feat(selenium-devtools-py): record a dense filmstrip into the trace

[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 dense Selenium Python filmstrips to backend-generated trace archives and completes the previously requested lifecycle and retry fixes.

• Streams screencast frames to the backend in bounded batches.
• Retains frames from finalized and still-live WebDriver sessions.
• Uses an inclusive timestamp watermark to retry only the unsent tail without losing equal-timestamp frames.
• Adds backend accumulation/export support and focused lifecycle, batching, and retry tests.

Confidence Score: 5/5

The PR appears safe to merge because the previously reported filmstrip lifecycle and retry failures are fixed.

No blocking failure remains.

Important Files Changed

Filename	Overview
packages/selenium-devtools-py/src/selenium_devtools/init.py	Enables filmstrip capture and coordinates frame streaming, retry watermarks, and run-state reset; the previously reported retry boundary issues are addressed.
packages/selenium-devtools-py/src/selenium_devtools/instrumentation.py	Collects finalized and live recorder buffers and preserves live frames across uninstall before session state is cleared.
packages/selenium-devtools-py/src/selenium_devtools/trace_export.py	Streams frame batches defensively without allowing optional filmstrip failures to break the Selenium run.
packages/backend/src/baselineStore.ts	Accumulates the new screencast frame stream for subsequent server-side trace export.
packages/backend/src/trace-export.ts	Passes non-empty dense filmstrip data into trace generation while preserving sparse fallback behavior.
packages/selenium-devtools-py/tests/test_filmstrip.py	Covers batching, live and finalized frame retention, opt-out behavior, retry boundaries, equal timestamps, decimation, and uninstall ordering.

Sequence Diagram

sequenceDiagram
    participant R as Selenium recorder
    participant P as Python adapter
    participant B as Backend
    participant T as Trace exporter
    R->>P: Buffered screencast frames
    P->>B: screencastFrames batches
    B->>B: Accumulate frames in active run
    P->>B: traceExport request
    B->>T: Export active run with dense filmstrip
    T-->>B: trace.zip
    B-->>P: Export result
    Note over P,B: Failed exports retry from the inclusive timestamp watermark

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