docs: salvage F# agent and language guidance

rules/fsharp/hooks.md

@@ -0,0 +1,26 @@
+---
+paths:
+  - "**/*.fs"
+  - "**/*.fsx"
+  - "**/*.fsproj"
+  - "**/*.sln"
+  - "**/*.slnx"
+  - "**/Directory.Build.props"
+  - "**/Directory.Build.targets"
+---
+# F# Hooks
+
+> This file extends [common/hooks.md](../common/hooks.md) with F#-specific content.
+
+## PostToolUse Hooks
+
+Configure in `~/.claude/settings.json`:
+
+- **fantomas**: Auto-format edited F# files
+- **dotnet build**: Verify the solution or project still compiles after edits
+- **dotnet test --no-build**: Re-run the nearest relevant test project after behavior changes
+
+## Stop Hooks
+
+- Run a final `dotnet build` before ending a session with broad F# changes
+- Warn on modified `appsettings*.json` files so secrets do not get committed