[Maisiqi]

A short navigation deadline could expire after the page had loaded because optional network-idle and render-grace waits consumed the time needed to read the document. This reproduced in the macOS real-Chromium integration test with its existing one-second action budget.

Both optional waits now share at most half of the remaining action budget. Layout and required document observation retain the remainder; the overall deadline and existing maximum wait durations are unchanged. Actual observation timeouts still fail.

This changes settling behavior for future short-budget replays, which can observe a page earlier. It does not edit or regenerate historical attempts, scores, or reports, and does not promise identical results for future reruns. It requires no Web Fetch report changes.

Validation:

• On this branch based directly on main 28534e24, all 64 targeted tests pass, including the unchanged macOS real-Chromium test and six deterministic controls covering fast/idle/streaming networks and successful/timed-out observations.
• The original one-second budget and 1.5-second wall-time assertion are unchanged. The pre-fix executor fails four of the new controls.
• This exact patch previously passed full local make ci and GitHub CI as commit a5da00fd in Make Web Fetch method metadata reusable across versions and cohorts #59. This PR separates it for independent review; its independent GitHub CI run 39735061079 now passes at 608c6e0d, including the complete main test job and Python 3.12/3.13/3.14 Base CLI checks. Optional Claude Review was skipped.

Extracted from #59. No PR is merged by this change.