A name the emitted code reads or declares can be one a C# name holds #397

The translation reads some names it never declares, and declares some that a C# name can reach. C# sees neither, so a program C# accepts can mean something else on the web.

Measured

Conformance probes executed on both sides on 2026-09-24 at d4fdd6c, except the last, which is the plain-class emitter's output:

• A local named like a global the lowering calls. int parseInt = 2; return Convert.ToInt32("21") * parseInt; answers 42 in .NET and throws here (parseInt is not a function), because Convert.ToInt32 over text is parseInt('21', 10). var crypto = "xy"; beside Guid.NewGuid() throws the same way (crypto.randomUUID is not a function).
• A name the lowering declares, reached by a C# name. int _sum = 10; xs.Sum(v => v + _sum) over { 1, 2 } answers 23 in .NET and 4 here, with no error: SumStrategy names its accumulator _sum, and the selector's _sum reads it.
• A local named like a binder a LINQ lowering declares, measured on the branch of 🐛 fix: a name the transpiler changes lands on no name its scope holds #399 at ed8681f. var key = 10; read in a key selector, new[] { 1, 2, 3, 4 }.GroupBy(x => x % 2 + key).Count(), throws ReferenceError: Cannot access 'key' before initialization: the reduce arrow of GroupByStrategy declares const key and the selector reads it. int a = -1; read in new[] { 3, 1, 2 }.OrderBy(x => x * a).First() answers 1 where .NET answers 3, with no error: the comparator of OrderByStrategy takes (a, b). Both are common names, and a local FUNCTION called key or a fails the same way (ReferenceError, TypeError).
• A local called props in a constructor with no parameters of its own. The plain-class emitter adds a props parameter, and let props = 5 beside it does not parse.

The free names the lowerings read, from the compiler's source: console (Console.WriteLine), parseInt and parseFloat (Convert over text), crypto (Guid.NewGuid), encodeURIComponent and decodeURIComponent (Uri), undefined, and the constructor's props.

By reading, to measure first: AverageStrategy names its accumulator _sum too, and the two strategies name their other arrows' parameters _x, _a and _b. Copilot's review of #399 names more of them: _idx (List.Remove, which never declares it, #400), and _m, _k, _g, _r, _y, _z in the LINQ lowerings (DistinctStrategy, LinqTableStrategy). A local called undefined or console would shadow the same way. A switch statement's _s did not collide in a constant switch, since that shape does not declare it.

#399 makes a local FUNCTION avoid all of these: a name written with an underscore always takes a $, and the globals are a list that a test derives from the compiler's source. A local keeps its C# spelling, so here it is the emitted code that has to move.

What it wants

The emitted code reading no free name a C# name can reach, and declaring none. A synthesized name is $-prefixed like the IR's own binders ($0, $item), since no C# identifier holds a $. The globals are reached where no local can shadow them (globalThis.parseInt, globalThis.crypto, void 0 for undefined), and the constructor's parameter is $props. Each divergence wants a conformance case that fails before and passes after.