chore(release): v0.20.3

[Aaronontheweb]

Summary

• Update RELEASE_NOTES.md with v0.20.3 entry (KV cache stability overhaul, vLLM compatibility, OpenAPI support, MCP tool-name robustness, Copilot OAuth restore, and CodeQL security fixes)
• Run build.ps1 to propagate version 0.20.3 and the release notes into Directory.Build.props

What's in this release

Features

• OpenAPI support for the HTTP API (Add openapi support #1146)
• Aspire end-to-end demo (Mattermost + Ollama + daemon) (feat(demo): Aspire end-to-end demo (Mattermost + Ollama + daemon) #1135)

KV Cache Improvements

• Major KV cache hit-rate improvements across llama.cpp, vLLM, and OpenAI-compatible backends (~94% for simple sessions, up from ~75%) (fix(providers): preserve trailing volatile system message for KV cache stability #1171, fix(kv-cache): close residual prefix-invalidation paths after PR #1171 #1174, fix(sessions): persist volatile context into history for cross-turn cache stability #1178)
• vLLM system-message placement compatibility — volatile context now embedded in last User message to satisfy strict chat templates (fix(providers): wrap volatile context in last user message for vLLM compat #1176)
• SetSystemPrompt is now idempotent to avoid mid-session prefix rebuilds (fix(kv-cache): close residual prefix-invalidation paths after PR #1171 #1174)

Bug Fixes

• vLLM modality auto-detection at daemon startup (fix(providers): vLLM modality auto-detection at daemon startup (#987) #1158)
• Copilot OAuth exchange restored; LLM failure detail surfaced to users (fix(copilot): restore OAuth exchange + surface LLM failure detail #1159)
• Approval controls remain visible for long shell prompts in netclaw chat (fix(tui): keep approval controls visible for long prompts (#1132) #1156)
• Normal chat no longer consumed by stale cold-approval path (fix(channels): prevent cold approval path from swallowing normal chat (#1164) #1165)
• MCP tool-name forms (canonical and LLM-facing alias) accepted in config, CLI, and doctor (fix(mcp): accept either tool-name form in config, CLI, and doctor #1154)

Security

• Four CodeQL code-scanning alerts resolved: workflow permissions, log-injection, path traversal (fix(security): address open CodeQL code-scanning alerts #1152)

Dependency Updates

• Mattermost.NET bumped to 5.0; hand-rolled HTTP bypass shim removed (refactor(mattermost): bump Mattermost.NET to 5.0 and delete HTTP-bypass shim #1163)

Test plan

• CI passes all status checks
• Directory.Build.props VersionPrefix is 0.20.3
• RELEASE_NOTES.md top entry is #### 0.20.3 2026-05-26 ####