From ca0bd53bede259c78f78bd4f0ab10303ea3c8b0b Mon Sep 17 00:00:00 2001
From: Bennet Bo Fenner <bennet@zed.dev>
Date: Mon, 30 Jun 2025 11:31:40 +0200
Subject: [PATCH] agent: Fix an issue with messages containing trailing
 whitespace (#33643)

Seeing this come up in our server logs when sending requests to
Anthropic: `final assistant content cannot end with trailing
whitespace`.


Release Notes:

- agent: Fixed an issue where Anthropic requests would sometimes fail
because of malformed assistant messages
---
 crates/agent/src/thread.rs                       | 1 +
 crates/language_models/src/provider/anthropic.rs | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/crates/agent/src/thread.rs b/crates/agent/src/thread.rs
index 32c376ca67..2f965e232a 100644
--- a/crates/agent/src/thread.rs
+++ b/crates/agent/src/thread.rs
@@ -1343,6 +1343,7 @@ impl Thread {
             for segment in &message.segments {
                 match segment {
                     MessageSegment::Text(text) => {
+                        let text = text.trim_end();
                         if !text.is_empty() {
                             request_message
                                 .content
diff --git a/crates/language_models/src/provider/anthropic.rs b/crates/language_models/src/provider/anthropic.rs
index 48bea47fec..aa500f4b4d 100644
--- a/crates/language_models/src/provider/anthropic.rs
+++ b/crates/language_models/src/provider/anthropic.rs
@@ -528,6 +528,11 @@ pub fn into_anthropic(
                     .into_iter()
                     .filter_map(|content| match content {
                         MessageContent::Text(text) => {
+                            let text = if text.chars().last().map_or(false, |c| c.is_whitespace()) {
+                                text.trim_end().to_string()
+                            } else {
+                                text
+                            };
                             if !text.is_empty() {
                                 Some(anthropic::RequestContent::Text {
                                     text,