fix(rest): SoftPathArgs for widened path inference in RestEndpoint subclasses

[ntucker]

Follows up on #3845.

Motivation

When subclassing RestEndpoint with O extends RestGenerics = any, TypeScript can widen path literals (e.g., '/users') to string during constructor inference. This caused PathArgs<string> to produce a restrictive index-signature type, which in turn created union overloads in ParamFetchWithBody. These unions made getOptimisticResponse, key, url, and process callbacks unassignable — their parameter types didn't match the union of possible argument tuples.

Additionally, endpoints with an explicit body but no method were defaulting to GET, making the body optional instead of required.

Solution

• SoftPathArgs<P> — new utility type in pathTypes.ts that collapses PathArgs<string> to unknown (the identity for &), preventing the problematic union overloads while preserving full inference for literal paths.
• Method inference from body — when body is explicitly provided and not undefined, RestEndpointConstructorOptions and RestEndpoint now infer POST as the default method for OptionsToBodyArgument, making the body required.
• Legacy types — SoftPathArgs added to src-4.0-types/pathTypes.d.ts for TS 4.0 compatibility.
• Comprehensive type tests covering:
  • All Parameters<F>-dependent callbacks (getOptimisticResponse, key, url, process) with widened paths
  • Widened paths with searchParams + body, params + body
  • .extend() on widened-path endpoints
  • resource() with AuthdEndpoint subclass + all extend patterns (per-endpoint, object form, function form)

---

Note

Medium Risk
Type-only changes to RestEndpoint inference could change TypeScript call signatures (e.g., body becoming required when method is omitted), potentially surfacing new compile errors in downstream code, though runtime behavior is unaffected.

Overview
Fixes TypeScript inference for RestEndpoint subclasses where path literals get widened to string, ensuring constructor callbacks like getOptimisticResponse, key, url, and process receive usable parameter types (including when searchParams: undefined is set).

Updates RestEndpoint typing to infer the default method from an explicitly provided body (treating it as POST), so body remains required across .extend() when method was omitted. Adds SoftPathArgs (including TS4.0 d.ts + playground types) and expands TypeScript tests to cover widened paths, subclassing, extend(), and resource() integration. Also fixes incorrect intra-blog links in the v0.15 release post.

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🦋 Changeset detected

Latest commit: 3877777

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

This PR includes changesets to release 4 packages

Name	Type
@data-client/rest	Patch
example-benchmark-react	Patch
test-bundlesize	Patch
coinbase-lite	Patch

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Size Change: 0 B

Total Size: 80.9 kB

ℹ️ View Unchanged

Filename	Size
examples/test-bundlesize/dist/App.js	3.44 kB
examples/test-bundlesize/dist/polyfill.js	307 B
examples/test-bundlesize/dist/rdcClient.js	10.4 kB
examples/test-bundlesize/dist/rdcEndpoint.js	6.35 kB
examples/test-bundlesize/dist/react.js	59.7 kB
examples/test-bundlesize/dist/webpack-runtime.js	726 B

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.08%. Comparing base (9b6c7f4) to head (3877777).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

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##           master    #3847   +/-   ##
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  Coverage   98.08%   98.08%           
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  Files         152      152           
  Lines        2871     2871           
  Branches      563      563           
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  Hits         2816     2816           
  Misses         11       11           
  Partials       44       44           

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