TypeScript checker parity: eliminate the remaining 30 failures

Parent: #67

Scope

Make ts_checker fully green by porting the remaining TypeScript semantics and exact diagnostic behavior. Do not weaken assertions or encode fixture-specific outcomes.

Current verified state

After fixing distributive-conditional union member ownership:

• 2,976 / 3,006 pass
• 30 fail
• 0 crash (down from 2 crashes)

The crash fix copies union member IDs before recursive conditional evaluation so interner reallocations cannot invalidate a borrowed slice.

Remaining failure clusters

• Enum/member literal assignment compatibility.
• Global-script this indexed access diagnostics.
• Generic defaults, conditional distribution, NonNullable, mapped and template types.
• Variadic tuple inference and callback arity.
• Overload diagnostic anchoring and CheckJS/JSDoc arity.
• Accessor read/write and spread typing.
• Alias/generic-instance diagnostic rendering.
• Recursive type depth/circular mapped diagnostics.

Completion gate

• ./pantry/.bin/zig build test -Dfilter=ts_checker --summary failures reports 3,006 / 3,006.
• No crash, timeout, or skipped parity assertion replaces a failure.
• Each semantic cluster lands in a focused conventional commit with regression coverage.

Checker parity update pushed in bc8cc74bf (fix(ts-checker): validate generic conditional returns).

• Added branch-level return validation for conditional expressions targeting builtin Object.
• Unconstrained generic branches now emit TS2322 at each branch expression; constrained branches are accepted through the existing relation engine.
• Added the two missing line-25 diagnostics in bestCommonTypeOfConditionalExpressions.
• Targeted exact pair: 1/2 -> 2/2 (+1 complete fixture).
• Projected aggregate: 4,874/5,907 (82.51%), with 1,033 remaining pending the next complete survey.
• Checker suite: 3,029/3,029 passing.

Issue remains open.

Checker parity update pushed in d3efb9cbb (fix(ts-checker): resolve Document from DOM lib).

• Added DOM-gated builtin type resolution for Document in virtual declaration modules.
• @lib: es2020,dom now resolves Document in .d.html.ts; explicit lib lists without dom still emit the missing-name diagnostic.
• Exact pair: 0/2 -> 2/2.
• Newly exact-passing fixtures: declarationFileForHtmlImport, declarationFileForHtmlFileWithinDeclarationFile.
• Projected aggregate: 4,876/5,907 (82.55%), with 1,031 remaining pending the next complete survey.
• Checker suite: 3,030/3,030 passing.

Issue remains open.

Checker parity update pushed in b774a24d5 (fix(ts-checker): infer overloaded class constructors).

• Aligned new applicability with ordinary-call and super inference by instantiating every construct signature from arguments before checking it.
• Class type parameters now infer without requiring a separate generic-signature side-table record.
• Newly exact-passing fixtures: constructSignaturesWithIdenticalOverloads, constructSignaturesWithOverloads, constructSignaturesWithOverloads2.
• Exact overload filter: 1/4 -> 4/4 (+3 complete fixtures).
• Projected aggregate: 4,879/5,907 (82.60%), with 1,028 remaining pending the next complete survey.
• Checker suite: 3,031/3,031 passing.

Issue remains open.

Checker parity update pushed in cfefae033 (fix(ts-checker): constrain template infer placeholders).

• Bare ${infer T} placeholders inside template-literal patterns now inherit TypeScript implicit string constraint.
• Explicit ${infer T extends X} constraints still take precedence; non-template infer declarations are unchanged.
• Removed four spurious TS2344 diagnostics from templateLiteralTypes1.
• Exact fixture result: 0/1 -> 1/1.
• Projected aggregate: 4,880/5,907 (82.62%), with 1,027 remaining pending the next complete survey.
• Checker suite: 3,032/3,032 passing.

Issue remains open.

Follow-up measurement for cfefae033: the same template-infer constraint fix also flips templateLiteralTypes3 to exact-pass by removing the spurious recursive Parts<Tail> TS2345.

• Additional verified fixture: templateLiteralTypes3 (0/1 -> 1/1).
• Total measured movement for cfefae033: +2 complete fixtures, not only the initially targeted +1.
• Corrected projected aggregate: 4,881/5,907 (82.63%), with 1,026 remaining.
• No code or history rewrite was needed; this is a broader verification of the pushed semantic rule.

Pushed a284a1abd (fix(ts-checker): preserve nonnullable string intersections).

This ports two connected TypeScript semantics:

• {} remains the empty-object/non-nullish type, so string & {} and template-string intersections stay inhabitable; lowercase object & string still reduces to never.
• A recognized NonNullable<X> -> X assignment updates X's flow type without relaxing unrelated generic-intersection assignment narrowing.

Measured exact flips:

• templateLiteralTypes2: 0/1 -> 1/1
• conditionalTypes1: 0/1 -> 1/1

Projected exact aggregate: 4,883/5,907 (82.66%), up from 4,881; 1,024 remain. The complete focused checker suite is green at 3,032/3,032. The 101-200 exact window is now projected at 98/100, with only the two this-type fixtures left.

Commit: https://github.com/home-lang/home/commit/a284a1abdd68be3c7fb6903a048d7eafbafecab1

Pushed 98e703f00 (fix(ts-checker): scope mapped key parameters).

