PackageInstaller writes node-repo installs one node at a time — bulk-save would cut course installs by minutes #815

Measured on Systemorph/education's blocking e2e gate (the ~27-35 min install job): the dominant cost is not image pulls (0.9-1.5 min incl. both ACR pulls) but per-course install time, because PackageInstaller.cs writes node-repo installs one node at a time (Concat, ~line 455) with a 100 ms visibility-barrier poll per node. A course of ~300 nodes pays that serial round-trip tax on every install — on the disposable mesh AND on every production install.

Proposed: batch the node writes (bulk save per install, one visibility barrier at the end), keeping the per-node validation. The education e2e's install-verification flow (coupon → import → mesh nodes → bulk save → race-free) is the acceptance shape.

Evidence and timing breakdown in Systemorph/education#98's analysis (comment on the e2e-install job + AGENTS.md note explains why caching was measured and rejected).

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