[Brett Samblanet (brettsam)]

Fixes #11873

Certain flows (namely worker specialization failures) could result in a SyncTriggers call being made against a placeholder host. This would result in a Warmup function being sent to the platform and could cause issues with scaling and metadata.

This change checks whether the current host is a placeholder and if so, skip the sync. Previous behavior checked if the environment was a placeholder but did not validate the active host.

Pull request checklist

IMPORTANT: Currently, changes must be backported to the in-proc branch to be included in Core Tools and non-Flex deployments.

• Backporting to the in-proc branch is not required
  • Otherwise: Link to backporting PR
• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• My changes do not require diagnostic events changes
  • Otherwise: I have added/updated all related diagnostic events and their documentation (Documentation issue linked to PR)
• I have added all required tests (Unit tests, E2E tests)

[Copilot]

Pull request overview

This PR prevents SyncTriggers from publishing placeholder-host trigger metadata (notably the WarmUp function) during the specialization window where placeholder mode has been cleared but the active host is still running the standby configuration, addressing the race described in #11873.

Changes:

• Add a guard in FunctionsSyncManager.TrySyncTriggersAsync to skip syncing when the active host is still in standby configuration.
• Add an integration test validating that a placeholder-only WarmUp payload is not published.
• Add an E2E test reproducing the specialization window and asserting WarmUp is not published.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs	Adds standby-host detection to prevent publishing placeholder triggers during specialization windows.
test/WebJobs.Script.Tests.Integration/Management/FunctionsSyncManagerTests.cs	Adds an integration test ensuring placeholder WarmUp trigger payload is not published.
test/WebJobs.Script.Tests.Integration/WebHostEndToEnd/SpecializationE2ETests.cs	Adds an E2E repro for the specialization race window and validates WarmUp isn’t published.

[Fabio Cavalcante (fabiocav)]

Approving, but left a comment and I think a follow up is required.