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.

Pushed baseline-policy correction bb7408532 (fix(ts-parity): fall back to original ts baselines).

This implements TS_PORT_DIVERGENCE_NOTES.md: tsgo-generated baselines remain primary, while original TypeScript baselines are used only when tsgo has no matching output for an unported feature.

• Recovered the 3 resolver fixtures exactly without suppressing diagnostics (3/3 targeted).
• Scope: 1 conformance file, +32/-1, plus 1 fallback-path regression test.
• Authoritative leading inventory under the corrected contract: 982/1,000, 18 failures.
• The prior 997/1,000 projection used only the incomplete tsgo baseline set and is superseded.

The 18 newly visible failures cluster into union/alias identity rendering, generic constraint diagnostic selection, template-literal relation identity, unique-symbol JS validation, and mapped-key identity.

Pushed two direct-main parity chunks as Chris (no coauthors):

• ad1e57df0 fix(ts-parity): close leading exact conformance slice — 154 additions / 18 deletions in the checker. Flips all 18 corrected layered-baseline failures covering repeated alias identity, conditional distributivity preservation, callable/construct union diagnostics, heritage constraint leaves, and checked-JS unique-symbol modifiers.
• 95ab2e2d6 test(ts-parity): layer fallback into category survey — 3 additions. Applies the documented original-TypeScript fallback to the baseline-aware category survey.

Measured results against canonical tsgo 24fabe95acba758c05fcb349bf427a3a0c8ad676 plus original-TS fallback only when tsgo has no baseline:

• authoritative START=0 LIMIT=1000: 982/1000 -> 1000/1000 exact, no skips
• baseline-aware category survey: 585/586 -> 586/586, including unique-symbol 7/7
• focused corrected variants: 21/21 exact (substring expansion included 3 related variants)
• ts_driver: clean
• broad ts_checker: 3716/3765, with the remaining 49 known red assertions retained as the next package-level backlog

The leading 1,000-case window is now fully exact under the corrected layered baseline inventory. Continuing with START=1000 LIMIT=1000.

Parity checkpoint: exact cases 1,000-1,999 are now 1,000/1,000, so the leading exact range is 2,000/2,000. The baseline-aware category survey remains 586/586.

Pushed as three small conventional commits:

• 062c361d2 fix(ts-checker): close class diagnostic parity gaps - 8 focused regressions covering private/protected receiver identity, duplicate private declarations, merged class instances, static-super/Reflect collisions, global receivers, and mixin displays.
• f09848d6b fix(ts-driver): port stage-3 decorator helpers - 4 helper contracts (__esDecorate, __runInitializers, __propKey, __setFunctionName) across direct and program compilation.
• ab60e1eda fix(ts-conformance): route exact emit targets - 11 target generations through all 3 corpus execution routes.

Verification:

• exact 1,000-case slice: 1,000/1,000
• baseline-aware categories: 586/586
• ts_driver: pass
• ts_program: pass
• checker: 3,724/3,773, retaining the same 49 known failures while all 8 new regressions pass
• conformance unit suite retains the same 6 known failures; no new unit failures

Continuing with exact cases 2,000-2,999.

Exact parity checkpoint: cases 2,000-2,999 are now 1,000/1,000, bringing the leading exact range to 3,000/3,000.

Pushed as two small conventional commits:

• 5dd8529c5 fix(ts-checker): close checked JS assignment gaps - preserves undefined CommonJS flow, checks method writes against constructor-inferred members, diagnoses cross-file class expandos, and renders chained export-assignment namespaces. Adds 2 regressions and strengthens 2 existing contracts.
• f39943154 fix(ts-program): collect chained CommonJS exports - records whole exports through exports = module.exports = C while retaining named export metadata. Adds 1 program regression.

Verification:

• exact cases 2,000-2,999: 1,000/1,000 (up from 994/1,000)
• targeted original failures: 6/6
• interaction regression contextualTypedSpecialAssignment: pass
• ts_program: pass
• checker: 3,726/3,775, retaining the same 49 known failures while both new regressions pass

Continuing with exact cases 3,000-3,999.

Exact parity checkpoint: 3,879 / 4,000 leading fixtures

Pushed 884513083 (fix(ts-checker): follow tsgo checked JS namespace semantics) as Chris with no coauthors.

• Fresh exact window 3000-3999: 879 / 1,000 (up from 870, +9 flips)
• Leading exact total: 3,879 / 4,000
• Focused current-tsgo checked-JS families: 7 / 7 cumulatively across expanded variants
• Program suite: passing
• Change size: 203 insertions / 104 deletions across checker + program
• Coverage: five checker contracts and one program contract

The batch removed two obsolete fallback-era diagnostics, resolved qualified JSDoc typedefs before namespace errors, separated type-only/value expando metadata, and used future CommonJS assignment types for declaration checking. The remaining 121 fixtures are now being grouped by shared compiler behavior.

Parity checkpoint at 34c846851 (fix(ts-checker): align checked JS declaration flow):

• Leading exact tsgo corpus is now 3,888/4,000 (up +9 from the prior 3,879 checkpoint).
• This chunk flipped 3/3 exact fixtures: jsDeclarationsClassLikeHeuristic, jsDeclarationsModuleReferenceHasEmit, and jsDeclarationsTypeReassignmentFromDeclaration2.
• Broad checker: 3,737/3,784, with the same 47 known failures and all 3 new checker contracts passing.
• Parser: 842/843; the sole failure remains the unrelated recovered-JavaScript-modifier TS8009 count.
• Changes were pushed directly to main as Chris with no coauthor.

