Report the detected player to GA4

[vpetersson]

The stale-player notice already profiles every viewer to decide whether to warn it, but that judgement was made and thrown away on each load — so the population we're warning, and whether it ever shrinks, was unmeasurable.

This sends the same profile to GA4 as a player_detected event. One detectPlayer() call now feeds both consumers, so the notice and the telemetry can never disagree about what a screen is running.

Client-side for the same reason the notice is: the SSR page cache is keyed by asset version + country + timezone with no user-agent component, so a server-side profile would describe whichever player missed the cache and then be attributed to every hit behind it.

The params

All prefixed player_, since the GA property is shared with the other Screenly-Labs apps:

Param	Example
player_vendor	anthias, brightsign, unknown
player_platform	linux
player_model	XT1144
player_category	signage, browser, bot
player_engine	qtwebengine
player_engine_version	83 (numeric)
player_below_floor	true
player_confidence	high
player_stale	true

Three judgement calls worth review:

• Nulls are sent as "unknown", not omitted — an absent param reads as "(not set)" in GA4, which is indistinguishable from a dimension nobody registered.
• engine_version stays numeric so GA4 will actually aggregate it.
• player_stale is sent despite being derivable from vendor + engine. "Stale" is a judgement this app makes (see the reasoning in stale-player.js) rather than something a report author should re-derive, and it's what makes notice impressions countable against upgrades.

sources is deliberately not sent: page JS can only read the UA and referrer (the X-Requested-With header isn't exposed), so it's near-constant here and would spend a custom dimension on nothing.

Verification

Unit tests cover the param mapping against the same real player UA fixtures the stale-notice suite pins. Beyond that, I drove the built bundle in a browser across four spoofed player UAs — old Anthias, current Anthias, Screenly, BrightSign — with a stubbed gtag so nothing hit the live property:

• exactly one event per load, params correct per player
• player_stale agreed with whether the notice actually mounted
• no-gtag path (dev, or a blocked tag in the field) is a silent no-op with the clock still rendering

Before this reports anything

The params stay invisible in reports until they're registered as custom definitions in the GA4 UI (Admin → Custom definitions) — player_engine_version as a metric, the rest as dimensions.

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