Fix optional Zod fields in native structured output

[EricLiu2795]

Summary

Fixes #335.

The shared structured-output path could fail before making a provider request when native json-schema mode was selected for a Zod schema containing optional object properties such as:

z.object({
  required: z.string(),
  optional: z.string().optional(),
})

The adapter now detects this native-schema incompatibility before invocation and uses the existing strict-JSON prompt plus local Zod validation fallback. Required schemas continue to use native JSON Schema, and ordinary provider failures are not rerouted.

The current Founder Weekly Review recommendation schema is covered without changing the FWR schema itself.

Validation

• Shared LLM surface: 6 suites, 111 tests passed
• Focused structured-output regression: 8 tests passed
• Current-main FWR generation tests: 30 tests passed
• Affected-package typechecks: PASS
• Changed-file lint: PASS
• Formatting: PASS
• git diff --check: PASS
• No live provider calls were made; local mock endpoints proved the path proceeds beyond schema preparation.

No migrations, provider-specific routing, retry/outbox logic, or unrelated infrastructure were changed.

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Project	Deployment	Actions	Updated (UTC)
launch-stack	Error		Aug 16, 2026 3:51pm
pdr-ai-v2	Error		Aug 16, 2026 3:51pm