TypeScript parity checkpoint

Pushed four small conventional commits directly to main as Chris:

• ca1b6733a fix(ts-checker): recognize declaration-only JSDoc typedefs — flipped 3 checker contracts.
• 9da6316fc build: add focused TypeScript checker tests — added -Dts-checker-test-filter, reducing focused feedback from roughly 6 minutes to about 20 seconds.
• 489275840 fix(ts-checker): preserve JavaScript base constructors — flipped the cached checked-JS heritage contract.
• 1164ad271 fix(ts-checker): preserve JavaScript constructor instances — flipped 6 more contracts across direct-this constructor inference, prototype object this, accurate missing-member diagnostics, and inherited constructor @template scope for direct/object/qualified prototype methods.

Latest authoritative checker sweep: 3,747/3,784 passing (99.02%), up from 3,737/3,784 across this checkpoint, with 37 known failures and no regressions in the latest batch. The full checkjs prototype focused group is green.

Other established floors remain:

• exact current-tsgo leading corpus: 3,888/4,000
• baseline-aware category survey: 586/586
• parser: 842/843, with the sole known JavaScript modifier recovery diagnostic mismatch

Next work stays on the remaining checker clusters before another expensive exact-corpus sweep.

Pushed ffc1f46d1 (fix(ts-checker): align current JSDoc diagnostics) directly to main as Chris.

This batch:

• preserves exact braced JSDoc text for current tsgo parsing;
• reports bare @satisfies and empty generic syntax without stale cascades;
• keeps Closure-style function(...) JSDoc types malformed per current tsgo;
• renders contextual async callback Promise signatures correctly;
• deduplicates raw-checker TS2741 diagnostics;
• updates focused regressions to the canonical tsgo contracts.

Measured progress:

• full checker: 3,747/3,784 -> 3,754/3,784 (+7, no new failure names);
• affected exact tsgo fixtures: 7/7;
• established exact leading corpus remains 3,888/4,000;
• baseline-aware category survey remains 586/586;
• parser remains 842/843, with the one known unrelated recovered-JavaScript-modifier diagnostic gap.

The checker now has 30 focused failures remaining.

Pushed ef0ec09cc (fix(ts-checker): align relation identity with tsgo) directly to main as Chris Breuer, with no coauthor trailers.

This chunk changes 118 lines in packages/ts_checker/src/check.zig (74 insertions, 44 deletions): function expandos now bind to their resolved declaration across block shadowing, uppercase Object relations distinguish weak all-optional targets from required targets, indexed sources satisfy open any string indexes, and five local assertions now use current tsgo diagnostic surfaces.

Verification:

• full checker: 3,754/3,784 -> 3,761/3,784 (+7, 23 remaining)
• focused checker groups: 6/6 passing, covering 7 tests
• targeted canonical exact batch: 8/9 exact; only the pre-existing jsDeclarationsReactComponents mismatch remains
• exact fixtures now matching include narrowingGenericTypeFromInstanceof01, typeGuardIntersectionTypes, mappedTypeErrors, mappedTypeErrors2, objectTypeWithStringAndNumberIndexSignatureToAny, constructorParameterProperties2, typeFromPropertyAssignment29, and typeFromPropertyAssignment36
• git diff --check: clean

Pushed de8004b6e (fix(ts-checker): adopt current tsgo JavaScript divergence) directly to main as Chris Breuer, without coauthors. This flips 8 previously failing checker cases to the current tsgo contracts (rather than inherited TypeScript baselines): void-zero JS expandos, cross-file qualified JSDoc namespaces, chained CommonJS constructor values, string-literal CommonJS exports, bare/variable constructor this, and cross-file class/JS conflicts. It also removes duplicate TS2339 emission for the same member-access node. Focused current tsgo checker group is 9/9 passing. Based on the previous 3761/3784 full run this should move the checker floor to at least 3769/3784; I am batching the remaining implementation fixes before the next full run.

Pushed 83103570f (test(ts-checker): track current tsgo diagnostic shifts) directly to main as Chris Breuer, without coauthors. This flips 6 more stale checker contracts to the canonical tsgo baselines: ambient namespace prototype TS2339, object-call TS2741, four auto-accessor duplicate diagnostics, malformed @template without the legacy unresolved-name error, enum initializer TS2739, and current checked-JS this diagnostics. The focused current-tsgo group grew from 9/9 to 15/15. Together with the prior shared TS2339 deduplication, the old 23-failure list now has 15 corrected cases plus 1 additional implementation case passing; 7 genuine checker gaps remain before the next full run.

Checker parity batch pushed as 0deb23a (Chris only, no coauthors).\n\n- Closed the final 8 known checker contracts across checked-JS member flow, cross-file prototype ownership, CommonJS whole/rebound exports, private-origin repeated vars, qualified namespace class parameters, and ECMAScript private-brand elaboration.\n- Updated 5 stale assertions to the current tsgo diagnostic shape, including the canonical jsTypedefMergedWithModuleExportProperty baseline (1x TS2339 + TS2309).\n- Full checker result: 3,784/3,784 passing, up 23 from the last full 3,761/3,784 audit.\n\nNext parity work moves to the remaining exact corpus windows and the single parser TS8009 gap.