This ports declaration-scoped mapped-key identity into Home: each mapped [K in ...] declaration now receives a stable fresh type-parameter ID, preventing same-named keys in earlier aliases from leaking substitutions into later reverse-mapped inference. It also avoids running the stale post-success nested diagnostic snapshot for the callable-or-Computed<T> accessor union shape, while a companion regression confirms genuinely incompatible accessor calls still report TS2322.

Measured parity impact:

• thisTypeInObjectLiterals2: exact 0/1 -> 1/1 (+1 fixture)
• projected aggregate: 4883/5907 -> 4884/5907 (82.68%), 1023 remaining
• checker coverage: 3032 -> 3034 tests; full checker suite 3034/3034 green
• post-rebase exact rerun: 1/1 green

No user-owned corpus runner changes were included in the commit.

Pushed 32c45e414 (fix(ts-checker): preserve class this identity).

• caches one polymorphic this type per class declaration so nested arrows, annotations, and receivers share identity
• routes polymorphic this call parameters through ordinary assignability instead of the unconstrained-generic shortcut
• exact thisTypeInClasses: 0/1 -> 1/1 (+1)
• exact 101-200 window: 99/100 -> 100/100 for this chunk (98/100 -> 100/100 across the paired mapped/class this fixes)
• projected aggregate: 4,884 -> 4,885 / 5,907 (82.70%), 1,022 remaining
• checker suite: 3,034 -> 3,035 tests, passing 3,035/3,035

Commit: https://github.com/home-lang/home/commit/32c45e41481f91e051742c41d0ea9ba8b2fc2553

Pushed ae52652ab (fix(ts-checker): preserve variadic mapped tuple tails).

• preserves trailing generic tuple operands separately from array rest elements through homomorphic mapping and substitution
• reverse-infers mapped array-literal tails as tuple slices
• applies existing mutable/readonly/constrained variadic relations when assignments involve bare type parameters
• exact variadicTuples1: 0/1 -> 1/1 (+1)
• diagnostic correction: 4 missing TS2322s added, 1 spurious TS2322 removed
• exact 201-300 window: 99/100 -> 100/100
• projected aggregate: 4,885 -> 4,886 / 5,907 (82.72%), 1,021 remaining
• checker suite: 3,035 -> 3,037 tests, passing 3,037/3,037
• conformance harness: 1,368/1,368, baseline-aware 586/586

Commit: https://github.com/home-lang/home/commit/ae52652abbd9a78750ad0714c7d6e40e1acb20c0

Pushed abb985e6c (fix(ts-checker): retain optionality in object literal relations).

• Preserves source-member optionality in the object-literal assignability fast path, so optional spread properties cannot satisfy required targets.
• Adds a strict-null regression for two optional spreads while retaining required-then-optional overwrite behavior.
• Exact parity: objectSpreadNegative 0/1 -> 1/1; window 301-400 87/100 -> 88/100.
• Projected aggregate: 4886 -> 4887/5907 (82.73%), 1020 remaining.
• Verification: ts_checker 3038/3038; ts_conformance package gate; exact 301-400 survey.

Pushed b5d3b59ce (fix(ts-checker): render optional parameter undefined types).

• Preserves the implicit | undefined constituent in optional-parameter diagnostic text across ordinary, nested, method, and construct callable renderers.
• Adds an interface-member assignment regression matching the upstream diagnostic path.
• Exact parity: assignmentCompatWithCallSignaturesWithOptionalParameters 0/1 -> 1/1; all 17 TS2322 headlines now match; window 301-400 88/100 -> 89/100.
• Projected aggregate: 4887 -> 4888/5907 (82.75%), 1019 remaining.
• Verification: ts_checker 3039/3039; ts_conformance package gate; exact 301-400 survey.

Pushed ecca733b4 (fix(ts-checker): nest type parameter instantiation diagnostics).

• Emits primary TS2322 for sibling type-parameter mismatches, with TS5075/TS5082 wording in the child chain.
• Keeps standalone TS5075/TS5082 for concrete sources and restores TS2208 related hints for unconstrained source parameters.
• Exact parity: typeParameterAssignability, typeParameterAssignability3, and unionTypesAssignability each 0/1 -> 1/1; window 301-400 89/100 -> 92/100.
• Projected aggregate: 4888 -> 4891/5907 (82.80%), 1016 remaining.
• Verification: ts_checker 3040/3040; ts_conformance package gate; exact 301-400 survey.

Pushed deecad45b (fix(ts-checker): preserve numeric property diagnostic spelling).

This ports TypeScript's distinction between canonical property identity and declaration spelling into TS2741 diagnostics: inferred object members retain their declaration nodes, quoted numeric keys remain quoted in structural shapes, numeric missing-property names preserve source spellings such as 1.0 and 1., compact optional members omit implicit | undefined, and namespace-scoped declaration names render in the expected bare form. Tuple and alias display paths remain protected.

Parity movement:

• assignmentCompatWithObjectMembersStringNumericNames: 0/1 -> 1/1
• exact fixtures 301-400: 92/100 -> 93/100
• aggregate exact parity: 4,891/5,907 -> 4,892/5,907 (82.82%)
• remaining exact fixtures: 1,015

Verification:

• checker: 3,041/3,041
• conformance package gate: passed
• exact 301-400 survey: 93/100

One focused checker regression now covers quoted numeric keys, original decimal spellings, compact optional shapes, namespace-local type names, and the legacy tuple/alias safeguards.

Pushed 7c6b4f523 (fix(ts-checker): preserve mutable object assignment slots).

This ports two related assignment-compatibility details: an existing flow-map entry only counts as an active narrow when it actually differs from the declared mutable slot, so a valid Base <- Derived write no longer changes later reads of that slot to Derived; and class instances nested in anonymous object diagnostics render by their leaf class name while retaining generic arguments.

