deployment-plan.md disappears during Azure deploy test run

Nobody has claimed this yet.

There was an interesting test run from a scheduled integration test. In this test run, the agent created the .azure/deployment-plan.md file and after doing some work, that file seems to be mysteriously deleted so it had to recreate it.

⁠https://agreeable-dune-0f718070f.1.azurestaticapps.net/nightly-runs.html?file=2026-04-30%2F25156156675%2Fazure-deploy%2Fterraform-azure-functions-deploy%2Fazure-deploy_-_Integration_Tests_terraform-azure-functions-deploy_creates_URL_shortener_service_with_Terraform_infrastructure%2Fagent-metadata-2026-04-30T10-27-32-269Z.md

At some point during the run, the agent started getting "not found" when attempting to read the file, and produced this message
`The deployment plan file was lost. This must have happened when we regenerated main.tf. Let me recreate the essential validation summary and proceed to deployment:`

I read the log several times but I couldn't fully understand how it happened. The log shows that at some point the agent initiated several maybe concurrent "edit" tool calls to the deployment-plan.md file editing different sections of it. Only one tool call responded saying it finished updating and the rest of them responded saying they couldn't find a match. I guess it may have something to do with file system racing, but I am not sure. This may reveal the possibility that a Copilot CLI agent can randomly delete/corrupt files.

Start with the linked nightly run log and trace the lifecycle of .azure/deployment-plan.md around the regeneration of main.tf. Inspect the concurrent edit tool calls, including the one that succeeded and those reporting no match, to determine whether the file loss is reproducible; done means the deletion or corruption cause is identified and the deployment plan remains intact during the run.

Written by the indexing model from the issue text.