Pushed 525792858 (fix(ts-checker): align destructuring argument relations) directly to main as Chris.

• Flipped 4 current-tsgo exact contracts: iterableArrayPattern17, iterableArrayPattern18, destructuringParameterDeclaration1ES6, and destructuringParameterDeclaration4.
• Exact 4000-4019 is now 20/20, up from 16/20.
• Added rest-argument missing-property elaboration, nullish default-array element reporting after outer relation failure, nested tuple element priority over width, and current Array remainder text (24).
• Focused verification: 4/4.

Next exact survey inventory: 4020-4099 is 65/80; failures are clustered around self-reference flow, destructuring control flow, ES5 iterable element precision, parser anchors, and object-rest diagnostics.

Pushed 3ea4342b5 (fix(ts-checker): preserve destructuring source context) directly to main as Chris.

• Flipped 6 current-tsgo exact fixtures.
• Exact 4020-4099 improved from 65/80 to 71/80.
• 4020-4039 is now 20/20; 4060-4079 is 19/20.
• Preserved positional array-literal and rest-source context, gated circular TS7022 on noImplicitAny, respected var hoisting for TS2448, retained iterator source names, and anchored mixed Map overload diagnostics at the incompatible value.
• Focused verification: 6/6.
• Adjacent for-of39 exceeded a 180-second exact audit and is not counted as passing.

Pushed 27440ca fix(ts): align radix and symbol conformance to main as Chris (no coauthor). This batch flipped 9 exact current-tsgo fixtures: 4 binary/octal numeric-property fixtures, 3 well-known-symbol fixtures, iterableArrayPattern7, and typeArgumentInferenceWithClassExpression2. Verification: focused exact 9/9; affected directories 241/255 (14 remaining gaps identified); checker 3,784/3,784; parser 842/843 with the pre-existing TS8009 JavaScript-modifier recovery assertion unchanged. The implementation now canonicalizes arbitrary-length radix keys with JS scientific spelling, preserves anonymous class static/prototype identity, checks symbol-index signature returns, reports current-tsgo duplicate symbol declarations, and scopes Array<t> missing-member diagnostics to the correct destructuring relation.

Pushed a04df0417 (fix(ts-checker): align destructuring width diagnostics) directly to main as Chris Breuer with no coauthors. This flips 3 exact current-tsgo fixtures, moving the 255-fixture affected sweep from 241/255 to 244/255, and also matches 5 additional tuple-bound diagnostics in declarationsAndAssignments. Verification: focused exact 3/3, affected exact 244/255, full ts_checker 3784/3784.

Pushed 171fa99d4 (fix(ts-checker): align nested binding diagnostics) directly to main as Chris Breuer with no coauthors. This flips 2 exact current-tsgo fixtures, moving the 255-fixture affected sweep from 244/255 to 246/255. It closes 4 residual declarationsAndAssignments mismatches and all 4 diagnostics in destructuringParameterDeclaration8. Verification: focused exact 3/3 (including the optional-default regression fixture), affected exact 246/255, full ts_checker 3784/3784.

Pushed e5c75791d (fix(ts-checker): align nested default diagnostics) to main as Chris only.

Parity movement:

• Added diagnostic-only recursive comparison of array arguments against array binding-pattern defaults.
• Preserved inferred signature types while reporting exact null/undefined leaf targets, including literal true/false display.
• Flipped 2 exact tsgo fixtures: destructuringParameterDeclaration1ES5 and destructuringParameterDeclaration1ES5iterable.
• Affected exact slice: 246/255 -> 248/255 (7 remaining).
• Full checker regression suite: 3,784/3,784 passing.

Next batch is the remaining destructuring control-flow/grammar recovery and computed-symbol accessor parity.

Pushed c67a022dd (fix(ts-checker): align destructuring recovery diagnostics) to main as Chris only.

Parity movement:

• Removed stale contextual TS2322 returns from unannotated duplicate getters after TS2300 recovery.
• Added apparent primitive wrapper diagnostics for object assignment patterns, including static property and dynamic index keys.
• Preserved declared optional tuple element flow instead of overriding it with a shorter initializer tuple.
• Restored parenthesized object-rest anchors, TS2701 target checks, and nested array iterator validation.
• Flipped 3 exact tsgo fixtures: symbolDeclarationEmit12, destructuringControlFlow, and restPropertyWithBindingPattern.
• Affected exact slice: 248/255 -> 251/255 (4 remaining).
• Full checker regression suite: 3,784/3,784 passing.

Remaining in this focused cluster: destructuringParameterProperties3 generic tuple inference plus three malformed destructuring parser-recovery fixtures.

Pushed ab204f7a8 fix(ts-checker): infer positional tuple candidates directly to main (Chris only, no coauthors). This adds positional candidate collection for direct mutable tuple type parameters, preserves whole-structure inference for const type parameters, and merges repeated nullish candidates. Exact affected parity moved 251/255 -> 252/255 by flipping destructuringParameterProperties3; the full checker remains 3,784/3,784. The affected slice now has only three malformed parser-recovery fixtures left.

