Browser callback materialization contract expects stale response shape

[chubes4]

Problem

The repository's broad check gate fails in an unchanged browser callback contract test because runtime response diagnostics now include fields that the exact expected object omits.

Reproduction

npm run test:browser-callback-materialization-contracts

Observed diff at tests/browser-callback-materialization-contracts.test.ts:245:

contentLength: '2' and bodyRewritten: false are present in the actual response record but absent from the expected object.

Impact

npm run check stops in test:generic-primitives, preventing unrelated changes from reaching the rest of the smoke gate.

Expected

Align the fixture expectation with the current response contract, or remove the fields from runtime output if they are unintended. This was reproduced on origin/main-based commit 52cf495f while working on unrelated temp retention code; no browser callback source or test files were changed.

[chubes4]

Resolved by merged PR #2346. The diagnostics are intentional typed fields; current main passes the browser callback contract test, generic primitives, build, and the full 101-command check gate. Closing this older duplicate without creating redundant code churn.