Add C# Advent of Code automation framework with input fetching, testing, and submission

[Copilot]

Implements a complete automation framework for Advent of Code in C# to eliminate manual input fetching, enable test-driven development, and streamline answer submission.

Core Services

• AoCConfig: Session cookie management via file (.aoc-session), environment variable, or interactive CLI
• AoCClient: HTTP client for AOC API - fetches inputs, submits answers, parses responses (correct/incorrect/rate-limited)
• Enhanced AoCDay: Base class now supports test cases, automatic input fetching with caching, and async submission

CLI Interface

dotnet run --project AoC -- -y 2025 -d 1 -t -s  # Run with tests and submission
dotnet run --project AoC -- --configure         # Setup session cookie

Arguments: -y/--year, -d/--day, -t/--test, -s/--submit, -c/--configure, -h/--help

Solution Template

public class Day01 : AoCDay
{
    public Day01()
    {
        AddTestCase(input: "sample", expectedPart1: "42", expectedPart2: "84");
    }

    public override string? SolvePart1(string[] input) { /* impl */ }
    public override string? SolvePart2(string[] input) { /* impl */ }
}

Test cases validate solutions before running on real input. Input auto-fetches and caches on first run.

Project Updates

• Migrated to .NET 8.0
• Simplified .csproj to use wildcards for input files (Input\**\*.txt)
• Fixed path resolution to use AppDomain.BaseDirectory instead of working directory
• Added .aoc-session to .gitignore

Documentation

• README.md: Complete setup and API reference
• QUICKSTART.md: 5-minute getting started guide
• DayTemplate.cs.template: Copy-paste template for new solutions

Security: CodeQL analysis clean. No credentials in code or version control.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create an Advent of Code 2025 template with automated input fetching, testing, and submission</issue_title>
<issue_description>## Overview
Develop a template/script for Advent of Code 2025 that:

• Automatically fetches the input file for a given problem and day from the Advent of Code website using the user's session cookie.
• Provides an easy-to-use structure or harness for testing solutions locally with provided examples and real input.
• Offers automated solution submission to Advent of Code site, capturing and displaying the result/status.

Features

1. Input Automation
   • Fetch input file for a specific year and day based on user/session info.
   • Store inputs in a local directory for later runs.
2. Testing
   • Integrate simple testing (using built-in asserts or a lightweight test framework) for checking solutions on sample input/output before running on real input.
   • Optionally allow user to provide more test cases.
3. Submission Automation
   • Script to automatically submit answers to Advent of Code and process response, including handling of wrong-right answers, wait times, and reporting result to the user.
4. Documentation & Setup
   • Instructions for configuring the session cookie securely.
   • Example usage to illustrate the workflow, e.g., python solve.py 2025 1 or similar.

Implementation Suggestions

• Choose Python for initial script (or make language-agnostic if practical).
• Separate configuration for session cookie/token to avoid accidental leaks.
• User prompts or CLI arguments for year, day, and part selection.

Benefits

• Saves time fetching/copying input and submitting answers manually.
• Reduces repeated boilerplate for new days/problems.
• Makes testing, development, and submission more reliable and streamlined.

Notes

• Take care to not expose or commit session cookies/tokens.
• Look at advent-of-code-data or AOC session tools for implementation ideas and best practices.

---

This would improve usability, automation, and accelerate the workflow for Advent of Code 2025.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create an Advent of Code 2025 template with automated input fetching, testing, and submission #1

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