Pushed 04a341f92 fix(ts-checker): recover malformed binding patterns directly to main (Chris only, no coauthors). The parser now preserves HIR after malformed object bindings and missing array closers; the checker ignores zero-width names for property shapes, handles primitive/empty-object unions, respects explicit : any, and checks nested binding defaults. Exact affected parity moved 252/255 -> 253/255 by flipping destructuringObjectBindingPatternAndAssignment3. Verification: checker 3,785/3,785; parser 843/844, with only the pre-existing TS8009 recovery-count test remaining. Two exact affected fixtures remain: destructuringParameterDeclaration2 and destructuringParameterDeclaration6.

Pushed 4abef69a6 (fix(ts-checker): recover destructured parameter contracts) directly to main as Chris.

Parity impact:

• Flipped destructuringParameterDeclaration2 to exact tsgo parity.
• Affected exact corpus: 253/255 -> 254/255.
• Full checker gate: 3,785/3,785.
• Parser gate: 843/844, with only the existing recovered JavaScript-modifier TS8009 count mismatch (expected 5, found 3).
• Remaining affected failure: destructuringParameterDeclaration6 reserved-word parser recovery.

The port covers declaration-specific object defaults, duplicate binding names across parameter patterns, fixed tuple width diagnostics, recovered object-argument elaboration, and binding-pattern method compatibility without relying on structurally interned signature metadata.

Pushed 9cfc6341b (fix(ts-parser): recover reserved binding parameters) directly to main as Chris, with no coauthors.

Parity impact:

• Flipped destructuringParameterDeclaration6 to exact current-tsgo parity.
• Completed the affected destructuring corpus: 254/255 -> 255/255 exact.
• Target fixture: 1/1 exact, matching all 21 diagnostics in code, message, position, and order.
• Full checker gate: 3,785/3,785.
• Driver suite: passing.
• Parser gate: 845/846, with only the existing recovered JavaScript-modifier TS8009 count mismatch (expected 5, found 3).

The port keeps malformed reserved array bindings recoverable as bodyless declarations, retains checker-visible missing rest bindings, follows tsgo binder suppression only after true syntactic parse errors, and preserves tsgo same-position diagnostic precedence. The checkpoint changes +212/-17 across 3 files.

Pushed c929e8c79 (fix(ts-checker): resolve tagged template context) to main.

This checkpoint ports tagged-template contextual typing and recursive callable-interface behavior into Home:

• selects a unique visible arity-compatible overload for tagged substitutions
• preserves nested generic callback-owned type parameters
• removes eager TS2347 diagnostics only when contextual parameters make the callback callable
• refreshes recursive interface member/index shapes at call/member/index consumers
• prefers direct TS2345 diagnostics for unique arity matches instead of TS2769

Measured parity delta: exact START=4000 LIMIT=1000 advanced 954/1000 -> 960/1000, flipping 6 fixtures with zero regressions:

• taggedTemplateContextualTyping1/2
• taggedTemplateStringsWithTypedTags + ES6
• taggedTemplateStringsWithIncompatibleTypedTags + ES6

Verification: ts_checker 3788/3788, 3 focused tagged-template regressions, zig ast-check, git diff --check, and the full 1,000-case exact slice. The remaining failures in this band are 40.

Pushed 54f45c863 (fix(ts-checker): align literal spread call arity) to main.

This checkpoint:

• counts source array-literal spread elements for fixed call arity
• contextually checks each spread element against its positional parameter
• keeps variable-backed non-tuple spreads on TS2556
• renders optional fixed-parameter arity as the accepted range (0-1)
• stops malformed tagged super<T> recovery before semantic constructor arity checking

Measured parity delta: exact START=4000 LIMIT=1000 advanced 960/1000 -> 962/1000, flipping 2 fixtures with zero regressions: arraySpreadInCall and taggedTemplatesWithTypeArguments2.

Verification: focused exact 2/2, ts_checker 3790/3790, zig ast-check, git diff --check, and the full 1,000-case exact slice. Remaining failures in this band: 38.

Pushed 883a94650 (fix(ts-conformance): parse CR-only directives) to main.

The corpus directive reader now tokenizes both CR and LF line endings. This preserves @target: es6 in CR-only upstream sources instead of silently falling back to ES5 and emitting a spurious TS5107.

Measured parity delta: exact START=4000 LIMIT=1000 advanced 962/1000 -> 963/1000, flipping templateStringMultiline3_ES6 with zero regressions.

Verification: focused CR-only target-selection unit test, focused exact 1/1, forced fresh-cache broad exact slice 963/1000, zig ast-check, and git diff --check. Remaining failures in this band: 37.

Pushed bde76e162 (fix(ts-checker): prioritize invalid computed keys) to main.

Computed-key validation now removes nested TS2872/TS2873 diagnostics only after the key type is proven invalid, immediately before TS2464. This preserves truthiness diagnostics for valid computed keys and keeps object-literal this semantics unchanged.

Measured parity delta: exact START=4000 LIMIT=1000 advanced 963/1000 -> 965/1000, flipping computedPropertyNamesDeclarationEmit6_ES5 and _ES6 with zero regressions.

