Merge branch 'pr-8118' into HEAD

# Conflicts:
#	packages/ai/scripts/generate-models.ts
#	packages/ai/src/types.ts
#	packages/ai/test/deferred-tools.test.ts
#	packages/coding-agent/docs/custom-provider.md
#	packages/coding-agent/docs/models.md
#	packages/coding-agent/src/core/model-config.ts

packages/ai/README.md

@@ -1459,6 +1459,7 @@ interface OpenAICompletionsCompat {
   maxTokensField?: 'max_completion_tokens' | 'max_tokens';  // Which field name to use (default: max_completion_tokens)
   requiresToolResultName?: boolean;  // Whether tool results require the `name` field (default: false)
   requiresAssistantAfterToolResult?: boolean; // Whether tool results must be followed by an assistant message (default: false)
+  requiresNonNullAssistantContent?: boolean; // Whether replayed assistant messages with no text must send "" instead of null content (default: false)
   requiresThinkingAsText?: boolean;  // Whether thinking blocks must be converted to text (default: false)
   requiresReasoningContentOnAssistantMessages?: boolean; // Whether all replayed assistant messages must include empty reasoning_content when reasoning is enabled (default: auto-detected for DeepSeek)
   thinkingFormat?: 'openai' | 'openrouter' | 'deepseek' | 'together' | 'baseten' | 'zai' | 'qwen' | 'chat-template' | 'qwen-chat-template' | 'string-thinking' | 'ant-ling'; // Format for reasoning param: 'openai' uses reasoning_effort, 'openrouter' uses reasoning: { effort }, 'deepseek' uses thinking: { type } plus reasoning_effort when supported, 'together' uses reasoning: { enabled } plus reasoning_effort when supported, 'baseten' uses configurable chat_template_args plus reasoning_effort when supported, 'zai' uses thinking: { type }, 'qwen' uses enable_thinking, 'chat-template' uses configurable chat_template_kwargs, 'qwen-chat-template' uses chat_template_kwargs.enable_thinking and preserve_thinking, 'string-thinking' uses top-level thinking, 'ant-ling' uses reasoning: { effort } only for mapped efforts (default: openai)

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

@@ -1281,7 +1281,7 @@ export function convertMessages(
 			// Some providers don't accept null content, use empty string instead
 			const assistantMsg: ChatCompletionAssistantMessageParamWithReasoning = {
 				role: "assistant",
-				content: compat.requiresAssistantAfterToolResult ? "" : null,
+				content: compat.requiresAssistantAfterToolResult || compat.requiresNonNullAssistantContent ? "" : null,
 			};
 
 			const assistantTextParts = msg.content
@@ -1645,6 +1645,7 @@ function detectCompat(model: Model<"openai-completions">): ResolvedOpenAIComplet
 		maxTokensField: useMaxTokens ? "max_tokens" : "max_completion_tokens",
 		requiresToolResultName: false,
 		requiresAssistantAfterToolResult: false,
+		requiresNonNullAssistantContent: false,
 		requiresThinkingAsText: false,
 		requiresReasoningContentOnAssistantMessages: isDeepSeek,
 		thinkingFormat: isDeepSeek
@@ -1701,6 +1702,8 @@ function getCompat(model: Model<"openai-completions">): ResolvedOpenAICompletion
 		requiresToolResultName: model.compat.requiresToolResultName ?? detected.requiresToolResultName,
 		requiresAssistantAfterToolResult:
 			model.compat.requiresAssistantAfterToolResult ?? detected.requiresAssistantAfterToolResult,
+		requiresNonNullAssistantContent:
+			model.compat.requiresNonNullAssistantContent ?? detected.requiresNonNullAssistantContent,
 		requiresThinkingAsText: model.compat.requiresThinkingAsText ?? detected.requiresThinkingAsText,
 		requiresReasoningContentOnAssistantMessages:
 			model.compat.requiresReasoningContentOnAssistantMessages ??

