Rebuild provider-agnostic Microsoft.Extensions.AI gateway sample

[balajibashyam]

Summary

Replaces the existing minimal provider-gateway companion with the verified .NET 10
sample for the
Microsoft.Extensions.AI Tutorial: Build a Multi-Provider IChatClient Gateway.

The existing GitHub path is preserved:

dotnet-ai/provider-agnostic-chat-gateway/

What's included

• Rebuilt sample

  • ASP.NET Core Minimal API
  • Microsoft.Extensions.AI.IChatClient provider boundary
  • allow-listed provider registration
  • Ollama, OpenAI, OpenRouter/OpenAI-compatible, and Azure OpenAI construction paths
  • bounded in-memory conversation state
  • provider-bound conversations
  • non-streaming chat
  • SSE streaming
  • deterministic convert_temperature function tool
  • explicit tool-invocation logging
  • 25 deterministic tests

• Verification

  • .NET SDK 10.0.401
  • net10.0
  • Release build passed
  • deterministic tests passed: 25/25
  • local Ollama live verification completed with qwen3.8:27b
  • non-streaming chat verified
  • conversation continuity verified
  • SSE streaming verified
  • real tool invocation verified
  • unregistered-provider HTTP rejection verified

• Root README

  • existing sample row updated
  • run commands updated
  • repository structure updated

• GitHub Actions

  • existing build-chat-gateway job updated for the new .slnx
  • deterministic tests added to CI
  • no live model or provider credential required

Package baseline

• Microsoft.Extensions.AI 10.10.0
• Microsoft.Extensions.AI.OpenAI 10.10.1
• Azure.AI.OpenAI 2.1.0
• Azure.Identity 1.21.0
• OllamaSharp 5.4.30

Deliberately omitted

• Agent Framework
• MCP
• RAG/vector search
• persistent conversation storage
• automatic failover/load balancing
• model ranking
• multi-agent orchestration
• arbitrary caller-supplied endpoints
• write-capable business tools
• production authentication/deployment

Security boundary

HTTP callers can select only server-registered provider names. Provider endpoints,
models, and credentials remain trusted server configuration.

Independence

This is an independent educational sample and is not an official Microsoft sample
or specification.