Fix bounded adaptive screenshot publication

[chubes4]

Summary

• capture unresolved-navigation screenshots into memory during the bounded attempt
• publish screenshot.png only after liveness succeeds
• prevent timed-out Playwright work from materializing an unreferenced artifact later
• accept both documented outcomes in the regression: captured screenshot or typed unavailability

Fixes #2419.

Root Cause

withBrowserCommandLiveness can bound waiting but cannot cancel Playwright’s pending page.screenshot({ path }). After timeout, that operation could still write screenshot.png, producing either a missing-file test failure or a late orphan file absent from the artifact summary and manifest.

The bounded adaptive path now requests Playwright’s screenshot buffer without a destination path. Only a successful bounded result is written through BrowserArtifactSession; late completion after timeout has no filesystem side effect. Normal settled capture remains unchanged.

Verification

• 10 consecutive runs of npx tsx --test tests/browser-actions-navigation-capture.browser.test.ts
• npx tsx --test tests/browser-actions-navigation-capture.browser.test.ts tests/browser-adaptive-exploration.test.ts (31 passed)
• npm run build
• git diff --check

This was discovered in the v0.26.0 Homeboy release preflight. The failed release rolled back cleanly and created no tag.

AI Assistance

OpenAI GPT-5.6 Sol through OpenCode reproduced both sides of the late-write race, traced the uncancelled Playwright promise through the artifact writer, implemented publish-after-liveness buffering, and ran repeated browser verification under Chris Huber’s direction.