Fix reparseTopLevelAwait diagnostic slicing bug

[Copilot]

await { bar: 42 } in a module context produced spurious parse errors because initial-parse diagnostics leaked through the reparse.

Analysis

In reparseTopLevelAwait, the diagnostic range-end search sliced backward from diagnosticStart instead of forward:

// Bug: searches [0, diagnosticStart) — always returns -1
core.FindIndex(savedParseDiagnostics[:diagnosticStart], ...)

// Fix: searches [diagnosticStart, end) — correctly finds range boundary
core.FindIndex(savedParseDiagnostics[diagnosticStart:], ...)

This is a mistranslation of TypeScript's findIndex(array, predicate, startIndex), which searches from startIndex. The -1 result caused the entire tail of initial-parse diagnostics to be copied, including diagnostics for the range being reparsed with await context.

Changes

• internal/parser/parser.go: Fix slice direction in diagnostic range search
• testdata/tests/cases/compiler/awaitObjectLiteral.ts: New test case
• Baseline updates: reachabilityChecksNoCrash1 loses 2 spurious errors (convergence improvement)

Copilot Checklist

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• npx hereby build
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[Copilot]

Pull request overview

Fixes a mistranslation bug in reparseTopLevelAwait where the diagnostic-range end search was slicing the diagnostics list in the wrong direction ([:diagnosticStart] instead of [diagnosticStart:]). The bug caused initial-parse diagnostics covering the awaited region to leak into the reparsed output (since FindIndex on the prefix slice always returned -1, so the entire tail was appended), producing spurious parse errors for code like await { bar: 42 } at the top level of a module. With the fix, diagnosticEnd is correctly interpreted as a relative offset, matching the existing slice math savedParseDiagnostics[diagnosticStart : diagnosticStart+diagnosticEnd].

Changes:

• One-line fix to slice direction in reparseTopLevelAwait diagnostic range search.
• New compiler test awaitObjectLiteral.ts exercising top-level await of an object literal in module context.
• Baseline updates: reachabilityChecksNoCrash1 loses 2 spurious errors (convergence toward TS reference).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/parser/parser.go	Fix slice direction ([diagnosticStart:]) so FindIndex searches forward from the start of the range, returning the correct relative end offset.
testdata/tests/cases/compiler/awaitObjectLiteral.ts	New minimal regression test covering top-level await { ... } across two module files.
testdata/baselines/reference/compiler/awaitObjectLiteral.js	New emit baseline for the new test.
testdata/baselines/reference/compiler/awaitObjectLiteral.symbols	New symbols baseline for the new test.
testdata/baselines/reference/compiler/awaitObjectLiteral.types	New types baseline confirming await { bar: 42 } is typed as { bar: number; }.
testdata/baselines/reference/submodule/compiler/reachabilityChecksNoCrash1.errors.txt	Removes 2 spurious diagnostics (TS1135, TS1128) and updates error count from 37 to 35.
testdata/baselines/reference/submoduleAccepted/compiler/reachabilityChecksNoCrash1.errors.txt.diff	Shrinks the accepted diff vs. the TS reference, reflecting convergence.