Parity movement:

• assignmentCompatWithObjectMembers4: 0/1 -> 1/1
• exact fixtures 301-400: 93/100 -> 94/100
• aggregate exact parity: 4,892/5,907 -> 4,893/5,907 (82.83%)
• remaining exact fixtures: 1,014

Verification:

• checker: 3,042/3,042
• conformance package gate: passed
• exact 301-400 survey: 94/100

The focused regression verifies the valid subtype write, the invalid reverse write, the preserved mutable slot type, and bare nested class names in TS2322 prose.

Pushed 7bec2cf56 (fix(ts-checker): relate discriminated tuple conditionals).

• Ported equality OR-chain narrowing and flow-aware fixed tuple relation for conditional array branches.
• Routed namespace conditional initializers through contextual declaration checking.
• Added the required common-discriminant undefined diagnostic while preserving optional discriminants.
• Added focused GH39357 and GH12052 checker regressions.

Parity impact: assignmentCompatWithDiscriminatedUnion flips 0/1 -> 1/1; exact fixtures 301-400 improve 94/100 -> 95/100; canonical aggregate exact parity improves 4,893/5,907 -> 4,894/5,907 (82.85%), leaving 1,013.

Verification: ts_checker 3,044/3,044, ts_conformance package gate, exact 301-400 95/100, and baseline/current full-corpus failure-name comparison found no fixture-outcome regressions.

Pushed bca3f94ee (fix(ts-checker): reject void generic returns).

The generic alpha relater now applies the checker-owned type-parameter mismatch guard to substituted return types before the permissive low-level relation. This preserves alpha-equivalent generic returns while rejecting callable and construct signatures whose void return cannot satisfy an unconstrained type-parameter return.

Parity impact: assignmentCompatWithCallSignatures6 and assignmentCompatWithConstructSignatures5 each flip 0/1 -> 1/1; exact fixtures 301-400 improve 95/100 -> 97/100; canonical aggregate exact parity improves 4,894/5,907 -> 4,896/5,907 (82.88%), leaving 1,011.

Verification: ts_checker 3,045/3,045, ts_conformance package gate, exact 301-400 97/100.

Pushed e97dadc41 (fix(ts-checker): preserve enclosing construct generics).

This ports the construct-signature inference boundary more faithfully: only type parameters owned by a construct signature are inferred from new arguments, while type parameters captured from an enclosing generic scope remain fixed. Nullish argument checking now distinguishes unconstrained captured parameters, constrained captured parameters under legacy non-strict null behavior, and signature-owned generics, and TS2345 carries the arbitrary-instantiation child diagnostic. The chunk also makes the GH12052 required-discriminant undefined diagnostic structural, removing its dependence on leaked strict-null relation state.

Exact parity impact:

• genericCallWithFunctionTypedArguments2: 0/1 -> 1/1
• genericCallWithConstructorTypedArguments5: 0/1 -> 1/1
• exact fixtures 401-500: 68/100 -> 70/100
• canonical aggregate: 4,896/5,907 -> 4,898/5,907 (82.92%), 1,009 remaining
• implementation: 36 insertions, 12 deletions in packages/ts_checker/src/check.zig

Verification:

• ts_checker: 3,046/3,046
• ts_conformance package gate: green; baseline-aware survey 586/586
• named exact fixtures: 2/2
• finalized exact 401-500 survey: 70/100; the other 30 failure names are unchanged.

Pushed parity chunk 7d7121d89 (fix(ts-checker): anchor override diagnostics to fields).

This ports TypeScript's field-level diagnostic anchoring for TS2416: override mismatches now point at the written property key instead of the full declaration. That preserves the derived-field location while matching TypeScript's span and stable ordering when TS2416 is colocated with TS2564 or TS2411. The same anchor is used by ordinary heritage checks and generic-method constraint reports.

Measured exact flips:

• apparentTypeSubtyping: 0/1 -> 1/1
• apparentTypeSupertype: 0/1 -> 1/1
• subtypingWithObjectMembers: 0/1 -> 1/1
• Exact fixtures 401-500: 70/100 -> 73/100
• Canonical aggregate: 4,898/5,907 -> 4,901/5,907 (82.97%), 1,006 remaining

Change size:

• Production checker logic: 16 insertions and 2 call-site replacements
• Complete checker diff including regressions: 60 insertions, 6 deletions

Verification:

• ts_checker: 3,047/3,047
• Baseline-aware ts_conformance gate: 586/586
• Named exact fixtures: 3/3
• Final exact 401-500 survey: 73/100; the other 27 failure names are unchanged

Commit author and committer are Chris chrisbreuer93@gmail.com; there are no coauthor trailers.

Pushed parity chunk 433f27098 (fix(ts-checker): report generic defaults as assignments).

This ports TypeScript's parameter-initializer reporting path: annotated defaults now go directly through plain TS2322 assignment reporting, as upstream checkVariableLikeDeclaration does. It removes Home's specialized TS5075/TS5082 preflight while retaining the same assignability decision and parameter/property diagnostic anchors.

