[repo-assist] perf: string/int fast-paths in toParam; StringBuilder+String.Concat in buildXmlDoc

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Summary

Two targeted performance improvements identified during routine codebase analysis.

1. RuntimeHelpers.toParam — fast-path arms for common scalar types

toParam is called for every query parameter, path parameter, and header value in every generated API client call. Previously, all types except DateTime and DateTimeOffset fell into the catch-all _ -> branch, which:

1. Calls obj.GetType()
2. Compares ty.FullName to dateOnlyTypeName
3. Compares ty.FullName to timeOnlyTypeName
4. Checks ty.IsGenericType
5. Checks ty.IsEnum
6. Finally calls obj.ToString()

For the most common OpenAPI scalar types — string, int32, int64, and bool — all five checks are wasted work.

Fix: add explicit match arms for these four types, short-circuiting directly to the result:

| :? string as s -> s
| :? int32 as i -> i.ToString()
| :? int64 as i -> i.ToString()
| :? bool as b -> b.ToString()

This avoids GetType() plus four branch evaluations per call for any parameter of these types.

2. Utils.buildXmlDoc — StringBuilder + String.Concat with 4 args

buildXmlDoc is called once per compiled operation at design time. Two minor allocations reduced:

• paramParts: replaced [ for ... do yield ... ] |> String.concat "" (builds an F# cons-cell list then concatenates) with a StringBuilder loop — no intermediate list allocation.
• Final join: replaced summaryPart + remarksPart + paramParts + returnsPart (two intermediate strings due to left-associative +) with String.Concat(summaryPart, remarksPart, paramParts, returnsPart) — single allocation.

Test Status

✅ All 417 unit tests pass
✅ Build succeeds (0 errors, warnings pre-existing)
✅ Fantomas format check passes

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[Copilot]

Pull request overview

Two micro-optimizations: a fast path in RuntimeHelpers.toParam for the most common scalar types (string/int32/int64/bool) to avoid reflection, and a StringBuilder/String.Concat rewrite of Utils.buildXmlDoc to reduce intermediate allocations.

Changes:

• Add fast-path match arms for string, int32, int64, bool in toParam before the reflective fallback.
• Replace list comprehension + String.concat "" with StringBuilder for assembling <param> parts in buildXmlDoc.
• Replace chained + join of XML doc parts with String.Concat 4-arg overload.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/SwaggerProvider.Runtime/RuntimeHelpers.fs	Adds scalar-type fast paths in toParam matching prior semantics (uses ToString() like previous fallback).
src/SwaggerProvider.DesignTime/Utils.fs	Rewrites paramParts building with StringBuilder and joins final parts via String.Concat.

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