Sidecar Telemetry - Air / Echo / Rest / Grove / Mist / SideCar / Worker

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)`
Binary	`Element/SideCar/Source/Download.rs`	`Tier::SideCar` (vendoring binary)
Library	`Element/Echo/Source/Library.rs`	linked into Mountain - emits via `CommonLibrary::Telemetry::CaptureEvent::Fn`, inherits Mountain’s tier
Library	`Element/Mist/Source/lib.rs`	linked into Mountain & Air - same
Worker	`Element/Worker/Source/Telemetry/Bridge.ts`	TS service worker; auto-loaded from `Worker.ts` install/activate hooks

Cargo.toml additions

# Common (single source of truth for Rust sidecars)
posthog-rs = { workspace = true }

# Each Rust sidecar
Common = { workspace = true }

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/PostHog Plugin/* 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 ends up tagged $tier=mountain).

Worker

The Worker bridge uses build-baked import.meta.env.{Authorize, Beam, OTLPEndpoint, Capture, ...} 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’s correct behaviour, not a bug:

Profile	Mountain	Cocoon	Sky	Air	Notes
`debug` / `debug-mountain` / `debug-electron`	✓	✓	✓	✓	Full stack
`debug-cocoon-headless`	✓	✓	✗	✓	`Render=false` skips Wind preload + Sky telemetry
`debug-mountain-only`	✓	✗	✓	✓	`Spawn=false` skips Cocoon
`debug-kernel`	✓	✗	✗	✓	`Spawn=false; Render=false`
`debug-electron-minimal`	✓	✓	✓	✓	`Skip=true` skips built-in extensions only - telemetry unaffected

Mountain’s Binary/Main/Entry.rs always initialises both PostHogPlugin::Initialize and CommonLibrary::Telemetry::Initialize ::Fn(Tier::Mountain) regardless of profile, so the kernel-only debug binary still produces a full $tier=mountain event stream.

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>:%'

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