fix(chat): drop interrupted partial assistant text on cancel; ensure backend removes in-flight say:"text" so UI hydration doesn’t retain it; all tests passing

Author: daniel-lxs

src/core/task/Task.ts

@@ -2025,14 +2025,28 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 						await this.diffViewProvider.revertChanges() // closes diff view
 					}
 
-					// if last message is a partial we need to update and save it
-					const lastMessage = this.clineMessages.at(-1)
-
-					if (lastMessage && lastMessage.partial) {
-						// lastMessage.ts = Date.now() DO NOT update ts since it is used as a key for virtuoso list
-						lastMessage.partial = false
-						// instead of streaming partialMessage events, we do a save and post like normal to persist to disk
-						console.log("updating partial message", lastMessage)
+					// Remove partial streaming messages (text and reasoning) when stream is aborted
+					// to match main branch behavior where interrupted streaming text doesn't persist
+					while (this.clineMessages.length > 0) {
+						const lastMessage = this.clineMessages[this.clineMessages.length - 1]
+
+						if (lastMessage && lastMessage.partial) {
+							// Remove partial text and reasoning messages that were being streamed
+							if (
+								lastMessage.type === "say" &&
+								(lastMessage.say === "text" || lastMessage.say === "reasoning")
+							) {
+								this.clineMessages.pop()
+								console.log(`[abortStream] removed partial ${lastMessage.say} message`)
+								continue
+							}
+
+							// For other partial messages (like tool asks), finalize them instead of removing
+							lastMessage.partial = false
+							console.log(`[abortStream] finalized partial ${lastMessage.type} message`)
+						}
+
+						break
 					}
 
 					// Update `api_req_started` to have cancelled and cost, so that