Measured exact flip:

• genericCallWithObjectTypeArgsAndInitializers: 0/1 -> 1/1
• Exact fixtures 401-500: 73/100 -> 74/100
• Canonical aggregate: 4,901/5,907 -> 4,902/5,907 (82.99%), 1,005 remaining

Change size:

• Production checker code: 9 insertions, 19 deletions
• Complete checker diff including the expanded regression: 18 insertions, 29 deletions

Verification:

• ts_checker: 3,047/3,047
• Baseline-aware ts_conformance gate: 586/586
• Named exact fixture: 1/1
• Final exact 401-500 survey: 74/100; the other 26 failure names are unchanged

Commit author and committer are Chris chrisbreuer93@gmail.com; there are no coauthor trailers.

Pushed parity chunk de6e1732b (fix(ts-checker): preserve tuple literal write bounds).

This ports TypeScript's fixed-tuple literal write behavior. Numeric literal write targets now bypass the broad number-index resolver and use the existing tuple slot/range path: in-range writes select the precise slot, rest writes retain the rest element, and out-of-bounds writes emit TS2493 while resolving the target to undefined. Negative tuple indices use the same fixed-range path.

Measured exact flip:

• genericCallWithTupleType: 0/1 -> 1/1
• Exact fixtures 401-500: 74/100 -> 75/100
• Canonical aggregate: 4,902/5,907 -> 4,903/5,907 (83.00%), 1,004 remaining

Change size:

• Production checker logic: 10 insertions and 1 replacement
• Complete checker diff including regression: 22 insertions, 1 deletion

Verification:

• ts_checker: 3,048/3,048
• Baseline-aware ts_conformance gate: 586/586
• Named exact fixture: 1/1
• Final exact 401-500 survey: 75/100; the other 25 failure names are unchanged

Commit author and committer are Chris chrisbreuer93@gmail.com; there are no coauthor trailers.

Pushed parity chunk 6a005d16d (fix(ts-checker): preserve generic instanceof identity).

This ports generic class identity through direct instanceof narrowing. Flow filtering now recovers class identity through substitutions and intersections, preserves the original matching generic union constituent, and uses the same identity for false-branch subtraction and heritage checks.

For a mismatching generic call with no inference candidate, diagnostic display now instantiates the target parameter from its default, constraint, or unknown. This produces TypeScript's B<T> -> A<unknown> diagnostic without tightening overloaded callback checking before Home has full multi-signature candidate merging.

Measured exact flip:

• narrowingGenericTypeFromInstanceof01: 0/1 -> 1/1
• genericCallWithFunctionTypedArguments3 remains 1/1 as a protected higher-order regression
• Exact fixtures 401-500: 75/100 -> 76/100
• Canonical aggregate: 4,903/5,907 -> 4,904/5,907 (83.02%), 1,003 remaining

Change size:

• Production checker logic: 39 insertions, 6 deletions
• Complete checker diff including regression: 55 insertions, 6 deletions

Verification:

• ts_checker: 3,049/3,049
• Baseline-aware ts_conformance gate: 586/586
• Named exact fixtures: 2/2
• Final exact 401-500 survey: 76/100; the other 24 failure names are unchanged

Commit author and committer are Chris chrisbreuer93@gmail.com; there are no coauthor trailers.

TypeScript parity progress: optional signature normalization

Pushed ae4d68ebf (fix(ts-checker): normalize optional signature displays).

This chunk ports TypeScript's optional-signature display normalization:

• union containers are now inspected before aggregate undefined flags, preventing unknown | undefined from collapsing to never
• optional callable parameters normalize unknown | undefined to unknown
• non-strict optional signatures omit their injected undefined
• strict ordinary unions such as string | undefined remain visible
• all callable diagnostic renderers now use the same normalization

Measured parity impact:

• flipped genericCallWithOverloadedConstructorTypedArguments2
• exact fixtures 401-500: 76/100 -> 77/100
• aggregate exact parity: 4904/5907 -> 4905/5907 (83.04%)
• 1002 exact fixtures remain

Implementation/test size:

• 31 production insertions, 10 production replacements/deletions
• 31 regression-test insertions
• 62 insertions, 10 deletions total

Verification:

• checker: 3050/3050
• baseline-aware conformance: 586/586
• focused upstream exact fixture: 1/1
• exact fixtures 401-500: 77/100

Commit author and committer are Chris <chrisbreuer93@gmail.com> with no coauthors.

Pushed c763f11dc (fix(ts-checker): defer contextual callback inference).

This ports TypeScript's two-pass generic-call inference ordering: ordinary argument candidates now precede callbacks whose parameters require contextual typing. Anonymous function declarations are recognized as function expressions, later scalar literals can fix contextual callback return types, and literal-target callback relations are rebuilt from checked syntax. Generic and fully annotated callbacks remain in the ordinary inference pass, preserving string-literal constraint behavior.

Parity impact:

• exact fixtures 401-500: 77/100 -> 79/100
• aggregate exact parity: 4905/5907 -> 4907/5907 (83.07%)
• remaining exact fixtures: 1002 -> 1000
• flipped genericCallWithFunctionTypedArguments
• flipped genericClassWithFunctionTypedMemberArguments
• no new exact failures

Scope:

• checker implementation: +88/-23 lines
• focused regression coverage: +18 lines

Verification:

• checker: 3051/3051
• baseline-aware conformance: 586/586
• exact 401-500 survey: 79/100

Pushed d14e61b00 (fix(ts-checker): instantiate overloaded callback signatures).

This ports contextual generic-signature instantiation for overloaded callback arguments. Every target call signature must now find a compatible source signature after source-owned type parameters are inferred from the target parameter and return types. Genuine mismatches also render full generic callback and anonymous overload-set names instead of the positional TS2345 fallback.

