Sidecar Telemetry

Every Rust sidecar and the Worker service worker emit through the same land:<tier>:* namespace and stamp $tier so dashboards can pivot without per-Element changes.

Architecture

Type	Path	Wiring
Library	`Element/Common/Source/Telemetry/`	shared. Provides `Capture*::Fn`, `EmitOTLPSpan::Fn`, `Initialize::Fn(Tier)`
Binary	`Element/Air/Source/Binary.rs`	calls `CommonLibrary::Telemetry::Initialize::Fn(Tier::Air)` in `Main`
Binary	`Element/Rest/Source/Main.rs`	calls `Initialize::Fn(Tier::Rest)`
Binary	`Element/Grove/Source/main.rs`	calls `Initialize::Fn(Tier::Grove)` after `Cli::parse`
Binary	`Element/SideCar/Source/main.rs`	sync `main` — spawns short-lived `tokio::Runtime` to call `Initialize::Fn(Tier::SideCar)`
Library	`Element/Echo/Source/Library.rs`	linked into Mountain — emits via `CommonLibrary::Telemetry::CaptureEvent::Fn`, inherits Mountain tier
Library	`Element/Mist/Source/lib.rs`	linked into Mountain and Air — same
Worker	`Element/Worker/Source/Telemetry/Bridge.ts`	TS service worker; auto-loaded from `Worker.ts` install/activate hooks

Tier Identification

Element/Common/Source/Telemetry/Tier.rs:

pub enum Tier {
    Mountain, Air, Echo, Rest, Grove, Mist, SideCar, Common,
}

The Tier is registered once via Initialize::Fn(Tier::X) and read by every Capture*::Fn to stamp $tier / $component automatically.

Mountain — Dual-Init Contract

Mountain runs both its compile-baked plugin (Binary/Build/PostHogPlugin/* for tree-shake guarantee) and Common::Telemetry::Initialize::Fn(Tier::Mountain) so library code linked into Mountain (Echo, Mist) emits through the same client and is tagged $tier=mountain.

Worker

The Worker bridge uses build-baked import.meta.env values and the SW-native fetch API — no posthog-js, no Node https. Loaded lazily inside the __DEV__ branch so astro build with NODE_ENV=production drops it entirely.

What Library Crates Do

Echo / Mist / Common are linked into Mountain (and Air for Mist). They never run as standalone processes, so they never call Initialize::Fn. They emit events using CommonLibrary::Telemetry::CaptureEvent::Fn(name, props) and the resulting events are tagged with the parent process’s tier. Use the name to disambiguate:

// Inside Echo, running in Mountain:
CommonLibrary::Telemetry::CaptureEvent::Fn(
    "land:echo:queue:saturated",
    Some(vec![("queue_depth", "1024")]),
);
// Event arrives in PostHog with $tier=mountain, name=land:echo:*.

Cross-Tier Joining

Every PostHog event carries $trace_id (where the Tier ran an OTLP span). Cocoon’s bridge sets it via Event::SetTraceIdentifier from OTLPBridge.TraceIdentifier(). Common’s EmitOTLPSpan::Fn uses one OTLP_TRACE_ID per process so all spans from one Air / Rest / Grove boot roll into one Jaeger trace.

Profile-Specific Tier Coverage

Some build profiles intentionally skip whole tiers. The Tier Coverage dashboard shows zero counts for those — that is correct behaviour, not a bug:

Profile	Mountain	Cocoon	Sky	Air	Notes
`debug` / `debug-mountain` / `debug-electron`	Yes	Yes	Yes	Yes	Full stack
`debug-cocoon-headless`	Yes	Yes	No	Yes	`Render=false` skips Wind preload + Sky
`debug-mountain-only`	Yes	No	Yes	Yes	`Spawn=false` skips Cocoon
`debug-kernel`	Yes	No	No	Yes	`Spawn=false; Render=false`
`debug-electron-minimal`	Yes	Yes	Yes	Yes	`Skip=true` skips built-in extensions

Mountain’s Binary/Main/Entry.rs always initialises both PostHogPlugin::Initialize and CommonLibrary::Telemetry::Initialize::Fn(Tier::Mountain) regardless of profile.

Adding a New Sidecar

Add Common = { workspace = true } to Element/<New>/Cargo.toml.
Add a variant to Tier::Tier enum.
Call CommonLibrary::Telemetry::Initialize::Fn(Tier::<New>).await from the binary’s main / async entry.
(Optional) Add a tile to the Tier Coverage dashboard pointing at event LIKE 'land:<new>:%'.

Everything else — env propagation from Mountain, OTLP fan-in, $tier tagging, dashboard rollups, prod tree-shake — comes for free.