Verification: focused checker regression, focused exact 2/2, corrected fresh-cache broad exact 965/1000, full ts_checker 3791/3791, zig ast-check, and git diff --check. Remaining failures in this band: 35.

Pushed 8897e53b7 (fix(ts-checker): defer duplicate default classes) to main.

Declaration-space entries now track default-export ownership. When two same-named classes are both default exports, TS2300 is suppressed and the dedicated default-export pass emits the canonical TS2528 pair; ordinary duplicate classes and mixed default/named collisions keep TS2300.

Measured parity delta: exact START=4000 LIMIT=1000 advanced 965/1000 -> 966/1000, flipping multipleDefaultExports03 with zero regressions.

Verification: focused checker regression, focused exact 1/1, fresh-cache broad exact 966/1000, full ts_checker 3792/3792, zig ast-check, and git diff --check. Remaining failures in this band: 34.

Pushed 1848a9b52 (fix(ts-lib): restore Array.concat overloads) to main.

The seeded Array<T> surface now models lib.d.ts's array-only and mixed scalar/array concat overloads separately. Invalid arrays therefore fail the overload set with TS2769, while valid scalar, array, and mixed concat calls remain accepted.

Measured parity delta: exact START=4000 LIMIT=1000 advanced 966/1000 -> 967/1000, flipping iteratorSpreadInArray6 with zero regressions.

Verification: focused checker regression, focused exact 1/1, fresh-cache broad exact 967/1000, full ts_checker 3793/3793, both files zig ast-check, and git diff --check. Remaining failures in this band: 33.

Pushed c0c544772 (fix(ts-driver): validate array spread helper arity).

• Ported the TypeScript ES5 __spreadArray imported-helper contract into both single-file driver and multi-file Program compilation.
• Added first-spread source anchoring, 3-parameter TS2807 validation, missing-helper TS2343 handling, and missing-tslib TS2354 participation.
• Added 161 lines across 2 files, including 2 focused regressions with exact spread spans.
• Flipped arraySpreadImportHelpers; exact 4000-4999 parity advanced 967/1000 -> 968/1000 with zero regressions.
• Verified ts_driver, ts_program, focused exact conformance 1/1, and broad exact conformance 968/1000.

Pushed 69313e3d7 (fix(ts-checker): align conditional expression typing) to main.

Ported tsgo conditional-expression behavior in one focused checker chunk:

• reports void and always-defined callable conditions at the correct conditional sites
• permits numeric 0/1 truthiness idioms while retaining diagnostics for other static numbers
• contextually types conditional callback branches and preserves inferred return types
• preserves explicit callback parameter annotations/arity under strictFunctionTypes
• renders source-owned conditional callback unions without leaking display metadata globally

Parity movement:

• exact conditionalOperator family: 7/7
• exact 4,000-4,999 partition: 968 -> 972/1,000 (4 fixtures flipped, 28 remain)
• checker suite: 3,795/3,795
• implementation scope: 173 additions, 15 deletions in packages/ts_checker/src/check.zig

Pushed 407294e37 (fix(ts-checker): align operator diagnostics) to main.

Ported another focused tsgo operator batch:

• TS2365 now renders callable, widened-enum, namespace, and empty-array operands as () => void, E, typeof M, and never[]
• TS2447 now anchors boolean bitwise diagnostics at the & / | / ^ operator token
• nullish classification now reads real union constituents before overlapping intersection flags, eliminating false TS18049 diagnostics on numeric enum unions

Parity movement:

• exact additionOperatorWith family: 11/11
• exact 4,000-4,999 partition: 972 -> 976/1,000 (4 fixtures flipped, 24 remain)
• checker suite: 3,797/3,797
• implementation scope: 115 additions, 34 deletions in packages/ts_checker/src/check.zig

Pushed fba89758c (fix(ts-checker): align this expression contexts) to main.

Ported two current-tsgo this semantics:

• object-literal methods returning a missing this.member now report the real TS2339 only, without misclassifying the return as recursive TS7023
• class D extends this now renders typeof globalThis in scripts and undefined in external modules

Parity movement:

• exact thisIn family: 4/4
• exact 4,000-4,999 partition: 976 -> 978/1,000 (2 fixtures flipped, 22 remain)
• checker suite: 3,798/3,798
• implementation scope: 30 additions, 36 deletions in packages/ts_checker/src/check.zig

Property-access parity batch landed on main as 8e2decc11 (fix(ts): align property access semantics).

• Preserved the member-access dot after legacy-octal literals (000.toString()), while retaining the existing 01.0 recovery.
• Distributed string | number index keys across string/number index signatures and required whole-union compatibility for numeric-only indexing.
• Matched fresh {} read behavior versus widened assignment-target diagnostics for (options || {}), including exact TS2339/TS7053 anchors and chains.
• Added bracketed Array prototype lookup and source-quoted TS2353 property names.

Exact results:

• Focused property-access family: 14/14.
• START=4000 LIMIT=1000: 978/1000 -> 981/1000 (+3), leaving 19 failures.
• Leading 0..4999: 4,869/5,000 exact.
• Full ts_checker: 3,801/3,801.
• ts_lexer: green.
• ts_parser: 846/847; only the known TS8009 recovery test remains.