packages/ai/src/providers/compat-schema.ts

@@ -232,6 +232,12 @@ const OpenAICompletionsCompatProperties = {
 				"Whether a user message after tool results requires an assistant message in between. Default: auto-detected from URL.",
 		}),
 	),
+	requiresNonNullAssistantContent: opt(
+		bool({
+			description:
+				'Whether replayed assistant messages with no text (e.g. tool-call-only messages) must send "" instead of null content. Default: false.',
+		}),
+	),
 	requiresThinkingAsText: opt(
 		bool({
 			description:

packages/ai/test/openai-completions-non-null-assistant-content.test.ts

@@ -0,0 +1,115 @@
+import { describe, expect, it } from "vitest";
+import { convertMessages } from "../src/api/openai-completions.ts";
+import { getModel, normalizeContext } from "../src/compat.ts";
+import type { AssistantMessage, Model, OpenAICompletionsCompat, Usage } from "../src/types.ts";
+
+const emptyUsage: Usage = {
+	input: 0,
+	output: 0,
+	cacheRead: 0,
+	cacheWrite: 0,
+	totalTokens: 0,
+	cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+};
+
+const baseCompat: Omit<Required<OpenAICompletionsCompat>, "thinkingTokenBudgetField" | "vllmPriority"> & {
+	thinkingTokenBudgetField?: OpenAICompletionsCompat["thinkingTokenBudgetField"];
+} = {
+	supportsStore: true,
+	supportsDeveloperRole: true,
+	supportsReasoningEffort: true,
+	supportsUsageInStreaming: true,
+	supportsFinishReason: true,
+	maxTokensField: "max_completion_tokens",
+	requiresToolResultName: false,
+	requiresAssistantAfterToolResult: false,
+	requiresNonNullAssistantContent: false,
+	requiresThinkingAsText: false,
+	requiresReasoningContentOnAssistantMessages: false,
+	thinkingFormat: "openai",
+	openRouterRouting: {},
+	vercelGatewayRouting: {},
+	chatTemplateKwargs: {},
+	chatTemplateArgs: {},
+	zaiToolStream: false,
+	supportsThinkingTokenBudget: false,
+	thinkingTokenBudgetField: undefined,
+	supportsStrictMode: true,
+	supportsOpenAIGrammarTools: false,
+	supportsMidConvoSystemMessages: false,
+	supportsMidConvoToolAdditions: false,
+	cacheControlFormat: "anthropic",
+	sendSessionAffinityHeaders: false,
+	sessionAffinityFormat: "openai",
+	supportsLongCacheRetention: true,
+};
+
+function buildModel(): Model<"openai-completions"> {
+	const { compat: _compat, ...baseModel } = getModel("openai", "gpt-4o-mini");
+	return { ...baseModel, api: "openai-completions", input: ["text", "image"] };
+}
+
+function buildContext(model: Model<"openai-completions">) {
+	const now = Date.now();
+	const assistantMessage: AssistantMessage = {
+		role: "assistant",
+		content: [{ type: "toolCall", id: "tool-1", name: "bash", arguments: { command: "true" } }],
+		api: model.api,
+		provider: model.provider,
+		model: model.id,
+		usage: emptyUsage,
+		stopReason: "toolUse",
+		timestamp: now,
+	};
+	return normalizeContext({
+		messages: [
+			{ role: "user", content: "Run the command", timestamp: now - 1 },
+			assistantMessage,
+			{
+				role: "toolResult",
+				toolCallId: "tool-1",
+				toolName: "bash",
+				content: [{ type: "text", text: "ok" }],
+				isError: false,
+				timestamp: now + 1,
+			},
+			{ role: "user", content: "Thanks", timestamp: now + 2 },
+		],
+	});
+}
+
+describe("requiresNonNullAssistantContent", () => {
+	it("sends null content for tool-call-only assistant messages by default", () => {
+		const model = buildModel();
+		const messages = convertMessages(model, buildContext(model), baseCompat);
+		const assistantMessages = messages.filter((message) => message.role === "assistant");
+		expect(assistantMessages.length).toBe(1);
+		expect(assistantMessages[0].content).toBe(null);
+	});
+
+	it("sends empty string content without inserting an assistant message after tool results", () => {
+		const model = buildModel();
+		const messages = convertMessages(model, buildContext(model), {
+			...baseCompat,
+			requiresNonNullAssistantContent: true,
+		});
+		const roles = messages.map((message) => message.role);
+		expect(roles).toEqual(["user", "assistant", "tool", "user"]);
+		const assistantMessages = messages.filter((message) => message.role === "assistant");
+		expect(assistantMessages.length).toBe(1);
+		expect(assistantMessages[0].content).toBe("");
+	});
+
+	it("still inserts an assistant message when requiresAssistantAfterToolResult is enabled", () => {
+		const model = buildModel();
+		const messages = convertMessages(model, buildContext(model), {
+			...baseCompat,
+			requiresAssistantAfterToolResult: true,
+		});
+		const roles = messages.map((message) => message.role);
+		expect(roles).toEqual(["user", "assistant", "tool", "assistant", "user"]);
+		const assistantMessages = messages.filter((message) => message.role === "assistant");
+		expect(assistantMessages[0].content).toBe("");
+		expect(assistantMessages[1].content).toBe("I have processed the tool results.");
+	});
+});

