🟠 Low-Level Shim — Engine-Level Interception

🟠 LOW-LEVEL SHIM — JavaScript engine prototype monkey-patches Tier gate: TierShim=Own | TierShim=Preempt Color: #FF6B35 (Orange) Overhead: <2% in production (sampled)

The Low-Level Shim intercepts VS Code at the JavaScript engine level — before any service, any contribution, any extension has a chance to execute. It operates via prototype-level monkey-patches on VS Code’s internal infrastructure classes.

🟠 Architecture

┌──────────────────────────────────────────────────────────┐
│  🟠 LOW-LEVEL SHIM — 6 Hook Layers                       │
├──────────────────────────────────────────────────────────┤
│  L1: ErrorHandler.onUnexpectedError()  → All errors      │
│  L2: Emitter.prototype.fire()          → All events      │
│  L3: CancellationTokenSource.cancel()  → All aborts      │
│  L4: DisposableStore.add/dispose       → All resources   │
│  L5: setTimeout0 / Async Scheduler     → All async work  │
│  L8: StopWatch / performance.now()     → All timing      │
├──────────────────────────────────────────────────────────┤
│  Dev-only: Promise constructor, Error.stack capture      │
└──────────────────────────────────────────────────────────┘

🟠 How It Works

Each hook is a single prototype-level monkey-patch that wraps VS Code’s internal class methods. When TierShim=Own, the shim activates BEFORE any VS Code code runs. All intercepted data flows through LandDiagnostics to OTLP / PostHog / Mountain dev log.

Example: Emitter.prototype.fire()

const originalFire = Emitter.prototype.fire;
Emitter.prototype.fire = function(event) {
    if (LandSwallowMap.shouldSwallowEmitter(this, event)) {
        LandRedirectBus.routeEmitterEvent(event);
        return; // VS Code listeners never fire
    }
    originalFire.call(this, event);
};

This single 8-line patch covers every event in VS Code — status bar updates, SCM changes, editor state, extension notifications, everything.

🟠 Source Files

🟠 Related Documentation

• Coverage / Telemetry — The high-level application shim (blue)
• Architecture — System architecture overview
• Deep Dive: Mountain — Rust-side intercept infrastructure

⚠️ EXPERIMENTAL — This component operates at the JavaScript engine level. Changes to VS Code’s internal classes may require updates to these hooks. Production overhead: <2% with sampling.