[vishnuv688]

What & why

Closes #505. Part of #494. Stacked on #509.

Every screenshot in a trace zip was stored as resources/<page>-<timestamp>.jpeg, though WebDriver screenshots and the polling recorder are PNG, so a viewer that takes the content type from the file name served a PNG as image/jpeg. The name now follows the image's own format: .png for PNG, .jpeg for JPEG.

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)
• selenium-devtools-py (Selenium Python adapter)
• backend (server)
• app (UI)
• script (page-injected runtime)
• trace (Trace mode)

Capability matrix

• packages/conformance/src/features.ts updated, and tables regenerated with pnpm docs:capabilities, if this adds or changes user-facing behaviour

Not needed: no per-adapter behaviour changes.

Notes for reviewers

What changed

• imageExtension(base64) in shared names a base64 image's format, from the same magic-byte check as imageMime.
• screenshotResourceName takes the screenshot, so the resource file, the filmstrip frame, the frame-snapshot override and the synthetic resource from Store each action screenshot once in the trace zip #508 all get the same name from one function. When two captures share a timestamp, the snapshot index and the resource writer pick the same one, so a name and its file cannot disagree on format.
• The dense filmstrip had the same bug (every frame was <sha1>.jpeg, though polling mode and CDP with captureFormat: 'png' produce PNG); fixed the same way.

Compatibility

• The reader opens whatever file name an event records, so zips written before this still open, in show-trace and in the hosted player. A test writes a zip, renames the PNG back to .jpeg in both the file and trace.trace as an old zip had it, and checks the reader still returns the image.
• Python needs no change: its adapter sends snapshots to the backend, which writes the zip with trace, so Python traces get the right names automatically.

Testing

• pnpm build, pnpm test (3302 passed) and pnpm lint are green.
• New tests: the extension per format; resource writer and filmstrip agree, including on a shared timestamp; dense frames named by their bytes; in a fully written zip every filmstrip, override and synthetic resource name points at a stored file with a matching mimeType; old .jpeg-named PNG zips still read.

Not verified yet

• A real trace from an example opened in the hosted player and in Playwright's viewer.
• The docs site's wdio/TraceMode.md still says .jpeg; it is updated with the other docs-site changes once trace.webdriver.io is live.

Screenshots / recordings

Not applicable: no UI change.

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