The three partition flips are propertyAccessNumericLiterals, propertyAccess, and propertyAccessWidening.

Exact parity progress: malformed object shorthand recovery

Pushed c1c231152 (fix(ts-parser): recover malformed object shorthand).

This ports tsgo's recovery semantics for malformed object-literal members:

• recognizes get/set accessors when a legal property name follows even if the parameter-list ( is missing;
• reports the canonical TS1005 anchor and resumes at the next object member;
• recovers a.b-style shorthand tails as a missing comma without truncating the containing object or namespace;
• keeps TS18004 unresolved-shorthand checking for a while suppressing TS1117 for those syntactically recovered access tails.

Exact fixtures flipped: 2

• objectLiteralShorthandPropertiesErrorWithModule
• objectLiteralShorthandPropertiesErrorFromNotUsingIdentifier

Measured parity

• focused exact: 2/2
• exact partition 4000-4999: 983/1,000, up from 981/1,000
• remaining failures in that partition: 17, down from 19
• leading exact 0-4999: 4,871/5,000, up from 4,869/5,000
• checker: 3,802/3,802
• parser: 848/849; the sole known failure remains the existing TS8009 recovered-JavaScript-modifier diagnostic gap
• canonical tsgo remains pinned at 24fabe95acba758c05fcb349bf427a3a0c8ad676

The remaining 4000-4999 failures are now the tagged-template family, multipleDefaultExports01, incrementAndDecrement, three contextual-typing fixtures, typeAssertions, constAssertions, commaOperatorWithSecondOperandObjectType, typeOfThisGeneral, and the two constructor-signature comparison fixtures.

Pushed 21faad6d1 (fix(ts-checker): align tagged template overload resolution).

• Distinguishes compiler-synthesized TemplateStringsArray arguments from ordinary array literals, preserving TS2741 for the missing raw property.
• Reports TS2554 when ordinary/tagged calls exceed the complete visible overload boundary.
• Flipped both taggedTemplateStringsWithOverloadResolution1{,_ES6} exact tsgo fixtures: 2/2 exact.
• 4000-4999 partition advances 983 -> 985/1000; leading 0-4999 advances 4,871 -> 4,873/5,000.
• Full checker suite: 3,803/3,803.

Pushed 05eeff9f2 (fix(ts-checker): align tagged generic overload diagnostics).

• Enforces inferred generic constraints during overload applicability instead of leaking post-selection TS2345 diagnostics.
• Reports TS2769 from the last arity-compatible overload, including the constraint child and related declaration.
• Adds primitive String legacy members to spelling suggestions without changing structural assignability.
• Flipped both taggedTemplateStringsWithOverloadResolution3{,_ES6} exact tsgo fixtures: 2/2 exact.
• 4000-4999 partition advances 985 -> 987/1000; leading 0-4999 advances 4,873 -> 4,875/5,000.
• Full checker suite: 3,805/3,805.

Pushed 5f4d184b3 (fix(ts-checker): align tagged template type inference).

Parity movement:

• Flipped 2 exact tsgo fixtures: taggedTemplateStringsTypeArgumentInference and its ES6 variant.
• Partition 4000-4999: 987/1000 -> 989/1000.
• Leading exact parity: 4,875/5,000 -> 4,877/5,000.
• Checker suite: 3,806/3,806 passing.

Implemented repeated generic candidate behavior for tagged templates: widened scalar return inference with literal-only argument diagnostics, mutable object/nullish best-common unions, equivalent-object collapse, explicit any dominance without treating empty-array inference as explicit any, and cleanup of provisional contextual callback diagnostics after successful inference.

Pushed 42062aaf8 (fix(ts-checker): align virtual default export merging).

Parity movement:

• Flipped multipleDefaultExports01 exact against current tsgo.
• Partition 4000-4999: 989/1000 -> 990/1000.
• Leading exact parity: 4,877/5,000 -> 4,878/5,000.
• Canonical fixture: 1/1 passing.
• Default-export checker cluster: 24/24 passing.

Implemented order-independent class/function default-export merging per virtual file section, retained all three TS2528 conflicts when a value default joins the merge, deferred merge diagnostics to preserve tsgo ordering, and anchored identifier default exports on the identifier span.

Pushed 8c27e587b (fix(ts-checker): align constructor signature comparisons) directly to main as Chris, with no coauthors.

This ports tsgo's whole-signature constructor comparability behavior: concrete constructor parameters must relate in one consistent direction, while generic constructors and ordinary zero-required-argument overlap remain comparable. It also fixes rest-constructor rendering in TS2365/TS2367 so { new (...a: T[]): R } prints as new (...a: T[]) => R.

Parity impact:

• comparisonOperatorWithSubtypeObjectOnConstructorSignature: exact pass
• comparisonOperatorWithNoRelationshipObjectsOnConstructorSignature: exact pass
• shard 4,000-4,999: 990/1,000 -> 992/1,000
• leading 5,000: 4,878 -> 4,880 exact passes
• added 1 focused checker regression covering 6 comparison shapes

Verification:

• focused checker regression: pass
• canonical exact filter OnConstructorSignature: 2/2
• git diff --check: pass

Next cluster: typeAssertions + constAssertions.

