bug(sdk): unguarded JSON.parse on tool-call args kills sendStream (session.ts) #29308

What happened?

packages/sdk/src/session.ts:252-258 calls JSON.parse on model-provided args inside the stream loop with no try/catch:

let args = toolCall.args;
if (typeof args === 'string') {
  args = JSON.parse(args);
}

A single malformed ToolCallRequest.args string throws inside sendStream(), killing the entire for await loop instead of returning a tool error the model can retry. One bad tool call poisons the whole turn.

What did you expect to happen?

Malformed args should produce a functionResponse error part (model-visible) and continue processing remaining events, matching normal tool-error semantics.

Client information

• Repo: google-gemini/gemini-cli @ main 9c1b0a610
• Area: packages/sdk/src/session.ts:252-264
• Platform: source checkout, SDK sendStream path

Login information

N/A — reproducible with a unit test feeding ToolCallRequest with args: "{bad json".

Anything else we need to know?

Fix direction: wrap in try/catch; on failure push error functionResponse and continue; add session.test.ts malformed-args case asserting stream survives + error part emitted. Also consider length cap on string args before parse.