fix(cursor): degrade K3 same-model history missing thinking

assertCursorKimiK3HistoryReplayable threw for any assistant turn lacking a
non-empty thinking block, including same-model kimi-k3 turns whose stream
carried no thinkingDelta events. Such a turn is persisted with only
text/toolCall blocks, so every subsequent turn failed locally before any
request, permanently bricking the session.

Split the two failure modes: foreign history still hard-errors (another
model's turns cannot replay K3 reasoning), but a same-model turn missing
thinking now degrades to a one-time warning and replays without the
reasoning part via buildCursorAssistantContent, which already omits it.

Fixes #7516

packages/ai/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed Cursor `kimi-k3` sessions bricking permanently when a same-model assistant turn was persisted without thinking blocks (a turn whose stream carried no `thinkingDelta` events). `assertCursorKimiK3HistoryReplayable` now only hard-errors on genuinely foreign history; same-model turns missing thinking degrade to a one-time warning and replay without the reasoning part ([#7516](https://github.com/can1357/oh-my-pi/issues/7516)).
+
 ## [17.2.6] - 2026-08-03
 
 ### Added

packages/ai/src/providers/cursor.ts

@@ -144,6 +144,7 @@ import { isKimiK3ModelId } from "@oh-my-pi/pi-catalog/identity";
 import { calculateCost } from "@oh-my-pi/pi-catalog/models";
 import {
 	$env,
+	logger,
 	parseJsonWithRepair,
 	parseStreamingJson,
 	parseStreamingJsonThrottled,
@@ -4113,16 +4114,34 @@ function assertCursorKimiK3HistoryReplayable(
 ): void {
 	if (!targetModelId || !isKimiK3ModelId(targetModelId)) return;
 	const historyEnd = activeUserMessageIndex >= 0 ? activeUserMessageIndex : messages.length;
+	let sawSameModelMissingThinking = false;
 	for (let i = 0; i < historyEnd; i++) {
 		const msg = messages[i];
 		if (msg.role !== "assistant") continue;
 		const isSameCursorModel = msg.api === "cursor-agent" && msg.provider === "cursor" && msg.model === targetModelId;
-		const hasThinking = msg.content.some(item => item.type === "thinking" && item.thinking.length > 0);
-		if (!isSameCursorModel || !hasThinking) {
+		if (!isSameCursorModel) {
+			// Foreign history genuinely cannot replay K3 thinking: another model's
+			// turns carry no K3-signed reasoning to reconstruct, so continuation
+			// is unsafe and must fail hard.
 			throw new AIError.ValidationError(
-				`Cursor ${targetModelId} requires complete same-model thinking history; start a new session instead of continuing history from ${msg.provider}/${msg.model}.`,
+				`Cursor ${targetModelId} cannot continue history from a different model (${msg.provider}/${msg.model}); start a new session.`,
 			);
 		}
+		const hasThinking = msg.content.some(item => item.type === "thinking" && item.thinking.length > 0);
+		if (!hasThinking) sawSameModelMissingThinking = true;
+	}
+	if (sawSameModelMissingThinking) {
+		// A same-model turn whose stream carried no `thinkingDelta` events is
+		// persisted without thinking blocks. `buildCursorAssistantContent` still
+		// replays its text/tool-call structure and simply omits the reasoning
+		// part, so the history remains usable — degrade with a one-time warning
+		// rather than permanently bricking the session. Per Kimi's
+		// preserved-thinking caveat, K3 generation may be less stable across the
+		// affected span.
+		logger.warn(
+			"Cursor kimi-k3 history contains a same-model assistant turn without thinking blocks; replaying without reasoning for that span (generation may be less stable)",
+			{ model: targetModelId },
+		);
 	}
 }
 

packages/ai/test/cursor-exec-handlers.test.ts

@@ -757,10 +757,48 @@ describe("Cursor history encoding", () => {
 		];
 
 		expect(() => buildCursorHistoryForTest(messages, undefined, "kimi-k3-high")).toThrow(
-			"start a new session instead of continuing history from anthropic/claude-4.6-opus-high",
+			"cannot continue history from a different model (anthropic/claude-4.6-opus-high)",
 		);
 	});
 
+	it("replays a same-model K3 turn missing thinking instead of bricking the session", () => {
+		const messages: Context["messages"] = [
+			{ role: "user", content: "Do a big multi-tool task", timestamp: 1 },
+			cursorAssistant(
+				"kimi-k3-high",
+				[{ type: "toolCall", id: "call-read", name: "read", arguments: { path: "package.json" } }],
+				2,
+				"toolUse",
+			),
+			{
+				role: "toolResult",
+				toolCallId: "call-read",
+				toolName: "read",
+				content: [{ type: "text", text: "package contents" }],
+				isError: false,
+				timestamp: 3,
+			},
+			cursorAssistant("kimi-k3-high", [{ type: "text", text: "Done." }], 4),
+			{ role: "user", content: "Continue the same session", timestamp: 5 },
+		];
+
+		const history = buildCursorHistoryForTest(messages, undefined, "kimi-k3-high");
+
+		expect(history.rootPromptMessagesJson).toEqual([
+			{ role: "user", content: [{ type: "text", text: "Do a big multi-tool task" }] },
+			{
+				role: "assistant",
+				content: [{ type: "tool-call", toolCallId: "call-read", toolName: "read", args: { path: "package.json" } }],
+			},
+			{
+				role: "tool",
+				id: "call-read",
+				content: [{ type: "tool-result", toolName: "read", toolCallId: "call-read", result: "package contents" }],
+			},
+			{ role: "assistant", content: [{ type: "text", text: "Done." }] },
+		]);
+	});
+
 	it("keeps non-K3 Cursor thinking out of model-facing history", () => {
 		const messages: Context["messages"] = [
 			{ role: "user", content: "Inspect package.json", timestamp: 1 },