feat(selenium-devtools-py): CDP push-mode screencast and performance capture

[vishnuv688]

What & why

Type of change

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Polish (an improvement to an existing feature)
• Breaking change (existing behavior changes for users)
• Documentation
• Internal (build, CI, dependencies, tooling)

Packages touched

• shared (types and contracts)
• core (framework-agnostic capture/reporting)
• elements (published element/snapshot API — @wdio/elements)
• service (WebdriverIO adapter)
• nightwatch-devtools (Nightwatch adapter)
• selenium-devtools (Selenium adapter)
• backend (server)
• app (UI)
• script (page-injected runtime)
• selenium-devtools-py

Notes for reviewers

Screenshots / recordings

[greptile-apps]

Greptile Summary

The PR adds CDP push-mode screencasting and navigation performance capture to the Python Selenium adapter, while fixing first-selection snapshot replay in the viewer.

• Bounds pushed screencast memory through progressive decimation while preserving the beginning, middle coverage, and final frame.
• Uses a dedicated CDP WebSocket with per-command screenshot fallback.
• Enriches completed navigation command rows with performance and document data.
• Waits for snapshot mode to render before replaying DOM mutations.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
packages/selenium-devtools-py/src/selenium_devtools/screencast.py	Adds synchronized bounded-frame decimation and retains the latest skipped frame during finalization, resolving the previously reported stale video tail.
packages/selenium-devtools-py/src/selenium_devtools/cdp_screencast.py	Implements best-effort push-mode Chrome screencasting over an independently owned CDP connection with frame acknowledgements and cleanup.
packages/selenium-devtools-py/src/selenium_devtools/instrumentation.py	Integrates push-stream lifecycle and post-navigation performance enrichment into per-driver command capture.
packages/selenium-devtools-py/src/selenium_devtools/performance.py	Captures browser navigation and resource timing data and shapes it for replacement command rows.
packages/app/src/components/browser/snapshot.ts	Ensures snapshot mode and its iframe finish rendering before DOM replay begins.
packages/selenium-devtools-py/tests/test_screencast.py	Covers bounded growth, middle-run retention, final-frame preservation, ordering, and idempotent shutdown.

Sequence Diagram

sequenceDiagram
    participant Browser
    participant CDP as Dedicated CDP socket
    participant Recorder as ScreencastRecorder
    participant Finalizer
    Browser->>CDP: screencastFrame
    CDP->>Recorder: add_frame(data)
    CDP->>Browser: screencastFrameAck
    Finalizer->>CDP: stop()
    Finalizer->>Recorder: finalize()
    Recorder->>Recorder: stop() and retain pending tail
    Recorder->>Recorder: encode retained frames

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