[sgf36]

Summary

• New packaging/submit_to_store.py script that automates Microsoft Store MSIX submissions via the Partner Center submission API (manage.devcenter.microsoft.com), mirroring the MAS auto-submit flow on macOS.
• CI step added to the Windows leg of build.yml, gated on PARTNER_CENTER_CLIENT_SECRET — no-op until secrets are configured.
• CI-STORE-SUBMISSION-SETUP.md documents the one-time Azure AD app association and repo secret setup.

How it works

1. Authenticates with Azure AD client credentials (tenant ID, client ID, client secret)
2. Creates a new submission (clone of last published)
3. Marks old packages for deletion, adds the new signed MSIX
4. Updates releaseNotes across all listing locales from store_assets/RELEASE-NOTES-{version}.md
5. Uploads the MSIX (in a ZIP) to the SAS blob URL
6. Commits the submission and polls until accepted for certification

Secrets needed (once this PR merges)

Secret	Value
PARTNER_CENTER_TENANT_ID	Azure AD tenant ID
PARTNER_CENTER_CLIENT_ID	Azure AD app client ID
PARTNER_CENTER_CLIENT_SECRET	Client secret from Partner Center
PARTNER_CENTER_APP_ID	Internal Partner Center application ID

Test plan

• CI passes on this PR (the Store submission step is gated — it will be skipped since secrets don't exist)
• After merge: add the four secrets, push a commit to main, verify the "Submit MSIX to Microsoft Store" step runs in the Windows leg
• Confirm the submission appears in Partner Center with the correct MSIX and release notes

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