packages/ai/test/openai-completions-thinking-as-text.test.ts

@@ -31,6 +31,7 @@ const compat = {
 	maxTokensField: "max_completion_tokens",
 	requiresToolResultName: false,
 	requiresAssistantAfterToolResult: false,
+	requiresNonNullAssistantContent: false,
 	requiresThinkingAsText: true,
 	requiresReasoningContentOnAssistantMessages: false,
 	thinkingFormat: "openai",

packages/ai/test/openai-completions-tool-choice.test.ts

@@ -1405,6 +1405,7 @@ describe("openai-completions tool_choice", () => {
 				maxTokensField: "max_completion_tokens",
 				requiresToolResultName: false,
 				requiresAssistantAfterToolResult: false,
+				requiresNonNullAssistantContent: false,
 				requiresThinkingAsText: false,
 				requiresReasoningContentOnAssistantMessages: false,
 				thinkingFormat: "openai",

packages/ai/test/openai-completions-tool-result-images.test.ts

@@ -23,6 +23,7 @@ const compat: Omit<Required<OpenAICompletionsCompat>, "thinkingTokenBudgetField"
 	maxTokensField: "max_completion_tokens",
 	requiresToolResultName: false,
 	requiresAssistantAfterToolResult: false,
+	requiresNonNullAssistantContent: false,
 	requiresThinkingAsText: false,
 	requiresReasoningContentOnAssistantMessages: false,
 	thinkingFormat: "openai",

packages/coding-agent/docs/models-configuration.md

@@ -118,6 +118,7 @@ See [Describe model input and caching](models.md#describe-model-input-and-cachin
 | `maxTokensField` | `"max_completion_tokens" \| "max_tokens"` |  | Which field to use for max tokens. Default: auto-detected from URL. |
 | `requiresToolResultName` | boolean |  | Whether tool results require the name field. Default: auto-detected from URL. |
 | `requiresAssistantAfterToolResult` | boolean |  | Whether a user message after tool results requires an assistant message in between. Default: auto-detected from URL. |
+| `requiresNonNullAssistantContent` | boolean |  | Whether replayed assistant messages with no text (e.g. tool-call-only messages) must send "" instead of null content. Default: false. |
 | `requiresThinkingAsText` | boolean |  | Whether thinking blocks must be converted to text blocks with <thinking> delimiters. Default: auto-detected from URL. |
 | `requiresReasoningContentOnAssistantMessages` | boolean |  | Whether all replayed assistant messages must include an empty reasoning_content field when reasoning is enabled. Default: auto-detected from URL. |
 | `thinkingFormat` | `"openai" \| "openrouter" \| "deepseek" \| "together" \| "baseten" \| "zai" \| "qwen" \| "chat-template" \| "qwen-chat-template" \| "string-thinking" \| "ant-ling"` |  | Format for reasoning or thinking parameters. When omitted, Pi auto-detects the format from the provider URL. "openai" uses reasoning_effort, "openrouter" uses reasoning.effort, "deepseek" uses thinking.type plus reasoning_effort when supported, "together" uses reasoning.enabled plus reasoning_effort when supported, "baseten" uses configurable chat_template_args plus reasoning_effort when supported, "zai" uses thinking.type, "qwen" uses top-level enable_thinking, "qwen-chat-template" uses chat_template_kwargs.enable_thinking and preserve_thinking, "chat-template" uses configurable chat_template_kwargs, "string-thinking" uses top-level thinking, and "ant-ling" uses reasoning.effort only when the mapped effort is non-null. |

packages/coding-agent/schemas/models.schema.json

@@ -552,6 +552,10 @@
           "type": "boolean",
           "description": "Whether a user message after tool results requires an assistant message in between. Default: auto-detected from URL."
         },
+        "requiresNonNullAssistantContent": {
+          "type": "boolean",
+          "description": "Whether replayed assistant messages with no text (e.g. tool-call-only messages) must send \"\" instead of null content. Default: false."
+        },
         "requiresThinkingAsText": {
           "type": "boolean",
           "description": "Whether thinking blocks must be converted to text blocks with <thinking> delimiters. Default: auto-detected from URL."