fix(mastra): propagate Gemini thought_signature (providerMetadata) through the AG-UI stack

[antanj]

Problem

Gemini 2.5+ models attach a thought_signature to tool calls via providerMetadata.
During a client-side tool round-trip, this metadata was silently dropped at every layer
of the AG-UI stack, causing Gemini to reject the follow-up request with:

AI_APICallError: Function call is missing a thought_signature
Fixes #1245.

Changes

@ag-ui/core

• Added providerMetadata?: Record<string, Record<string, any>> to ToolCallSchema (types.ts)
• Added the same field to ToolCallStartEventSchema (events.ts)

@ag-ui/client

• apply/default.ts: destructure providerMetadata from TOOL_CALL_START events and
  conditionally include it on the ToolCall object stored in messages

@ag-ui/mastra

• mastra.ts: forward providerMetadata from both the local agent (fullStream) and
  remote agent (processDataStream) tool-call chunks into the ToolCallStartEvent
• utils.ts: restore providerMetadata onto tool-call parts when converting
  AssistantMessage.toolCalls back to Mastra CoreMessage format, so Gemini
  receives the signature on the next request

Tests

• 2 new tests in message-conversion.test.ts: verify providerMetadata is preserved
  (or cleanly absent) when converting AG-UI messages to Mastra format

• 2 new tests in default.tool-calls.test.ts: verify TOOL_CALL_START → ToolCall
  passthrough in the client apply layer

  [Bug]: Gemini 2.5 or 3 tool calls fail with missing thought_signature in @ag-ui/mastra roundtrip (frontend/client tool flows) #1245

[vercel]

@antanj is attempting to deploy a commit to the CopilotKit Team on Vercel.

A member of the Team first needs to authorize it.

[jpr5]

Code review

Found 1 issue:

1. Schema type mismatch on providerMetadata between ToolCallStartEventSchema and ToolCallSchema. The event schema uses the flat z.record(z.string(), z.any()) (Record<string, any>) while the ToolCall schema uses the nested z.record(z.string(), z.record(z.string(), z.any())) (Record<string, Record<string, any>>). These describe the same field but with different shapes -- the event schema is strictly looser than the type it feeds into. The fix is to make the event schema match the ToolCall schema.

ag-ui/sdks/typescript/packages/core/src/events.ts

Lines 125 to 127 in 85f4a14

	parentMessageId: z.string().optional(),
	});

vs.

ag-ui/sdks/typescript/packages/core/src/types.ts

Lines 12 to 14 in 85f4a14

	encryptedValue: z.string().optional(),
	});

[antanj]

Code review

Found 1 issue:

1. Schema type mismatch on providerMetadata between ToolCallStartEventSchema and ToolCallSchema. The event schema uses the flat z.record(z.string(), z.any()) (Record<string, any>) while the ToolCall schema uses the nested z.record(z.string(), z.record(z.string(), z.any())) (Record<string, Record<string, any>>). These describe the same field but with different shapes -- the event schema is strictly looser than the type it feeds into. The fix is to make the event schema match the ToolCall schema.

ag-ui/sdks/typescript/packages/core/src/events.ts

Lines 125 to 127 in 85f4a14

	parentMessageId: z.string().optional(),
	});

vs.

ag-ui/sdks/typescript/packages/core/src/types.ts

Lines 12 to 14 in 85f4a14

	encryptedValue: z.string().optional(),
	});

Thanks, resolved.

[jpr5]

Code review (re-review after schema fix)

Schema mismatch is resolved. Found 2 issues:

1. Python SDK not updated -- ToolCall and ToolCallStartEvent in sdks/python/ag_ui/core/ are missing provider_metadata. The repo has a strong sync discipline between Python and TypeScript SDKs (the 5 most recent commits to Python SDK types are all "align with TypeScript SDK" fixes, and commit bd5f93f updated both simultaneously for the name field). Python agents/clients will silently drop providerMetadata, breaking the Gemini thought_signature use case for Python consumers.

ag-ui/sdks/typescript/packages/core/src/types.ts

Lines 11 to 14 in 670c7e0

	function: FunctionCallSchema,
	encryptedValue: z.string().optional(),
	providerMetadata: z.record(z.string(), z.record(z.string(), z.any())).optional(),
	});

ag-ui/sdks/python/ag_ui/core/types.py

Lines 30 to 37 in 670c7e0

	class ToolCall(ConfiguredBaseModel):
	"""
	A tool call, modelled after OpenAI tool calls.
	"""
	id: str
	type: Literal["function"] = "function" # pyright: ignore[reportIncompatibleVariableOverride]
	function: FunctionCall
	encrypted_value: Optional[str] = None

2. Protobuf schema not updated -- events.proto and types.proto are missing provider_metadata. The same commit bd5f93f updated proto and TypeScript simultaneously. Agents using the proto/binary transport path will silently lose providerMetadata during serialization.

ag-ui/sdks/typescript/packages/proto/src/proto/events.proto

Lines 1 to 10 in 670c7e0

	syntax = "proto3";
	package ag_ui;
	import "google/protobuf/struct.proto";
	import "patch.proto";
	import "types.proto";
	enum EventType {
	TEXT_MESSAGE_START = 0;

[antanj]

Code review (re-review after schema fix)

Schema mismatch is resolved. Found 2 issues:

1. Python SDK not updated -- ToolCall and ToolCallStartEvent in sdks/python/ag_ui/core/ are missing provider_metadata. The repo has a strong sync discipline between Python and TypeScript SDKs (the 5 most recent commits to Python SDK types are all "align with TypeScript SDK" fixes, and commit bd5f93f updated both simultaneously for the name field). Python agents/clients will silently drop providerMetadata, breaking the Gemini thought_signature use case for Python consumers.

ag-ui/sdks/typescript/packages/core/src/types.ts

Lines 11 to 14 in 670c7e0

	function: FunctionCallSchema,
	encryptedValue: z.string().optional(),
	providerMetadata: z.record(z.string(), z.record(z.string(), z.any())).optional(),
	});

ag-ui/sdks/python/ag_ui/core/types.py

Lines 30 to 37 in 670c7e0

	class ToolCall(ConfiguredBaseModel):
	"""
	A tool call, modelled after OpenAI tool calls.
	"""
	id: str
	type: Literal["function"] = "function" # pyright: ignore[reportIncompatibleVariableOverride]
	function: FunctionCall
	encrypted_value: Optional[str] = None

2. Protobuf schema not updated -- events.proto and types.proto are missing provider_metadata. The same commit bd5f93f updated proto and TypeScript simultaneously. Agents using the proto/binary transport path will silently lose providerMetadata during serialization.

ag-ui/sdks/typescript/packages/proto/src/proto/events.proto

Lines 1 to 10 in 670c7e0

	syntax = "proto3";
	package ag_ui;
	import "google/protobuf/struct.proto";
	import "patch.proto";
	import "types.proto";
	enum EventType {
	TEXT_MESSAGE_START = 0;

Resolved.