Pushed 085539d7b (fix(ts-checker): complete const assertion diagnostics) directly to main as Chris, with no coauthors.

This completes current tsgo constAssertions behavior across four areas: const-asserted object properties are readonly inside their own methods, parenthesized invalid operands keep the opening-parenthesis TS1355 anchor, asserted object assignment failures elaborate at the mismatched property, and TS1355 uses the current singular wording in both checker emissions and the diagnostic catalog.

Parity impact:

• constAssertions: exact pass
• shard 4,000-4,999: 992/1,000 -> 993/1,000
• leading 5,000: 4,880 -> 4,881 exact passes
• added 1 focused checker regression covering 3 repaired diagnostic surfaces

Verification:

• focused TS1355 regression: pass
• focused const semantic regression: pass
• canonical exact filter constAssertions: 1/1
• git diff --check: pass

Continuing with the remaining typeAssertions fixture in the assertion cluster.

Pushed 1594b5edf (fix(ts-parser): preserve type assertion recovery) to main as Chris, with no coauthor trailers.

Parity movement:

• Flipped canonical typeAssertions from failing to exact pass.
• typeAssertions filtered group: 3/3 exact.
• Exact shard 4000-4999: 993 -> 994 / 1000.
• Leading exact corpus 0-4999: 4,881 -> 4,882 / 5,000.

Implementation:

• Preserved the parsed source root through malformed predicate-like assertion tails, restoring all earlier binder/checker diagnostics.
• Matched tsgo TS1434/TS1128 recovery ordering for (expr as value is string).
• Ported tsgo binary + result behavior so one any operand remains any after concrete string/number checks, removing the spurious TS2403.
• Added 1 parser and 2 checker regressions.

Verification:

• Canonical exact typeAssertions filter: 3 passed, 0 failed.
• Focused checker regressions: pass.
• Parser suite: 849/850; only the tracked pre-existing TS8009 diagnostic-count mismatch remains.

Pushed 869c8b123 (fix(ts-checker): propagate contextual callable types) to main as Chris.

This chunk flips 3 exact tsgo fixtures by porting contextual callable propagation through overload arity selection, inherited super construct signatures, conditional/comma wrappers, nested returns, and typed object-literal arrows.

Parity movement:

• 4000-4999: 994/1000 -> 997/1000
• leading 0-4999: 4,882/5,000 -> 4,885/5,000

Exact verification:

• parenthesizedContexualTyping2: 1/1
• ContextualTyping2 filter: 3/3 (including superCallParameterContextualTyping2)
• generatedContextualTyping: 1/1
• 5 focused checker regressions pass

Remaining in the shard: incrementAndDecrement, commaOperatorWithSecondOperandObjectType, and typeOfThisGeneral.

Pushed two small parity chunks to main as Chris (no coauthors):

• 48fa953ec fix(ts-parser): align operator statement recovery (+37): rejects update-expression assignment at =, honors ASI before postfix !, and restores 2 recovered-object TS8009 diagnostics. This flips commaOperatorWithSecondOperandObjectType, supplies the parser half of incrementAndDecrement, and leaves the parser suite at 852/852.
• 9f6464c8f fix(ts-checker): complete operator and this parity (+186/-22): assigns contextual-return diagnostics to the correct expression owner, distinguishes bare window TS2304 from member TS2812 under explicit non-DOM libs, honors @strict: false for constructor/globalThis checks, and merges polymorphic-this default parameters with hoisted body var declarations while preserving generic TS2403 text.

Exact results:

• formerly failing quartet: 4/4 exact
• contextual/operator/this regression batch: 7/7 exact
• exact corpus shard 4,000-4,999: 1,000/1,000 (up from 996/1,000 before this batch; parser commit moved it to 997, checker commit completed the final 3)

The canonical tsgo submodule remains configured at _submodules/typescript-go, branch = main, pinned to 24fabe95acba758c05fcb349bf427a3a0c8ad676.

A full checker-unit sweep also identified the next seven-test follow-up queue (predicate this positions, contextual object-union ownership, undefined as this, generic callback inference, two JSDoc contextual-flow cases, and non-array .map spread typing). Those are unit-level parity gaps outside this now-green exact shard and are the next batch.

Pushed three checker parity commits to main as Chris (no co-authors):

• cc59ccd52 fix(ts-checker): align callable relation ownership - closed 3 focused regressions around explicit-this predicate callbacks, contextual object-union method return ownership, and assertions to polymorphic this.
• 2cc7800b3 fix(ts-checker): preserve generic instantiation boundaries - closed the qualified typeof node.member<any> inference boundary regression.
• 13c4de62c fix(ts-checker): close 3 contextual typing gaps - 82 insertions / 20 deletions closing inline JSDoc @satisfies ownership, chained dotted-optional JSDoc TS18048 reporting, and non-array .map callback ownership.

Verification on the pushed tree:

• full ts_checker suite: pass
• parser suite remains 852/852 from 48fa953ec
• exact conformance shard 4000-4999 remains 1000/1000 from 9f6464c8f
• affected exact conformance fixtures: 4/4 (spreadNonObject1, checkJsdocSatisfiesTag3, both jsDeclarationsOptionalTypeLiteralProps variants)
• affected exact compiler fixture: 1/1 (symbolToNodeBoundaryNoStackOverflow)

This closes all seven checker unit gaps isolated from the last full checker run with semantic implementations rather than harness exceptions.

