Fix Debug task to avoid fragile npm argument forwarding

[ayush-meghwani-28]

Problem

The generated Debug: Excel Desktop VS Code task runs:

npm run start -- desktop --app excel

This relies on npm forwarding the --app option flag across the -- separator. On some npm versions the flag is not forwarded, so the command resolves to:

office-addin-debugging start manifest.xml desktop excel

That passes 3 positional arguments to start (which accepts only <manifest-path> [platform]), producing:

error: too many arguments for 'start'. Expected 2 arguments but got 3.

Because the debug task aborts before the dev server starts, Excel then reports "Add-in ... failed to download a required resource." This was hit by a customer scaffolding an Excel Custom Functions + Shared Runtime project and pressing F5.

Fix

Move the arguments into a dedicated start:desktop npm script so nothing is forwarded through --:

• package.json: add "start:desktop": "office-addin-debugging start manifest.xml desktop --app excel"
• .vscode/tasks.json: Debug: Excel Desktop now runs ["run", "start:desktop"]

This keeps the desktop / --app excel intent, is immune to npm's -- handling, and is backward compatible (identical result on old and new npm). The new script is additive — the existing start script and npm start flow are unchanged.

Verified locally: F5 builds, starts the dev server, and sideloads the add-in into Excel; custom functions execute.

Note on scope

The same npm run start -- <platform> --app <host> pattern exists in the sibling template repos (Excel-Custom-Functions, Excel-Custom-Functions-JS, Excel-Custom-Functions-Shared-JS, and the Office-Addin-TaskPane* / React repos). Starting with this repo since it's the one in the reported issue — happy to mirror the same fix across the others once the approach is confirmed. For the multi-host TaskPane manifests, the --app value must be preserved (it selects which host to launch), which this script-based approach supports.

[azure-pipelines]

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[millerds]

This doesn't scale. In general, the templates support multiple host and it's not practical to have a script command for each host and then have to adjust that when the projects are generated. This is why we use the extended arguments '--' flag. While this repo doesn't have multiple hosts . . . we like to keep the templates in sync for common thing (it's easier to maintain).