CodexErr {
     EnvVar(EnvVarError),
 }
 
+#[derive(Debug)]
+pub struct UsageLimitReachedError {
+    pub plan_type: Option<String>,
+}
+
+impl std::fmt::Display for UsageLimitReachedError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if let Some(plan_type) = &self.plan_type
+            && plan_type == "plus"
+        {
+            write!(
+                f,
+                "You've hit your usage limit. Upgrade to Pro (https://openai.com/chatgpt/pricing), or wait for limits to reset (every 5h and every week.)."
+            )?;
+        } else {
+            write!(
+                f,
+                "You've hit usage your usage limit. Limits reset every 5h and every week."
+            )?;
+        }
+        Ok(())
+    }
+}
+
 #[derive(Debug)]
 pub struct EnvVarError {
     /// Name of the environment variable that is missing.
@@ -150,3 +176,39 @@ pub fn get_error_message_ui(e: &CodexErr) -> String {
         _ => e.to_string(),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn usage_limit_reached_error_formats_plus_plan() {
+        let err = UsageLimitReachedError {
+            plan_type: Some("plus".to_string()),
+        };
+        assert_eq!(
+            err.to_string(),
+            "You've hit your usage limit. Upgrade to Pro (https://openai.com/chatgpt/pricing), or wait for limits to reset (every 5h and every week.)."
+        );
+    }
+
+    #[test]
+    fn usage_limit_reached_error_formats_default_when_none() {
+        let err = UsageLimitReachedError { plan_type: None };
+        assert_eq!(
+            err.to_string(),
+            "You've hit usage your usage limit. Limits reset every 5h and every week."
+        );
+    }
+
+    #[test]
+    fn usage_limit_reached_error_formats_default_for_other_plans() {
+        let err = UsageLimitReachedError {
+            plan_type: Some("pro".to_string()),
+        };
+        assert_eq!(
+            err.to_string(),
+            "You've hit usage your usage limit. Limits reset every 5h and every week."
+        );
+    }
+}