Add Visual Studio 2026 (GitHub Copilot in VS) as a harness #283

Problem

AI Engineer Coach reads sessions from VS Code (Copilot Chat), GitHub Copilot App/CLI (~/.copilot/session-state), Xcode, and the external harnesses Claude Code, Codex CLI and OpenCode (src/core/parser-harnesses.ts). There is no collector for Visual Studio 2026 (18.x).

Developers using GitHub Copilot Chat / agent mode inside Visual Studio (.NET, C++ shops) therefore get no Timeline, Output, Patterns or Anti-Patterns coverage for that work — even though the extension (or the Copilot app canvas) runs on the same Windows machine and the session data already exists locally. Since the April 2026 update, Visual Studio keeps a dedicated chat history panel (titles, message previews, timestamps), so the sessions are persisted and parseable.

Related: #151 (additional harnesses on hold). Xcode support shows the project already accepts non-VS Code IDEs as first-class harnesses, which is the precedent for this request.

Proposed Solution

1. New collector Visual Studio in src/core/parser-harnesses.ts, backed by src/core/parser-visualstudio.ts following the parser-claude / parser-codex / parser-opencode pattern: findVisualStudioDirs() + parseVisualStudioSessions(dir, editLocIndex). Add 'VisualStudio' to EXTERNAL_HARNESS_SET.
2. Discovery, Windows only (process.platform === 'win32'):
   • primary: the VS 2026 persisted chat-session store (undocumented; expected under %LOCALAPPDATA%\Microsoft\VisualStudio\18.0_<instance>\ — path and schema to confirm, I can provide anonymised samples);
   • fallback: %LOCALAPPDATA%\Temp\**\*VSGitHubCopilot.chat.log — the format VS 2022 used (system prompt, analysed context, user/assistant turns). See https://github.com/orgs/community/discussions/57190#discussioncomment-11536706.
3. Mapping to Session:
   • workspace = solution (.sln / .slnx) or project folder found in the log context;
   • user / assistant turns → requests/responses with timestamps;
   • model id → model usage table;
   • agent-mode tool calls (e.g. get_symbol_call_hierarchy, Debugger agent) → tool-mastery metrics;
   • generated code blocks → EditLocIndex (code output by language).
4. Harness label Visual Studio in the sidebar/harness breakdown, distinct from VS Code.
5. hasExternalHarnessSources() returns true when VS logs exist, so the dashboard opens on a machine with no VS Code workspace storage (same reasoning as fix: load dashboard when only non-VS Code harness logs exist (Claude/Codex/OpenCode) #53).
6. Fail soft: skip unparsable files and surface a count through the harness progress handlers, since the VS log format is undocumented and may change between updates.

I'm happy to contribute this as a PR (parser + sample logs + tests) rather than ask the maintainers to build it.

Alternatives Considered

• Use Copilot CLI from the Visual Studio terminal — works today and lands in the GitHub Copilot CLI harness, but misses the IDE chat/agent sessions, which is where most VS users work.
• Export each VS chat manually (copy as Markdown) and convert to the VS Code chatSessions JSON format — no stable export format from VS, and not sustainable day to day.
• Keep a separate fork with the parser — fragments the "any harness, one dashboard" promise and loses the shared rule set.
• Wait for Microsoft to document the VS session store — no public timeline; a tolerant parser with a Temp-log fallback is useful now.