[hood]

Summary

Removes the async callbacks from ResultAsync.map, mapErr and orElse, and reuses the existing Result on skipped branches (also in andThen). Sync callbacks no longer pay for an extra promise and tick; async callbacks are chained only when f returns a thenable.

Closes #688

Results

Node 26, median of 5 runs, esbuild CJS bundle of src/.

Benchmark	Before	After	Gain
11-step Ok chain, microtask ticks	32	12	2.7x
6-step Err chain, microtask ticks	17	7	2.4x
11-step Ok chain, time	1.67µs	0.77µs	2.2x

flowchart LR
  A[then cb] -->|before| B[async fn promise] --> C[await f] --> D[resolve outer]
  A -->|after| E[f sync] --> F[return Ok]

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Notes

• Sync throws inside f still reject the chain (thrown inside .then), same as before.
• orElse now unwraps a returned ResultAsync via _promise, like andThen already does.
• Skipped branches return the same Ok/Err instance instead of a copy.
• All 117 tests, tsc, test types and lint pass.

[changeset-bot]

🦋 Changeset detected

Latest commit: 711d72b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
neverthrow	Patch

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