Update spec: new settings object, PowerShell cmdlets, fix settings interaction

- Replace extended disableInstallNotes with new userMessages settings object
- Add PowerShell cmdlet section (Install/Update/Uninstall/Repair-WinGetPackage)
- Fix flow matrix to reflect independent settings controls
- Add Show-WinGetPackage output details

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: denelon

doc/specs/#3483 - UserMessages.md

@@ -155,7 +155,9 @@ Post-action messages are displayed in both interactive and non-interactive modes
 | `winget import` | Each package's `Pre*` shown, prompt Y/n per package | Each package's `Post*` shown | Follows the same per-package model |
 | WinGet Configuration (DSC) | Displayed in log output, no prompt | Displayed in log output | Configuration is inherently non-interactive |
 | Operation failure | `Pre*` shown before attempt | `Post*` NOT shown | Post-messages only appear on success |
-| `disableInstallNotes` setting enabled | `Pre*` still shown (not affected) | `Post*` suppressed | Pre-messages are operational; post-messages are informational |
+| `disableInstallNotes` setting enabled | `Pre*` still shown (not affected) | `Post*` still shown (controlled by `userMessages` settings, not `disableInstallNotes`) | Legacy setting does not affect new fields |
+| `userMessages.disablePostActionMessages` enabled | `Pre*` still shown | `Post*` suppressed | New setting for new fields |
+| `userMessages.disablePreActionMessages` enabled | `Pre*` suppressed, no prompt | `Post*` still shown | Suppresses both display and prompt |
 
 #### Bulk Operations (`upgrade --all`, `import`)
 
@@ -165,16 +167,32 @@ A future enhancement could aggregate pre-messages and present them as a summary
 
 ### Settings
 
-The existing `installBehavior.disableInstallNotes` setting is extended:
+A new `userMessages` settings object is introduced under the root of the WinGet settings file. The existing `installBehavior.disableInstallNotes` setting is **not modified** and continues to control only the legacy `InstallationNotes` field.
 
-| Setting | Current behavior | New behavior |
-|---------|-----------------|-------------|
-| `disableInstallNotes: true` | Suppresses `InstallationNotes` after install | Suppresses all `Post*` messages (`PostInstall`, `PostUpgrade`, `PostUninstall`) |
-| `disableInstallNotes: false` (default) | Shows `InstallationNotes` after install | Shows all `Post*` messages |
+```json
+{
+    "userMessages": {
+        "disablePreActionMessages": false,
+        "disablePostActionMessages": false
+    }
+}
+```
+
+| Setting | Default | Description |
+|---------|---------|-------------|
+| `userMessages.disablePreActionMessages` | `false` | When `true`, suppresses all pre-action messages (`PreInstall`, `PreUpgrade`, `PreUninstall`) and their associated prompts. The operation proceeds as if the user confirmed. |
+| `userMessages.disablePostActionMessages` | `false` | When `true`, suppresses all post-action messages (`PostInstall`, `PostUpgrade`, `PostUninstall`). |
 
-Pre-action messages are not affected by this setting because they serve an operational purpose (informing users before a potentially impactful action).
+**Interaction with existing settings:**
 
-> **Future consideration:** If community feedback indicates a need, a separate `disablePreActionMessages` setting could be added. This is not included in this specification.
+| `disableInstallNotes` | `userMessages.disablePostActionMessages` | `InstallationNotes` | `UserMessages.Post*` |
+|----------------------|------------------------------------------|---------------------|----------------------|
+| `false` | `false` | Shown | Shown |
+| `true` | `false` | Suppressed | Shown |
+| `false` | `true` | Shown | Suppressed |
+| `true` | `true` | Suppressed | Suppressed |
+
+The two settings are independent. `disableInstallNotes` governs the legacy field; `userMessages.disablePostActionMessages` governs the new fields. This avoids changing the meaning of an existing setting and gives users granular control during the transition period.
 
 ### COM API
 
@@ -200,6 +218,81 @@ interface IPackageUserMessages : IInspectable
 
 COM consumers are responsible for their own interactivity model. The WinGet COM API does not prompt — it returns the data and the consumer decides how to handle it.
 
+### PowerShell Cmdlets
+
+The WinGet PowerShell module cmdlets consume the COM API and must surface `UserMessages` appropriately.
+
+#### Affected Cmdlets
+
+| Cmdlet | Pre-message field | Post-message field |
+|--------|-------------------|-------------------|
+| `Install-WinGetPackage` | `PreInstall` | `PostInstall` |
+| `Update-WinGetPackage` | `PreUpgrade` | `PostUpgrade` |
+| `Uninstall-WinGetPackage` | `PreUninstall` | `PostUninstall` |
+| `Repair-WinGetPackage` | `PreInstall` (reuses install messages) | `PostInstall` (reuses install messages) |
+
+#### Interactive Behavior
+
+When running interactively in a PowerShell session, cmdlets follow the same pattern as the CLI:
+
+```powershell
+PS> Install-WinGetPackage -Id Publisher.ExampleApp
+
+The following information has been provided by the package publisher:
+
+  This package requires 2 GB of disk space and will modify your PATH.
+
+Do you wish to continue?
+[Y] Yes  [N] No  (default is "Y"):
+```
+
+The prompt uses `$Host.UI.PromptForChoice` (or equivalent) to integrate with PowerShell's native prompting, supporting `-Confirm` and `-WhatIf` patterns where applicable.
+
+#### Non-Interactive / Pipeline Behavior
+
+When running non-interactively (e.g., in a script with no host, or when the user passes `-Force`), pre-action messages are written to the verbose stream (`Write-Verbose`) and the operation proceeds without prompting:
+
+```powershell
+PS> Install-WinGetPackage -Id Publisher.ExampleApp -Force -Verbose
+VERBOSE: Publisher message (PreInstall): This package requires 2 GB of disk space and will modify your PATH.
+```
+
+Post-action messages are written to the information stream (`Write-Information`) so they appear by default but can be suppressed with `-InformationAction SilentlyContinue`.
+
+#### Output Object
+
+The result objects returned by cmdlets should include UserMessages in their output when present:
+
+```powershell
+PS> $result = Install-WinGetPackage -Id Publisher.ExampleApp
+PS> $result.UserMessages
+
+PreInstall  : This package requires 2 GB of disk space and will modify your PATH.
+PostInstall : Restart your terminal to use the CLI.
+```
+
+This allows scripts to programmatically inspect messages after an operation:
+
+```powershell
+$result = Install-WinGetPackage -Id Publisher.ExampleApp -Force
+if ($result.UserMessages.PostInstall) {
+    Write-Host "Note from publisher: $($result.UserMessages.PostInstall)" -ForegroundColor Yellow
+}
+```
+
+#### Find-WinGetPackage / Show-WinGetPackage
+
+The `Show-WinGetPackage` (or `Get-WinGetPackage`) cmdlet should include `UserMessages` in its output when displaying package metadata, allowing users to review messages before deciding to install:
+
+```powershell
+PS> Show-WinGetPackage -Id Publisher.ExampleApp | Select-Object -ExpandProperty UserMessages
+
+PreInstall  : This package requires 2 GB of disk space and will modify your PATH.
+PostInstall : Restart your terminal to use the CLI.
+PreUpgrade  : Back up your configuration file before upgrading.
+PostUpgrade : Review the changelog for breaking changes.
+```
+
 ### Validation Pipeline (winget-pkgs)
 
 The `winget validate` command and the automated validation pipeline in the winget-pkgs repository must handle `UserMessages` correctly: