docs(http-client-csharp): document client method parameter reordering

[JoshLove-msft]

Summary

• Add the missing client-method parameter-ordering scenario to the C# backward-compatibility documentation and table of contents.
• Show how protocol and convenience methods retain their previously published parameter order, including async variants.
• Explain the last-contract requirement, matching constraints, and updates to forwarded arguments and parameter XML documentation.

Documentation only; no generator behavior changes or changelog entry.

Validation

• GitHub Consistency run 36047076718 passed on commit 731fd39cf: Format, Lint, Spell check, Check Changes, and Versions consistency.
• Built the repository's TypeSpec Prettier plugin with Node 24 and pinned pnpm 11.10.0, reproduced the original formatting failure, and ran full pnpm format. The only correction was collapsing the new embedded TypeSpec operation onto one line.
• The changed document passes the configured Prettier check, including the TypeSpec plugin; git diff --check also passed.
• The earlier local restore failure was caused by the older installed pnpm version, not a lockfile defect. No dependency or lockfile changes were needed.
• Local full lint was blocked by incomplete workspace dependencies and a compiler tsconfig error; the GitHub Lint check passed.
• Generator build and unit tests were not run locally because this is a documentation-only change.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@typespec/http-client-csharp@12044

commit: 731fd39

[Copilot]

Copilot review overview

🟢 Approval recommended

Documentation changes were reviewed with no unresolved issues.

Review effort: Lite
Findings: None

What changed in this PR

Documents C# client method parameter reordering for backward compatibility.

Changes:

• Adds the scenario to the table of contents.
• Documents protocol, convenience, and async method ordering.
• Explains matching constraints, argument forwarding, and XML documentation.

File	Description
packages/​http-client-csharp/​generator/​docs/​backward-compatibility.md	Adds parameter-ordering compatibility guidance and examples.

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[github-actions]

No changes needing a change description found.

[Copilot]

Copilot review overview

🔵 Needs a closer look

Address the two requested documentation clarifications before approval.

Review effort: Lite
Findings: None