Building HTML documentation instructions fails on clean clone

When cloning a fresh version of mathlib (https://github.com/leanprover-community/mathlib4/commit/9610549d4c892f252d1bb1a96bdde7bbedb7589b specifially) and running the instructions for building the HTML documentation fails with:

❯ lake -R -Kdoc=on update doc-gen4
  lake build Mathlib:docs
info: batteries: cloning https://github.com/leanprover-community/batteries to '././.lake/packages/batteries'
info: Qq: cloning https://github.com/leanprover-community/quote4 to '././.lake/packages/Qq'
info: aesop: cloning https://github.com/leanprover-community/aesop to '././.lake/packages/aesop'
info: proofwidgets: cloning https://github.com/leanprover-community/ProofWidgets4 to '././.lake/packages/proofwidgets'
info: importGraph: cloning https://github.com/leanprover-community/import-graph to '././.lake/packages/importGraph'
info: Cli: cloning https://github.com/leanprover/lean4-cli to '././.lake/packages/Cli'
info: mathlib: running post-update hooks
error: unknown library facet `docs`

System information:

❯ elan --version
elan 3.1.1 (71ddc6633 2024-02-22)

❯ lean --version
Lean (version 4.10.0, arm64-apple-darwin23.5.0, commit c375e19f6b65, Release)

❯ lake --version
Lake version 5.0.0-c375e19 (Lean version 4.10.0)

Start by reproducing the documented HTML build command on the referenced clean commit: lake -R -Kdoc=on update doc-gen4. Inspect how the documentation build exposes the docs library facet and verify the command succeeds after dependencies are fetched; done means the clean-clone documentation build completes without the unknown-facet error.