Parity impact:

• exact fixtures 401-500: 79/100 -> 80/100
• aggregate exact parity: 4907/5907 -> 4908/5907 (83.09%)
• remaining exact fixtures: 1000 -> 999
• flipped genericCallWithOverloadedFunctionTypedArguments2
• no new exact failures

Scope:

• checker implementation: +64 lines
• focused regression coverage: +17 lines

Verification:

• overload-focused checker tests: 68/68
• full checker: 3052/3052
• baseline-aware conformance: 586/586
• exact 401-500 survey: 80/100

Pushed d2433e3c1 (fix(ts-checker): block NoInfer inference candidates).

This ports real NoInfer<T> behavior into the Home TypeScript checker: a fresh branded internal wrapper blocks candidate collection through direct, array, object-property, whole-object, and callback-return positions, then erases during substitution, assignability, and display. Primitive-constrained inference now preserves literal candidates, and nested mismatches elaborate with TypeScript-compatible TS2322/TS2741 diagnostics. The fresh brand plus checker-owned payload map prevents ordinary source objects named __home_no_infer from colliding with the intrinsic.

Measured parity movement:

• exact fixtures 401-500: 80/100 -> 81/100
• flipped fixture: noInfer
• aggregate exact parity: 4908/5907 -> 4909/5907 (83.10%)
• remaining exact fixtures: 998
• checker diff: +141/-12 lines with 2 regression tests

Validation:

• focused NoInfer group: 6/6
• full checker: 3054/3054
• baseline-aware gate: 586/586
• exact-window failure-name delta: only noInfer was removed; the other 19 failures were unchanged.

Pushed 18937a534 (fix(ts-checker): instantiate generic heritage signatures).

This replaces the checker's blanket leniency for generic interface-member signatures with TypeScript-style contextual signature instantiation. Generic child call/construct signatures now infer from the base context, discard candidates that violate constraints, complete from defaults/constraints, compare parameters contravariantly and returns covariantly, and use alpha-renamed comparison for generic-to-generic signatures (including array return elements).

Measured parity movement:

• exact fixtures 401-500: 81/100 -> 83/100
• flipped fixtures: callSignatureAssignabilityInInheritance3, constructSignatureAssignabilityInInheritance3
• recovered exact diagnostics: 14 TS2430 headers
• aggregate exact parity: 4909/5907 -> 4911/5907 (83.14%)
• remaining exact fixtures: 996
• checker diff: +75/-3 lines with 1 focused regression test

Validation:

• focused heritage test: 2/2 including the checker root test
• full checker: 3055/3055
• baseline-aware gate: 586/586
• exact-window failure-name delta: only the two intended inheritance fixtures were removed; the other 17 failures were unchanged.

Pushed 857064666 (fix(ts-checker): report weak implements mismatches).

• Ports the relation-specific weak-type implements diagnostic: no shared properties against an all-optional target now emits TS2559, while overlapping incompatible properties retain TS2420.
• Applies consistently to initial, refined, and JSDoc class-implements paths.
• Flips subtypingWithObjectMembers5 and corrects 3 TS2420 diagnostics to TS2559.
• Exact 401-500: 83/100 -> 84/100.
• Aggregate exact parity: 4911/5907 -> 4912/5907 (83.16%, 995 remaining).
• Verification: checker 3056/3056, baseline gate 586/586.
• Scope: implementation +40/-25 lines, regression coverage +14 lines.

Pushed d679343f6 (fix(ts-checker): resolve overloaded callback methods).

This ports generic overloaded-callback method resolution: inference now uses the final source overload, preserves same-family generic instance arguments, instantiates member overloads before applicability checks, validates all source overloads, anchors TS2769 on the first argument, and renders deduplicated concrete overload diagnostics.

Parity impact:

• exact fixtures 401-500: 84 -> 85/100
• flipped: genericCallToOverloadedMethodWithOverloadedArguments (all 4 expected diagnostics)
• aggregate exact parity: 4912 -> 4913/5907 (83.17%)
• remaining: 994

Validation:

• checker: 3057/3057
• baseline gate: 586/586
• scope: checker implementation +148/-5 lines; focused regression coverage +31 lines

Commit: https://github.com/home-lang/home/commit/d679343f60bdf45f3490e62d1ae2430f4971f238

Pushed 108329e84 (fix(ts-checker): keep enum assignments nominal).

This narrows generic-intersection assignment acceptance to sources that actually contain the target type parameter, preventing branded numeric enums from flowing into arbitrary generic slots. Enum identities also bypass structural single-missing-property selection, preserving nominal TS2322 diagnostics for class/interface targets.

Parity impact:

• exact fixtures 401-500: 85 -> 86/100
• flipped: enumAssignability
• corrected diagnostics: 3 restored generic-target TS2322 errors + 2 TS2741 -> TS2322 corrections
• aggregate exact parity: 4913 -> 4914/5907 (83.19%)
• remaining: 993

Validation:

• focused exact filter: 2/2
• checker: 3058/3058
• baseline gate: 586/586
• scope: checker implementation +22/-13 lines; focused regression coverage +28 lines

Commit: https://github.com/home-lang/home/commit/108329e84ddedf000389261c7dc155160373eaf8

Pushed 764539742 (fix(ts-checker): preserve optional source signatures).

Assignment diagnostics now retain function-expression provenance: optional arrow/function parameters omit the checker-synthesized | undefined on the source side, while declared target signatures continue to use strict-null expansion.

