agent: Preserve thinking blocks between requests (#29055)

Looks like the required backend component of this was deployed.

https://github.com/zed-industries/monorepo/actions/runs/14541199197

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Agus Zubiaga <hi@aguz.me>
Co-authored-by: Richard Feldman <oss@rtfeldman.com>
Co-authored-by: Nathan Sobo <nathan@zed.dev>

crates/language_models/src/provider/copilot_chat.rs

@@ -424,8 +424,11 @@ impl CopilotChatLanguageModel {
             let text_content = {
                 let mut buffer = String::new();
                 for string in message.content.iter().filter_map(|content| match content {
-                    MessageContent::Text(text) => Some(text.as_str()),
+                    MessageContent::Text(text) | MessageContent::Thinking { text, .. } => {
+                        Some(text.as_str())
+                    }
                     MessageContent::ToolUse(_)
+                    | MessageContent::RedactedThinking(_)
                     | MessageContent::ToolResult(_)
                     | MessageContent::Image(_) => None,
                 }) {