[backryun]

Summary

• declare the tools and tool_choice fields used by both fallback body transformers
• align each native-bypass predicate with the optional targetFormat accepted by its caller
• preserve all web-search and web-fetch transformation behavior

Root cause

Both structural-twin modules constrained their generic request body only as Record<string, unknown>. That permits indexed reads but does not guarantee a named tool_choice property on the generic result when the transformer rewrites it. Their preparation options also allowed an omitted targetFormat, while the bypass predicate receiving the same object declared that field as required.

Diagnostics

Re-measured after rebasing onto release/v3.8.49 at d6c06932e:

• TypeScript 6: 141 → 137
• TypeScript 7: 140 → 136
• full canonicalized error-set diff: 4 removed, 0 added

Validation

• npm run typecheck:core
• npx eslint open-sse/services/webFetchInterception.ts open-sse/services/webSearchFallback.ts
• npm run check:file-size
• web-search, web-fetch, and chat-core interception tests (32/32)
• Prettier run on both touched files
• git diff --check

No new runtime test is needed because this is a type-only contract correction and the existing focused suites cover native bypass, flat/nested tool shapes, tool_choice rewriting, opt-in behavior, and byte-identical no-op paths.

CI note

The new release root includes the pack-artifact-policy.test.ts fixture fix, and that focused test now passes. The unrelated ProviderAccountRoutingCard.tsx:87 hook-dependency ESLint error still reproduces on the base; this PR does not touch that area.