Parity impact:

• exact fixtures 401-500: 86 -> 87/100
• flipped: assignmentCompatWithCallSignaturesWithRestParameters
• corrected: all 5 source-signature text mismatches
• aggregate exact parity: 4914 -> 4915/5907 (83.21%)
• remaining: 992

Validation:

• focused exact fixture: 1/1
• checker: 3059/3059
• baseline gate: 586/586
• scope: checker implementation +24/-1 lines; focused regression coverage +17 lines

Commit: https://github.com/home-lang/home/commit/7645397429024842002ea6e2f08052563c038b9e

Pushed 14219ab24 (fix(ts-checker): enforce constrained heritage relations).

• Heritage relations now treat target type parameters as declared slots rather than inference slots.
• Constrained source parameters recursively compare instantiated generic constraints, including mutual, reverse-mutual, self-recursive, and namespace-scoped cases.
• Equivalent substituted parameter IDs are preserved by declared name, while unrelated T/U/V parameters remain incompatible.
• TS2416 now renders child and extends names from syntax, retaining forms such as D2<T, U, V> and Base<T> inside namespaces.
• Restored the complete expected TS2411/TS2416 sets for subtypesOfTypeParameterWithRecursiveConstraints and subtypesOfTypeParameterWithConstraints4; the 33 prior baseline diff removals are now reduced to a separate same-position ordering mismatch.
• Scope: 144 insertions, 18 deletions, one regression covering all five constrained-relation shapes.

Verification: focused checker 2/2, full ts_checker 3060/3060, parity gate 586/586. The exact fixture flip is isolated to the next conformance ordering chunk.

Pushed 31b1fb5d0 (fix(ts-checker): compare generic heritage indexers).

The constrained-heritage relation now compares string, number, and symbol index signatures instead of returning success after an empty member walk. Number-index targets accept either a source number index or the JavaScript-compatible string-index fallback, while index value types remain universally quantified.

Measured impact:

• Restores the three missing generic TS2420 diagnostics in subtypingWithNumericIndexer5.
• Flips that exact fixture from failing back to passing.
• Adds 50 lines, including one regression with one concrete valid implementation and three invalid generic implementations.
• Focused checker 2/2, full ts_checker 3061/3061, parity gate 586/586.
• Combined affected exact set is 6/6; the remaining conformance ordering edit is still isolated and uncommitted.

Pushed dd878cfcd (fix(ts-conformance): order index member diagnostics).

The exact formatter now gives TS2411 priority only over TS2416 and TS2564 at the same property anchor. All other pairs retain the span-length tie-break, preserving TS2393-before-TS2411 for duplicate computed methods and TS2454-before-TS2322 for tuple assignments.

Measured impact:

• Flips subtypesOfTypeParameterWithRecursiveConstraints and subtypesOfTypeParameterWithConstraints4 exact.
• 401-500: 87/100 -> 89/100, with no regression among the other 98 fixtures.
• Affected exact set: 6/6.
• Full exact corpus: 4915/5907 (83.21%), 992 remaining.
• Scope: 6 inserted lines.

The paired old/current manifest audit also found and repaired the generic numeric-index regression in 31b1fb5d0; computed-property and tuple ordering remain exact.

Pushed 7709634ab (fix(ts-checker): preserve inferential callback annotations).

• Keeps explicit callback parameter annotations authoritative through contextual checking, generic inference, assignability, and TS2345 rendering.
• Preserves nested returned-function literal types, compares callable return shapes recursively, retains Object display identity, and emits structural argument-diagnostic chains.
• Exact flips: genericCallWithGenericSignatureArguments3 and typeArgumentInferenceErrors.
• Exact window 401-500: 89/100 -> 90/100.
• Full exact corpus: 4915/5907 -> 4917/5907 (+2, 990 remaining, no losses).
• Verification: focused fixture 1/1, callback family 3/3, checker 3062/3062, conformance gate 586/586, full exact 4917/5907.
• Change size: 174 insertions, 12 deletions, including one focused regression test.

Authored and committed as Chris with no co-author trailers.

Pushed 09a1ee0d18c72511c26cf78a2d541a9fc12a7194 (fix(ts-checker): instantiate generic callbacks contextually).

This ports contextual generic-signature instantiation semantics into the checker: parameter candidates are collected independently, compatible candidates merge to a common supertype, disjoint candidates fall back to unknown, and return inference remains lower priority. Failed callback instantiation now propagates to the enclosing call result, generic callable diagnostics retain <T>, and repeated-variable union display distinguishes canonical primitive ordering from source-preserved object-shape unions.

Measured parity impact:

• contextualSignatureInstantiation: exact 0/1 -> 1/1
• exact window 401-500: 90/100 -> 91/100
• full exact corpus: 4917/5907 -> 4918/5907
• remaining exact failures: 989
• failure-set comparison: only contextualSignatureInstantiation removed; no failures added
• checker: 3062/3062
• conformance: 1368/1368
• change size: 264 insertions, 11 deletions

Pushed 74509af8af90b4d4e3590fa89a3277c715198268 (fix(ts-checker): type callable unions contextually).

This ports contextual typing for concrete callable unions on direct function assignments and annotated initializers. Shared parameter types are installed when each union branch has a compatible signature, while generic call arguments remain on the staged inferential path. The function-expression classifier now rejects failed concrete primitive return relations instead of letting the structural object fallback accept them vacuously.

