-g agent scan + rollback silently unpatch a hosted NuGet project's install #1793

[agent] Split out of #489 (the hosted-mode variant from #489 (comment), reported 2026-10-01).

Summary

A hosted NuGet project's locked restore extracts the Socket-feed nupkg into the global packages folder (~/.nuget/packages or NUGET_PACKAGES). A global agent run started in that project treats the copy as a separate global install. scan -g --mode agent --yes reports applied: 1 and writes an agent record. rollback -g --yes then restores upstream bytes into it with rolledBack: 1. The next dotnet restore --locked-mode says "up-to-date" and keeps the pristine bytes, so the project builds unpatched with exit 0 everywhere.

This predates #446: -g never consulted the project's hosted pins. #1790 fixes the vendored half of #489. It treats the project's vendored NuGet packages as ledger-owned when the global folder is one the project restores into (NuGetCrawler::global_roots_shared_with, commands::vendor_owned_keys).

Why it's separate

Hosted mode has no ownership skip even in project scope. Agent scan over a hosted pin warns (hosted_wiring_retained) and proceeds, and project-scope rollback unwinds the pin through its hosted leg. Under -g neither the hosted leg nor the warning runs. Fixing this needs a contract decision: either a new skip reason/code for "hosted pin owns this copy" in scan/apply/rollback under -g, or running discovery under -g and reusing hosted_wiring_retained plus a rollback skip. That's new CLI surface, not the vendored ownership rule #1790 restores.

Repro

As in #489's hosted comment: the e2e_nuget_dotnet_build hosted fixture, scan --mode hosted, a locked restore, then scan -g --mode agent --yes and rollback -g --yes with NUGET_PACKAGES set to the restore's folder.

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