[Repo Assist] Fix FSharp.workspacePath resolution in multi-folder workspaces

[github-actions]

🤖 This PR was created by Repo Assist, an automated AI assistant.

Closes #1976

---

Root Cause

When a user sets FSharp.workspacePath to a relative path (e.g. "backend/App.sln") in a multi-folder VS Code workspace, Ionide resolved the path exclusively against workspace.rootPath — which is always the first workspace folder. If the F# project lives in a folder that isn't first in the list, the resolved path does not exist, Ionide silently ignores the setting, and no solution/directory is loaded.

Additionally, workspace.rootPath.Value would crash with a null-reference exception when no workspace folder is open at all.

Minimal repro: workspace with folders ["client", "dotnet"] and FSharp.workspacePath = "dotnet/App.sln" → resolved as (client-path)/dotnet/App.sln (wrong folder) → path does not exist → ignored.

Fix

• Rename parse → parseWithBase to accept an explicit base path rather than implicitly reading workspace.rootPath.Value.
• Add candidateBasePaths() which returns rootPath :: workspaceFolders (deduped) — all possible base paths in the workspace.
• In parseAndValidate, try each candidate path in order, returning the first one that physically exists on disk. If none exist, warn and return None (same as before).

Behaviour Changes

Scenario	Before	After
Single-folder, relative path	✅ Works	✅ Works (unchanged)
Multi-folder, path in first folder	✅ Works	✅ Works (unchanged)
Multi-folder, path in non-first folder	❌ Silently ignored	✅ Resolved correctly
Absolute path	✅ Works	✅ Works (unchanged)
No workspace open (rootPath = None)	💥 Exception	✅ Falls back to workspaceFolders

Trade-offs

• Tries multiple paths instead of one — negligible overhead (a few stat syscalls at startup/configuration-change time only).
• If two workspace folders both contain a relative path like "src/App.sln", the one in rootPath/first folder wins (consistent with existing priority ordering).

Test Status

Fable compilation: ✅ No errors (dotnet fable src --noCache — 0 error FSHARP lines, only pre-existing deprecation warnings unrelated to this change).

No existing automated test suite covers this integration path (workspace configuration resolution uses VS Code's live API, not unit-testable in isolation).

Generated by Repo Assist · ◷

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@346204513ecfa08b81566450d7d599556807389f