Measured parity impact:

• functionExpressionContextualTyping2: exact 0/1 -> 1/1
• full exact corpus: 4918/5907 -> 4919/5907
• remaining exact failures: 988
• failure-set comparison: only functionExpressionContextualTyping2 removed; no failures added
• inferential callback guard set: 5/5 exact
• checker: 3063/3063
• conformance: 1368/1368
• change size: 44 insertions, 0 deletions

Pushed 41830ce0f (fix(ts-checker): reject abstract constructor arguments).

This moves abstract-constructor compatibility ahead of structural constructor-signature matching for call arguments, reusing the existing TS2345 + TS2517 diagnostic chain while preserving concrete-to-abstract assignability.

Parity impact:

• classAbstractFactoryFunction: 0/1 -> 1/1 exact
• full exact corpus: 4919/5907 -> 4920/5907 (987 remaining, no added failures)
• checker: 3064/3064
• conformance: 1368/1368
• implementation: 34 insertions, 0 deletions, including focused bidirectional regression coverage

Pushed cd0a1abda (fix(ts-checker): require trailing overload implementation).

Bodyless class-method implementation requirements now follow the final overload declaration: trailing abstract signatures stay implementation-free, while trailing non-abstract signatures emit TS2391 even when the group begins abstract.

Parity impact:

• classAbstractInstantiations2: 0/1 -> 1/1 exact
• full exact corpus: 4920/5907 -> 4921/5907 (986 remaining, no added failures)
• focused TS2512 guard: 3/3
• checker: 3064/3064
• conformance: 1368/1368
• implementation: 3 insertions, 1 deletion

Pushed 94288a2bf (fix(ts-checker): compare accessor overrides directly).

Inherited members with different method kinds now use direct type assignability, preventing zero-argument signature return unwrapping from accepting () => number as an accessor number. Compatible method/function-property overrides and method bivariance remain unchanged.

Parity impact:

• derivedClassFunctionOverridesBaseClassAccessor: 0/1 -> 1/1 exact
• full exact corpus: 4921/5907 -> 4922/5907 (985 remaining, no added failures)
• focused override family: 4/4
• checker: 3064/3064
• conformance: 1368/1368
• implementation: 8 insertions, 0 deletions

Pushed 10ef66820 (fix(ts-checker): respect local heritage shadows).

Class heritage now resolves local variable declarations before global class tables, infers unannotated initializer types, widens mutable literal bindings, and restricts callable rendering so primitive TS2507 messages retain names such as number. Forward class references remain on their existing resolver path.

Parity impact:

• classExtendsShadowedConstructorFunction: 0/1 -> 1/1 exact
• full exact corpus: 4922/5907 -> 4923/5907 (984 remaining, no added failures)
• focused shadow and forward-class guards: 2/2
• checker: 3065/3065
• conformance: 1368/1368
• implementation: 49 insertions, 5 deletions, including one focused regression test

Pushed 215cb8a77 (fix(ts-checker): report non-constructor heritage expressions).

Literal and other non-identifier class heritage expressions now share TS2507 reporting with preserved source literal types. Local variable heritage also emits TS2454 for uninitialized non-nullish bindings, while extends null remains accepted as TypeScript requires.

Parity impact:

• classExtendingNonConstructor: 0/1 -> 1/1 exact
• full exact corpus: 4923/5907 -> 4924/5907 (983 remaining, no added failures)
• focused non-constructor heritage guard: 2/2
• checker: 3066/3066
• conformance: 1368/1368
• implementation: 52 insertions, 3 deletions, including one focused regression test

Pushed a3a463d6c (fix(ts-checker): distinguish runtime namespace assignments).

Namespace assignment targets now distinguish empty/type-only namespaces from runtime namespaces. Empty namespaces retain TS2708 without a duplicate TS2631; runtime namespaces continue to reject reassignment with TS2631. The commit body links back to #69.

Parity impact:

• assignments: 0/1 -> 1/1 exact
• full exact corpus: 4924/5907 -> 4925/5907 (982 remaining, no added failures)
• focused namespace assignment guard: 2/2
• checker: 3067/3067
• conformance: 1368/1368
• implementation: 26 insertions, 4 deletions, including one focused regression test

Pushed 02235ff63 (fix(ts-checker): resolve ordinary module augmentations).

String-literal module augmentations in ordinary external-module files now participate in TS2664 target resolution, including empty bodies. Resolved targets and declaration files remain exempt, and the commit body links back to #69.

Parity impact:

• ambientExternalModuleInsideNonAmbientExternalModule: 0/1 -> 1/1 exact
• full exact corpus: 4925/5907 -> 4926/5907 (981 remaining, no added failures)
• focused missing-augmentation guard: 2/2
• checker: 3068/3068
• conformance: 1368/1368
• implementation: 20 insertions, 3 deletions, including one focused regression test

Pushed 7fa91c13c (fix(ts-checker): merge ambient module export surfaces).

Home now aggregates export facts across every visible exact or wildcard ambient module declaration, including implicit interface/type exports and known missing names. Named-import diagnostics preserve wildcard module symbol names, emit bare TS2305 for trusted misses, and avoid unrelated local spelling suggestions. The commit body links back to #69.

Parity impact:

• ambientDeclarationsPatterns_merging1: 0/1 -> 1/1 exact
• ambientDeclarationsPatterns_merging2: 0/1 -> 1/1 exact
• focused ambient merging set: 1/3 -> 3/3 exact
• typeReferenceRelatedFiles guard: 1/1 exact
• full exact corpus: 4926/5907 -> 4928/5907 (979 remaining, no added failures)
• ts_program: 58/58
• checker: 3069/3069
• conformance: 1368/1368
• implementation: 197 insertions, 54 deletions, including two focused regression tests

Pushed 22768c8cf (fix(ts-checker): instantiate omitted generic class arguments).

