- ambientUndefVarRootOf walks calls, `new`, optional chains, assertions, instantiation expressions, and tagged templates, and accepts `declare function` and trap-binding roots: Node erases the declaration, so the root read IS the crash — lowerCall, member reads, assignments, and variable declarations lower the whole statement to the catchable ReferenceError, arguments never evaluate, and the never-initialized binding registers as a trap whose references can never run
- never-read unmappable bindings with value-only initializers and writes emit nothing: Node builds the value and drops it, so `var xs2: typeof Array;` and the write-only `var f2: { <T, U>(x: T, y: U): T }` compile instead of fencing on a type the program never consumes
- null!/as-any bindings whose types keep generic signatures (or intern empty record shapes) register no storage; generic-method calls and member reads through them compile to Node's exact TypeError, nullish-to-nullish flows to nothing, heritage-clause uses decline the family so mixin resolution keeps its fence, and checked-dynamic (`any`) bindings keep their dyn story untouched
- assertion-shaped generic arrows (`< <T>(x: T) => T >((x) => x)`) register like annotated bindings and monomorphize per call; stdlib generic members (Promise.then, Object.defineProperty) take the SC2020 lib fence, and Function.prototype.apply/call/bind on compiled function values name the direct-call spelling
- diagnostics fixtures that used `declare` to conjure unconstructible values now conjure them by cast so each fence family keeps its pin; snapshots re-recorded, the deferred checker-panic diagnostic now flushes at its first reference as designed
- Number pairs take a new scr_num_same_value runtime primitive (NaN equals NaN, +0 differs from -0 — the two divergences from ===); strings, booleans, unit literals, and every reference kind (arrays, records, class instances with hierarchy widening, functions, class values, Maps/Sets, symbols, typed arrays, promises) ride exactly the strict-equality machinery, whose answers SameValue shares.
- Union operands lower through unionEq, which grows a sameValue flag: the f64 arm's payload compare upgrades to SameValue (a separate interned C helper per union; the LLVM lane calls the runtime primitive inline), every other arm is shared between the two semantics.
- Statically disjoint kind pairs answer the constant false with the operands still evaluated for their effects (Object.is is (any, any) — tsc admits every pair); dyn/jsval operands and partially-overlapping unions fence by name with strict equality's validate/narrow-first stance.
- Differential fixture 2561 pins the NaN/±0 edges, mixed-kind calls with effect counting, reference identity across kinds, and union payloads (including NaN/±0 inside a union and union-vs-plain wraps) byte-identically vs Node on both backends; stdlib-fence pins the named fences.
- Found pre-existing (reproduced at the base commit): the C backend SIGSEGVs on console.log(asBase === d, asBase === new Base()) — an upcast identity compare plus a constructing compare in one call; the fixture avoids the shape and the bug is reported for a follow-up lane.
- The performance global routes through the perf_hooks lowering in all spellings
- Response declares its implemented headers/arrayBuffer/bytes surface
- Math.max and Math.min lower at any arity
- Copy-installed workspace members classify like symlinked ones
Chris Tate