Bring Engineer documentation to the ecosystem task-quality standard #63

Problem

The 2026-09-24 ecosystem documentation review found that Engineer does not yet give readers a verified route from every principal workflow to a task guide, exact public API reference, runnable installed-wheel example, and relevant book notebook. The Book Guide uses an obsolete chapter layout: none of its 17 concrete companion paths resolves at the checked book revision, and three case-study paths are templates. The synthetic quickstart also lacks an observable expected result.

Required outcome

Readers can complete Engineer's principal feature, labeling, alternative-bar, dataset-building, preprocessing, fractional-differencing, and discovery tasks with the released API, verify the result, and open semantically relevant public book files directly. Book links use one checked companion commit and state whether each file calls Engineer, teaches the method manually, or illustrates a related workflow.

Scope

• Inventory principal capabilities against task guides, API reference, runnable examples, and book files.
• Preserve and improve the existing feature, labeling, alternative-bar, and dataset-builder guides.
• Add an observable expected result to the synthetic first workflow.
• Rebuild the Book Guide from the companion tree at d2edec54b1c7a6a9d7a97d8129eb05db4491e1eb.
• Run one complete built-wheel example for each core workflow.
• Document unsupported and experimental boundaries.
• Explain Alphalens overlap only for specific factor-preparation tasks that Engineer supports; leave broader factor analysis to Diagnostic.

Out of scope: changing the book, old Quantopian repositories, another library's documentation, or public runtime APIs.

Acceptance criteria

• The home page and navigation route readers to first use, task guides, exact API reference, and the Book Guide.
• Principal examples run from the built wheel in a clean environment and expose assertions or deterministic output.
• External-service or hardware examples state requirements and the narrow safe verification limit.
• Book links are direct, commit-pinned, path-checked, semantically classified, and reciprocal from the Book Guide to the relevant task guide.
• The PR records the capability inventory, example runs, companion revision and path checks, rendered/internal-link checks, strict MkDocs build, full repository gates, and remaining exceptions.
• The private sidecar records the issue and PR links, review evidence, and any work left for another owner.

Compatibility

Documentation and verification only. No public API or runtime behavior change is intended.