@@ -0,0 +1,88 @@
+---
+name: interactive-extension-testing
+description: >
+    Guide for setting up the multi-root PowerShell VS Code extension/PSES dev
+    workspace. Use when asked to open the dev workspace, interactively test the
+    extension, set up PSES for F5 debugging, or open pwsh-extension-dev workspace.
+---
+
+# Interactive Extension Testing
+
+Read [.github/copilot-instructions.md](../../../.github/copilot-instructions.md)
+"Build, Lint, and Test" and "PSES and Cross-Repo Work" first — this skill only
+adds the worktree setup details for hands-on F5 testing.
+
+Use this when the goal is to open `pwsh-extension-dev.code-workspace` and run
+**F5 → Launch Extension** against a locally-built PowerShellEditorServices (PSES).
+
+## Prerequisites
+
+- Follow `.github/copilot-instructions.md` for the repository build dependencies and the
+  `modules/` symlink model.
+- Confirm these commands are available: `pwsh`, `dotnet`, `code`, and the PowerShell
+  `InvokeBuild` module.
+- Have a PSES checkout that can be used as `<pses-checkout>`.
+
+## Setup
+
+1. **Build PSES first.** In `<pses-checkout>`, run the PSES build task (for example,
+   `Invoke-Build Build`) so `<pses-checkout>/module/PowerShellEditorServices/bin`
+   exists. Without that directory, the extension `Build` task in
+   `vscode-powershell.build.ps1` asserts `Extension requires PSES`.
+2. **Ensure the workspace can resolve the Server root.** The workspace defines
+   `Client` as `<extension-repo>` and `Server` as `../PowerShellEditorServices`, so a
+   worktree parent may need a sibling link:
+
+    ```sh
+    ln -s <pses-checkout> <extension-repo-parent>/PowerShellEditorServices
+    ```
+
+3. **Ensure the extension can load the runtime PSES module.** `modules/` is gitignored
+   and should point at the built PSES module directory:
+
+    ```sh
+    ln -s <pses-checkout>/module <extension-repo>/modules
+    ```
+
+    In a normal sibling clone, `Invoke-Build RestoreEditorServices` in
+    `vscode-powershell.build.ps1` creates this `modules` link and builds PSES. In a
+    worktree or fresh checkout, create the sibling link first if `Get-EditorServicesPath`
+    cannot resolve `../PowerShellEditorServices/PowerShellEditorServices.build.ps1`.
+
+4. **Open the dev workspace:**
+
+    ```sh
+    cd <extension-repo>
+    code pwsh-extension-dev.code-workspace
+    ```
+
+5. **Launch interactively.** In VS Code, use **F5 → Launch Extension**. The workspace
+   also defines `Launch Extension - Temp Profile`; see `pwsh-extension-dev.code-workspace`
+   for the current launch/task wiring.
+
+## Verify
+
+```sh
+cd <extension-repo>
+readlink modules
+test -d modules/PowerShellEditorServices/bin
+```
+
+Then confirm F5 starts the extension host and attaches to PSES.
+
+## Cleanup
+
+Both links are reversible and not under version control: `modules` is gitignored, and the
+sibling `PowerShellEditorServices` link lives outside `<extension-repo>`. Cleanup is just:
+
+```sh
+rm <extension-repo>/modules
+rm <extension-repo-parent>/PowerShellEditorServices
+```
+
+## How It Resolves
+
+Use `pwsh-extension-dev.code-workspace` as the source of truth for roots and launch
+configs. Use `Get-EditorServicesPath`, `RestoreEditorServices`, and `Build` in
+`vscode-powershell.build.ps1` as the source of truth for how the extension locates,
+links, builds, and asserts the local PSES module.