Add C# as a supported output language

[jarsh921]

Follows the exact same pattern as python/javascript/typescript:

• New prompt partial (prompts/partials/_language_csharp.md): uses System.Net.Http.HttpClient and System.Text.Json - both part of the .NET 5+ base class library, so no NuGet package is needed for HTTP or JSON (unlike Java, .NET's stdlib does include JSON support). Packaged as a minimal .csproj so dotnet run just works. Same auth-hardcoding/refresh guidance as the other languages. No filename vs. class-name naming workaround needed here (unlike Java) - C# doesn't require a public class's name to match its file's name.
• base_engineer.py: added "csharp" to _OUTPUT_LANGUAGE_EXTENSIONS (.cs), _get_language_name() ("C#"), _get_run_command() ("dotnet run"), and _get_auto_output_files() (ApiClient.csproj, always included - a project file is required to dotnet run regardless of dependencies, matching typescript's "always" precedent rather than javascript/go's conditional one).
• cli.py: added C# to the interactive output_language config picker.
• Updated the three docstrings/comments that listed the language set (config.py, engineer.py, prompts/init.py) and README.md's output language line.
• Tests: mirrored the existing per-language test pattern in test_base_engineer.py (extension, run command, prompt content) and test_prompts.py (partial loading) for C#.

Checked the partial for the literal-brace str.format_map() bug caught in the Java PR before writing this one - no literal {/} anywhere in the new file (confirmed via grep), since C# code snippets weren't needed to convey the guidance here.

Full test suite passes (49/49, run 3x) except the same pre-existing flaky test as the other language PRs
(test_existing_client_language_falls_back_to_newest_file - a mtime-resolution race condition, unrelated to this change, present on a clean main checkout too). ruff check is clean on every file this touches (8 pre-existing lint errors elsewhere on main, none in the touched lines).

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Summary by cubic

Adds C# as a supported output language that generates a minimal .NET project and runs with a cwd‑independent dotnet run --project command. The run command resolves and shell‑quotes the project path so it works from any directory, including paths with shell metacharacters.

• New Features

  • base_engineer: maps csharp -> .cs, language "C#", run command dotnet run --project {scripts_dir}/ApiClient.csproj using shlex.quote and an absolute path, and always includes ApiClient.csproj.
  • New partial prompts/partials/_language_csharp.md using HttpClient/System.Text.Json (available since .NET Core 3.0), with auth hardcoding/refresh, save paths, and adaptive target framework guidance (default net8.0; adjust up or down to match the installed SDK).
  • CLI adds csharp; README/config/engineer/prompt docs updated.

• Tests

  • tests/test_base_engineer.py: asserts .cs extension; run command points to a resolved, safely quoted project path; handles metacharacters; resolves relative output dirs; C# prompt content included.
  • tests/test_prompts.py: verifies the C# partial loads and renders run_command and paths.

^{Written for commit 6306e39. Summary will update on new commits.}

Greptile Summary

This PR adds C# as a supported output language. The main changes are:

• C# prompt guidance using the .NET base class library.
• .cs and .csproj output handling.
• An absolute, shell-quoted dotnet run --project command.
• C# support in settings, documentation, and tests.

Confidence Score: 5/5

This looks safe to merge.

• The run command now points directly to the generated project from any working directory.
• The target-framework guidance now handles installed SDK and runtime differences.
• No blocking issues were found in the updated code.

Important Files Changed

Filename	Overview
src/reverse_api/base_engineer.py	Adds C# mappings, project output guidance, and a cwd-independent run command.
src/reverse_api/prompts/partials/_language_csharp.md	Adds C# generation, authentication, project setup, and target-framework guidance.
src/reverse_api/cli.py	Adds C# to the interactive output-language setting.
tests/test_base_engineer.py	Adds coverage for C# extensions, prompts, project paths, and shell quoting.
tests/test_prompts.py	Adds coverage for loading and rendering the C# prompt partial.

_{Reviews (2): Last reviewed commit: "Make the C# target-framework guidance di..." | Re-trigger Greptile}

[cubic-dev-ai]

No issues found across 10 files

_{Re-trigger cubic}

[kind-agent]

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[cubic-dev-ai]

All reported issues were addressed across 3 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

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[kalil0321]

@greptile review