Unable to sideload Unified Manifest due to 429 error

Expected behavior

Expect that running office-addin-debugging start manifest.json command should sideload and start the associated add-in.

Current behavior

Sideloading fails with a 429 error (full error message below). This has been happening for over a week now, all unified manifests are impacted even brand new scaffolded projects.

--Error sideloading!--
Error: Error: Command failed: npx -p @microsoft/m365agentstoolkit-cli atk install --file-path "C:\Users\JACKST~1\AppData\Local\Temp\manifest.zip" --interactive false
(×) Error: m365.InternalError: Request failed with status code 429 (tracingId: ) undefined: undefined

STDERR:
(×) Error: m365.InternalError: Request failed with status code 429 (tracingId: ) undefined: undefined

Error: Unable to start debugging.
Error: Unable to sideload the Office Add-in.
Error: Command failed: npx -p @microsoft/m365agentstoolkit-cli atk install --file-path "C:\Users\JACKST~1\AppData\Local\Temp\manifest.zip" --interactive false       
(×) Error: m365.InternalError: Request failed with status code 429 (tracingId: ) undefined: undefined

Steps to Reproduce

Please provide detailed steps for reproducing the issue.

1. Create a unified manifest Office Addin project
2. Use office-addin-debugging to attempt to start the project locally
3. Observe the error

Context

First noticed on office-addin-debugging version 6.0.4 but have reproduced on latest version 6.0.6 too.

This entirely blocks debugging unified manifest apps. An equivalent XML manifest for the same project does not suffer this issue and can sideload and launch as expected.

Possibly related to: https://github.com/OfficeDev/microsoft-365-agents-toolkit/issues/14684#issuecomment-3502090793

Failure Logs

Please include any relevant log snippets, screenshots or code samples here.

Start by reproducing the failure with a unified manifest using the office-addin-debugging start manifest.json command on versions 6.0.4 and 6.0.6, and compare it with the working XML-manifest flow. Review the referenced Microsoft 365 Agents Toolkit issue and trace the reported 429 from the atk install invocation. Done means unified manifests can be sideloaded and debugging starts without the 429 error.