fix(ai): replay openrouter deepseek reasoning content

Normalized OpenRouter reasoning replay back to DeepSeek's required reasoning_content field for exact-replay providers.

Added regression coverage for OpenRouter DeepSeek V4 tool-call continuations.

Fixes #1445

packages/ai/CHANGELOG.md

@@ -11,6 +11,10 @@
 - `OpenAIResponsesOptions` gains four optional, provider-agnostic fields that adapter wrappers can use to compose provider-specific behavior on top of the generic transport: `includeEncryptedReasoning` (gates `include: ["reasoning.encrypted_content"]`; default `true`, preserves current behavior), `filterReasoningHistory` (strips replayed `type: "reasoning"` items from conversation history; default `false`), `headers` (merged onto the client's default headers), and `extraBody` (merged into the request payload).
 - The existing `XAI_API_KEY` path is unchanged — it continues to use the OpenAI-completions transport.
 
+### Fixed
+
+- Fixed OpenRouter DeepSeek V4 tool-call follow-up requests replaying normalized `reasoning` as-is instead of DeepSeek's required `reasoning_content`, which caused HTTP 400 errors in thinking mode. ([#1445](https://github.com/can1357/oh-my-pi/issues/1445))
+
 ## [15.5.6] - 2026-05-27
 ### Added
 

packages/ai/src/providers/openai-completions.ts

@@ -1507,12 +1507,13 @@ export function convertMessages(
 				}
 			}
 
-			if (compat.thinkingFormat === "openai" && compat.requiresReasoningContentForToolCalls) {
+			if (compat.requiresReasoningContentForToolCalls) {
 				const streamedReasoningField = nonEmptyThinkingBlocks[0]?.thinkingSignature;
 				const reasoningField =
-					streamedReasoningField === "reasoning_content" ||
-					streamedReasoningField === "reasoning" ||
-					streamedReasoningField === "reasoning_text"
+					compat.allowsSyntheticReasoningContentForToolCalls &&
+					(streamedReasoningField === "reasoning_content" ||
+						streamedReasoningField === "reasoning" ||
+						streamedReasoningField === "reasoning_text")
 						? streamedReasoningField
 						: (compat.reasoningContentField ?? "reasoning_content");
 				const reasoningContent = (assistantMsg as any)[reasoningField];
@@ -1547,9 +1548,9 @@ export function convertMessages(
 				(compat.thinkingFormat === "openai" ||
 					compat.thinkingFormat === "openrouter" ||
 					compat.thinkingFormat === "zai");
-			// DeepSeek reasoning models require reasoning_content on ALL assistant turns,
-			// not just tool-call turns. Other providers (Kimi, OpenRouter) only require it
-			// on tool-call turns.
+			// DeepSeek-compatible reasoning models require reasoning_content on all
+			// assistant turns. Providers that allow placeholders only need it on
+			// tool-call turns.
 			const needsReasoningOnAllTurns =
 				compat.requiresReasoningContentForToolCalls && !compat.allowsSyntheticReasoningContentForToolCalls;
 			const needsReasoningField = needsReasoningOnAllTurns || toolCalls.length > 0;
@@ -1576,7 +1577,8 @@ export function convertMessages(
 					const signature = allThinkingBlocks[0].thinkingSignature;
 					const recognizedFields = ["reasoning_content", "reasoning", "reasoning_text"];
 					if (signature && recognizedFields.includes(signature)) {
-						(assistantMsg as any)[signature] = allThinkingBlocks.map(b => b.thinking).join("\n");
+						const reasoningField = compat.reasoningContentField ?? "reasoning_content";
+						(assistantMsg as any)[reasoningField] = allThinkingBlocks.map(b => b.thinking).join("\n");
 						hasReasoningField = true;
 					}
 				}

packages/ai/test/deepseek-reasoning-content.test.ts

@@ -242,6 +242,31 @@ describe("DeepSeek reasoning_content tool-call replay", () => {
 			expect(assistant).toBeDefined();
 			expect(Reflect.get(assistant as object, "reasoning_content")).toBe("I need to read the file first.");
 		});
+
+		it("normalizes OpenRouter reasoning deltas to DeepSeek reasoning_content on replay", () => {
+			const model = getBundledModel("openrouter", "deepseek/deepseek-v4-pro") as Model<"openai-completions">;
+			const compat = detectCompat(model);
+			expect(compat.requiresReasoningContentForToolCalls).toBe(true);
+			expect(compat.allowsSyntheticReasoningContentForToolCalls).toBe(false);
+
+			const msg = assistantToolCall(model, [
+				{
+					type: "thinking",
+					thinking: "I should inspect the requested file.",
+					thinkingSignature: "reasoning",
+				} as ThinkingContent,
+				{
+					type: "toolCall",
+					id: "call_openrouter_deepseek",
+					name: "read",
+					arguments: { path: "package.json" },
+				} as ToolCall,
+			]);
+			const messages = convertMessages(model, { messages: [msg] }, compat);
+			const assistant = messages.find(m => m.role === "assistant");
+			expect(assistant).toBeDefined();
+			expect(Reflect.get(assistant as object, "reasoning_content")).toBe("I should inspect the requested file.");
+		});
 		it("does not use opaque signature as property name but still sets reasoning_content from thinking text", () => {
 			const model = deepseekModel({
 				provider: "opencode-go",