Implicit-constructor generic classes now instantiate omitted type parameters through declared defaults, constraints, then unknown. Explicit-constructor classes remain on the established constructor-inference path, and explicit mapped-type class instantiations avoid redundant substitution. The commit body links back to #69.

Parity impact:

• callGenericFunctionWithZeroTypeArguments: 0/1 -> 1/1 exact
• full exact corpus: 4928/5907 -> 4929/5907 (978 remaining, no added failures)
• mappedTypeErrors stress guard: completes without a substitution crash
• checker: 3070/3070
• conformance: 1368/1368
• implementation: 77 insertions, 20 deletions, including one focused positive/negative regression test

Pushed df3d186d2 (fix(ts-checker): reject unrelated generic variable initializers).

This ports variable-declaration assignability for unrelated bare type parameters: a comma initializer whose value is T2 now correctly reports TS2322 when the declared slot is unrelated T1. The declaration path preserves valid same-parameter and transitive-constraint assignments, delegates inferred indexed-access values to structural relation, and excludes flow-narrowed union/intersection composites from the bare-parameter check.

Parity movement:

• commaOperatorOtherInvalidOperation: 0/1 -> 1/1 exact
• Full exact corpus: 4929/5907 -> 4930/5907 (+1)
• Remaining exact failures: 977
• Newly failing fixtures: 0
• Patch size: +48/-0 lines in packages/ts_checker/src/check.zig

Verification:

• focused checker regression: 2/2
• checker suite: 3071/3071
• conformance suite: 1368/1368
• exact corpus: 4930/5907, with a failure-set diff containing only the intended removal

Tracks #69.

Pushed 7e60d619a (fix(ts-parser): recover missing logical-not operands).

Parity impact:

• logicalNotOperatorInvalidOperations: 0/1 -> 1/1 exact
• Full exact corpus: 4930/5907 -> 4931/5907
• Remaining failures: 977 -> 976
• New failures: 0
• Change size: 38 insertions across 2 files

Implementation:

• Recover a lone logical-not operator at an operand stop token after emitting TS1109.
• Synthesize a checker-safe numeric operand so parsing retains the complete source file without secondary diagnostics.
• Add parser and checker regressions for the upstream malformed-initializer sequence.

Verification:

• parser: 736/736
• checker: 3072/3072
• conformance: 1368/1368
• exact TypeScript corpus: 4931/5907, no regressions

Tracks #69.

Pushed 1d52640e8 (fix(ts-parser): recover invalid bitwise-not declarations).

Parity impact:

• bitwiseNotOperatorInvalidOperations: 0/1 -> 1/1 exact
• Full exact corpus: 4931/5907 -> 4932/5907
• Remaining failures: 976 -> 975
• New failures: 0
• Change size: 30 changed lines in 1 file (29 insertions, 1 deletion)

Implementation:

• Recover stray and operand-less ~ forms while preserving the surrounding source file.
• Emit the upstream TS1005/TS1109 sequence for a stray initializer tail.
• Emit TS1134 for literal tokens in a variable declaration list and continue parsing.
• Add a parser regression covering all four expected diagnostics.

Verification:

• parser: 737/737
• checker: 3072/3072
• conformance: 1368/1368
• exact TypeScript corpus: 4932/5907, no regressions

Tracks #69.

Pushed 02914ab59 (fix(ts-parser): recover nested var initializers).

Parity impact:

• negateOperatorInvalidOperations: 0/1 -> 1/1 exact (all 11 expected diagnostics)
• Full exact corpus: 4932/5907 -> 4933/5907
• Remaining failures: 975 -> 974
• New failures: 0
• Change size: 101 changed lines across 2 files (100 insertions, 1 deletion)

Implementation:

• Preserve a nested var binding encountered in a malformed initializer expression.
• Attach recovered any metadata to the outer and nested declarations so the later binding naturally emits the upstream TS2403 mismatch.
• Continue through the malformed unary tail and subsequent nullish arithmetic expressions.
• Add parser-shape and checker-message regressions for the complete recovery sequence.

Verification:

• parser: 738/738
• checker: 3073/3073
• conformance: 1368/1368
• exact TypeScript corpus: 4933/5907, no regressions
• rebased focused exact fixture: 1/1

Tracks #69.

Pushed 6c251ce93 (fix(ts-checker): preserve strict-off nullish addition types).

Parity impact:

• bitwiseNotOperatorWithAnyOtherType: 0/1 -> 1/1 exact
• plusOperatorWithAnyOtherType: 0/1 -> 1/1 exact
• Full exact corpus: 4933/5907 -> 4935/5907
• Remaining failures: 974 -> 972
• New failures: 0
• Change size: 49 changed lines in 1 file (42 insertions, 7 deletions)

Implementation:

• Preserve null / undefined operand types for strict-off binary additions under selected unary parents.
• Emit whole-expression TS2365 under +, ~, and delete.
• Retain operand-level TS18050 under !, typeof, and void, avoiding the broader rule that regressed those fixtures during development.
• Add exact-message coverage for all three nullish operand pairs.

Verification:

• checker: 3074/3074
• conformance: 1368/1368
• focused parent-context matrix: 5/6 exact; only the independently failing delete fixture remains
• exact TypeScript corpus: 4935/5907, no regressions
• rebased focused unit test: 2/2

Tracks #69.