Fix: CT parameter name uniqueness in CancellationToken overload generation

[Copilot]

If an OpenAPI spec defines a parameter named cancellationToken, the generated overload would emit two parameters with the same name — one from the spec and one for the injected CancellationToken.

Changes

• Track used parameter names: The parameter-fold now returns the usedNames set alongside providedParameters instead of discarding it with |> snd
• Unique CT parameter naming: The injected CT parameter resolves to the first unused name in the sequence cancellationToken → cancellationToken1 → cancellationToken2 → …, matching the existing UniqueNameGenerator convention
• Position-based extraction unaffected: invokeCode already extracts the CT argument by position (last in args), so it correctly handles the CT regardless of the name chosen

let usedNames, providedParameters =
    ((Set.empty, []), orderedParameters)
    ||> List.fold(fun (names, parameters) current -> ...)
    |> fun (names, ps) -> names, List.rev ps

let ctParamName =
    Seq.initInfinite(fun i -> if i = 0 then "cancellationToken" else $"cancellationToken{i}")
    |> Seq.find(fun n -> not(Set.contains n usedNames))

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[Copilot]

Pull request overview

Fixes a codegen edge case in the v3 OpenAPI client type provider where injecting a CancellationToken overload could produce duplicate parameter names when the OpenAPI spec already defines a cancellationToken parameter.

Changes:

• Preserve the usedNames set from the OpenAPI parameter fold instead of discarding it.
• Generate a unique injected CT parameter name (cancellationToken, cancellationToken1, cancellationToken2, …) that avoids collisions with OpenAPI parameters.
• Keep CancellationToken extraction position-based in invokeCode (so behavior doesn’t depend on the chosen parameter name).

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[Copilot]

Add a regression test for the name-collision scenario this change fixes (an OpenAPI parameter named cancellationToken). Without a test that loads/generates a client from such a spec and asserts the generated overload compiles (and/or that the injected CT param gets a suffixed name), this could regress unnoticed.

[Copilot]

This introduces a second ad-hoc unique-name generator (Seq.initInfinite + Set.contains) even though the codebase already has UniqueNameGenerator with the same suffixing convention (and case-insensitive uniqueness). Consider factoring this into a shared helper (or reusing UniqueNameGenerator by seeding it with usedNames) to avoid future divergence in how “unique names” are defined.

Suggested change

	// conflict with any OpenAPI parameter already in use.
	let ctParamName =
	Seq.initInfinite(fun i ->
	if i = 0 then
	"cancellationToken"
	else
	$"cancellationToken{i}")
	|> Seq.find(fun n -> not(Set.contains n usedNames))
	// conflict with any OpenAPI parameter already in use, using the shared
	// UniqueNameGenerator to keep suffixing and case sensitivity consistent.
	let nameGen = UniqueNameGenerator()
	usedNames |> Set.iter (fun n -> nameGen.Claim n |> ignore)
	let ctParamName = nameGen.Claim "cancellationToken"