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/anthropic/src/anthropic.rs

@@ -507,6 +507,15 @@ pub enum RequestContent {
         #[serde(skip_serializing_if = "Option::is_none")]
         cache_control: Option<CacheControl>,
     },
+    #[serde(rename = "thinking")]
+    Thinking {
+        thinking: String,
+        signature: String,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        cache_control: Option<CacheControl>,
+    },
+    #[serde(rename = "redacted_thinking")]
+    RedactedThinking { data: String },
     #[serde(rename = "image")]
     Image {
         source: ImageSource,