fix(ai): pruned optional empty tool params

Treat empty strings on optional tool arguments as omitted before schema validation so MCP calls do not fail pattern or type checks for model-filled placeholders.

Fixes #2981

packages/ai/CHANGELOG.md

@@ -42,6 +42,7 @@
 - Fixed OpenRouter Responses requests tagging the streamed assistant message with a hardcoded `openai-responses` API instead of the runtime `model.api`, which silently disabled native-history replay (`buildResponsesInput`) and cross-model tool-call item-id stripping on subsequent OpenRouter turns. The message now carries `model.api` (matching the Chat Completions path).
 - Fixed OpenAI-family streaming leaking a pre-retry `errorMessage` onto a successful turn: the OpenRouter Anthropic compiled-grammar strict-tool fallback set `errorMessage` before retrying with strict tools disabled and never cleared it on success, and the Chat Completions success path could carry an `errorMessage` from an internally-retried attempt — both made a successful turn read as errored in agent state and telemetry. The Responses fallback no longer assigns `errorMessage`, and the Completions success path clears it before emitting the terminal `done` event.
 - Fixed Codex stream-error `.code` resolution to use the same nested-first precedence (`error.code` → `error.type` → top-level `code`) as `isRetryableCodexFailureEvent` and the formatted message. Previously the error factory resolved top-level-first, so a failure event carrying both a top-level and a differing nested error code surfaced a `.code` that could disagree with its own `retryable` flag and message text.
+- Fixed MCP tool argument validation to drop optional empty-string parameters before schema validation, matching the existing optional null handling and avoiding pattern/type failures for omitted model-filled fields. ([#2981](https://github.com/can1357/oh-my-pi/issues/2981))
 
 ## [16.0.5] - 2026-06-17
 

packages/ai/src/utils/validation.ts

@@ -764,10 +764,11 @@ function normalizeOptionalNullsForSchema(
 		if (!(key in nextValue)) continue;
 		const currentValue = nextValue[key];
 		const isNullish = currentValue === null || currentValue === "null";
+		const isEmptyString = currentValue === "";
 
-		// Strip null and the string "null" from optional fields.
-		// The LLM sometimes outputs string "null" to mean "no value".
-		if (isNullish && !required.has(key)) {
+		// Strip null, string "null", and empty strings from optional fields.
+		// LLMs sometimes output these placeholders to mean "no value".
+		if ((isNullish || isEmptyString) && !required.has(key)) {
 			if (!changed) {
 				nextValue = { ...nextValue };
 				changed = true;
@@ -1281,7 +1282,8 @@ function truncateArgsForError(value: unknown): unknown {
 /**
  * Validates tool call arguments against the tool's schema (Zod or plain JSON
  * Schema). Applies LLM-quirk coercions (numeric strings, JSON-string
- * containers, null-for-optional, null-for-default) before declaring failure.
+ * containers, null/empty-string-for-optional, null-for-default) before
+ * declaring failure.
  *
  * @throws Error with a formatted message when validation cannot be reconciled.
  */
@@ -1290,9 +1292,9 @@ export function validateToolArguments(tool: Tool, toolCall: ToolCall): ToolCall[
 	const ctx = getValidationContext(tool);
 	const { json } = ctx;
 
-	// Always normalize first — strip null and string "null" from optional
-	// fields and substitute defaults. Handles LLM outputting string "null"
-	// to mean "no value" even when validation would otherwise pass.
+	// Always normalize first — strip null, string "null", and empty strings
+	// from optional fields and substitute defaults. Handles LLM outputting
+	// placeholders for "no value" even when validation would otherwise pass.
 	let normalizedArgs: unknown = originalArgs;
 	let changed = false;
 	const initialNormalization = normalizeOptionalNullsForSchema(json, normalizedArgs);

packages/ai/test/tool-argument-coercion.test.ts

@@ -898,6 +898,32 @@ describe("Tool argument coercion", () => {
 		expect(result).toEqual({ requiredText: "ok" });
 	});
 
+	it("strips empty strings from optional properties before schema validation", () => {
+		const tool: Tool = {
+			name: "mcp-like",
+			description: "",
+			parameters: {
+				type: "object",
+				properties: {
+					namespace: { type: "string" },
+					fieldSelector: { type: "string", pattern: "^.+$" },
+					limit: { type: "number" },
+				},
+				required: ["namespace"],
+				additionalProperties: false,
+			},
+		};
+
+		const result = validateToolArguments(tool, {
+			type: "toolCall",
+			id: "call-empty-optionals",
+			name: "mcp-like",
+			arguments: { namespace: "kube-system", fieldSelector: "", limit: "" },
+		});
+
+		expect(result).toEqual({ namespace: "kube-system" });
+	});
+
 	it("drops null optional properties nested in array objects", () => {
 		const tool: Tool = {
 			name: "t12",
@@ -924,7 +950,7 @@ describe("Tool argument coercion", () => {
 		expect(result).toEqual({ edits: [{ target: "a", end: "e" }] });
 	});
 
-	it("drops null optional properties in anyOf object branches", () => {
+	it("drops null and empty-string optional properties in anyOf object branches", () => {
 		const opSchema = z.union([
 			z.object({
 				op: z.literal("add_task"),
@@ -972,7 +998,6 @@ describe("Tool argument coercion", () => {
 					op: "update",
 					id: "task-1",
 					status: "completed",
-					notes: "",
 				},
 			],
 		});