refactor: use Zod schemas for CLI provider JSON parsing

[christso]

Problem

The CLI provider uses as type assertions with manual field validation when parsing JSON output:

const obj = parsed as {
  text?: unknown;
  output_messages?: unknown;
  token_usage?: unknown;
  cost_usd?: unknown;
  duration_ms?: unknown;
};

const costUsd = typeof obj.cost_usd === 'number' && obj.cost_usd >= 0 ? obj.cost_usd : undefined;

This pattern:

• Bypasses TypeScript type safety with as assertions
• Is verbose and repetitive
• Can easily miss validation for a field
• Inconsistent with rest of codebase using Zod

Proposed Solution

Replace with Zod schemas:

const cliOutputSchema = z.object({
  text: z.string().optional(),
  output_messages: z.array(outputMessageSchema).optional(),
  token_usage: tokenUsageSchema.optional(),
  cost_usd: z.number().nonnegative().optional(),
  duration_ms: z.number().nonnegative().optional(),
}).passthrough();

const result = cliOutputSchema.safeParse(parsed);
if (result.success) {
  // result.data is fully typed
}

Files to Update

• packages/core/src/evaluation/providers/cli.ts
  • parseSingleOutput() (~line 329)
  • parseJsonlBatchOutput() (~line 526)

Benefits

• Single source of truth for schema + types
• Better error messages on parse failure
• Reusable schemas (tokenUsage, outputMessages)
• No as assertions
• Consistent with project conventions (Zod in tech stack)

Labels

refactor, good-first-issue