TS parity checkpoint: scanner recovery batch

Pushed 40b9a10e0 (fix(ts-parser): recover escaped keywords and null bytes) to main as Chris Breuer with no coauthor trailers.

• Flipped 2 exact conformance fixtures: scannerUnicodeEscapeInKeyword2 and scannerUnexpectedNullCharacter1.
• Preserved binary expressions across embedded NUL scanner tokens while retaining both canonical TS1127 diagnostics.
• Restricted TS1260 ownership to true keyword positions; escaped await/yield bindings, type-alias names, and object keys remain legal IdentifierNames.
• Matched all 7 canonical TS1260 diagnostics across the two virtual escaped-keyword files.
• Change size: 72 insertions, 6 deletions in packages/ts_parser/src/ts_parser.zig.

Verification:

• Parser suite: 854/854 passed.
• Focused exact conformance: 2/2 passed.
• Fresh measured full baseline before this batch: 5,624/5,907 (95.21%), 283 failures.
• Inferred dashboard after these exact flips: 5,626/5,907 (95.25%), 281 failures. A later full exact sweep will remeasure this directly.

TS parity checkpoint: inline JSX scope batch

Pushed ef0506f16 (fix(ts-checker): scope inline JSX factories per file) to main as Chris Breuer with no coauthor trailers.

• Flipped 2 exact fixtures: inlineJsxAndJsxFragPragma and inlineJsxFactoryWithFragmentIsError.
• Kept inlineJsxAndJsxFragPragmaOverridesCompilerOptions green in the same focused exact run.
• Scoped @jsx / @jsxFrag parsing and factory lookup to each virtual file.
• Counted classic JSX factory and fragment imports as reads for noUnusedLocals.
• Prevented renderer declarations from leaking into sibling virtual-file scope.
• Exposed declare global { namespace JSX { ... } } to intrinsic lookup.
• Reported both classic fragment aliases while preserving TS17017 and TS2879 ownership.
• Change size: 141 insertions, 27 deletions in packages/ts_checker/src/check.zig.

Verification:

• Complete checker suite passed.
• Focused checker regression passed.
• Focused exact conformance: 3/3 passed.
• Inferred dashboard after this batch: 5,628/5,907 (95.28%), 279 failures. A later full exact sweep will remeasure directly.

TS parity checkpoint: JSX recovery and value semantics

Pushed two small conventional commits to main as Chris Breuer with no coauthor trailers:

• 6654d3366 fix(ts-parser): stop malformed fragment sibling recovery
  • Flipped tsxFragmentErrors.
  • Stops TS2657 sibling recovery at a new line after malformed-fragment TS17014/TS17015 recovery.
  • Change size: 21 insertions.
• 1563c89fb fix(ts-checker): align JSX tags and comma side effects
  • Flipped tsxDynamicTagName9 and tsxEmit3.
  • Treats literal-valued dynamic tags as intrinsic when no IntrinsicElements declaration exists.
  • Treats member/element access as observably effectful comma operands, matching tsgo isSideEffectFree ownership.
  • Change size: 27 insertions, 1 deletion.

Verification:

• Parser suite: 855/855 passed.
• Complete checker suite passed.
• Focused exact conformance: 3/3 passed.
• Inferred dashboard after these 3 flips: 5,631/5,907 (95.33%), 276 failures. A later full exact sweep will remeasure directly.

TS parity checkpoint: JSX option-matrix ownership

Pushed 3784a7e30 (fix(ts-driver): separate JSX option matrices from pragmas) to main as Chris Breuer with no coauthor trailers.

• Flipped jsxAttributeInitializer.
• Prevented comma-separated // @jsx compiler-option matrices from being treated as inline custom JSX factory pragmas.
• Preserved TS17017 for real block-comment @jsx pragmas without @jsxFrag.
• Change size: 16 insertions, 1 deletion in packages/ts_driver/src/ts_driver.zig.

Verification:

• Complete driver suite passed.
• Focused exact conformance: 1/1 passed.
• Inferred dashboard: 5,632/5,907 (95.35%), 275 failures. A later full exact sweep will remeasure directly.

TS parity checkpoint: JSX scanner and close recovery

Pushed 929be2243 (fix(ts-parser): align JSX text and closing recovery) to main as Chris Breuer with no coauthor trailers.

• Flipped jsxParsingError2, jsxParsingError3, and jsxParsingErrorImmediateSpreadInAttributeValue.
• Ported tsgo parent-closing-tag reattachment so an unclosed nested JSX child leaves its parent close available.
• Restored the single root EOF TS1005: </ expected diagnostic.
• Split adjacent greater tokens at the JSX opening/text boundary and removed duplicate internal stray-text diagnostics.
• Change size: 94 insertions, 8 deletions in packages/ts_parser/src/ts_parser.zig.

Verification:

• Complete parser suite: 858/858 passed.
• Focused exact jsxParsingError* family: 5/5 passed.
• Inferred dashboard: 5,635/5,907 (95.40%), 272 failures. A later full exact sweep will remeasure directly.