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/agent/src/thread_store.rs

@@ -660,9 +660,18 @@ pub struct SerializedMessage {
 #[serde(tag = "type")]
 pub enum SerializedMessageSegment {
     #[serde(rename = "text")]
-    Text { text: String },
+    Text {
+        text: String,
+    },
     #[serde(rename = "thinking")]
-    Thinking { text: String },
+    Thinking {
+        text: String,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        signature: Option<String>,
+    },
+    RedactedThinking {
+        data: Vec<u8>,
+    },
 }
 
 #[derive(Debug, Serialize, Deserialize)]