agent: Handle context window exceeded errors from Anthropic (#28688)

![CleanShot 2025-04-14 at 11 15
38@2x](https://github.com/user-attachments/assets/9e803ffb-74fd-486b-bebc-2155a407a9fa)

Release Notes:

- agent: Handle context window exceeded errors from Anthropic

crates/language_models/src/provider/cloud.rs

@@ -1,4 +1,4 @@
-use anthropic::{AnthropicError, AnthropicModelMode};
+use anthropic::{AnthropicError, AnthropicModelMode, parse_prompt_too_long};
 use anyhow::{Result, anyhow};
 use client::{
     Client, EXPIRED_LLM_TOKEN_HEADER_NAME, MAX_LLM_MONTHLY_SPEND_REACHED_HEADER_NAME,
@@ -14,7 +14,7 @@ use gpui::{AnyElement, AnyView, App, AsyncApp, Context, Entity, Subscription, Ta
 use http_client::{AsyncBody, HttpClient, Method, Response, StatusCode};
 use language_model::{
     AuthenticateError, CloudModel, LanguageModel, LanguageModelCacheConfiguration, LanguageModelId,
-    LanguageModelName, LanguageModelProviderId, LanguageModelProviderName,
+    LanguageModelKnownError, LanguageModelName, LanguageModelProviderId, LanguageModelProviderName,
     LanguageModelProviderState, LanguageModelProviderTosView, LanguageModelRequest,
     LanguageModelToolSchemaFormat, RateLimiter, ZED_CLOUD_PROVIDER_ID,
 };
@@ -33,6 +33,7 @@ use std::{
     time::Duration,
 };
 use strum::IntoEnumIterator;
+use thiserror::Error;
 use ui::{TintColor, prelude::*};
 
 use crate::AllLanguageModelSettings;
@@ -575,14 +576,19 @@ impl CloudLanguageModel {
             } else {
                 let mut body = String::new();
                 response.body_mut().read_to_string(&mut body).await?;
-                return Err(anyhow!(
-                    "cloud language model completion failed with status {status}: {body}",
-                ));
+                return Err(anyhow!(ApiError { status, body }));
             }
         }
     }
 }
 
+#[derive(Debug, Error)]
+#[error("cloud language model completion failed with status {status}: {body}")]
+struct ApiError {
+    status: StatusCode,
+    body: String,
+}
+
 impl LanguageModel for CloudLanguageModel {
     fn id(&self) -> LanguageModelId {
         self.id.clone()
@@ -696,7 +702,23 @@ impl LanguageModel for CloudLanguageModel {
                             )?)?,
                         },
                     )
-                    .await?;
+                    .await
+                    .map_err(|err| match err.downcast::<ApiError>() {
+                        Ok(api_err) => {
+                            if api_err.status == StatusCode::BAD_REQUEST {
+                                if let Some(tokens) = parse_prompt_too_long(&api_err.body) {
+                                    return anyhow!(
+                                        LanguageModelKnownError::ContextWindowLimitExceeded {
+                                            tokens
+                                        }
+                                    );
+                                }
+                            }
+                            anyhow!(api_err)
+                        }
+                        Err(err) => anyhow!(err),
+                    })?;
+
                     Ok(
                         crate::provider::anthropic::map_to_language_model_completion_events(
                             Box::pin(response_lines(response).map_err(AnthropicError::Other)),