Docs remediation: # Errors sections and runnable doctests

[shinaoka]

Scope correction (2026-08-10)

strided-einsum2 and strided-opteinsum are not being retired. Per #226, all nine workspace crates remain maintained. Any retirement/Phase 2 removal premise below is obsolete; re-audit and implement the acceptance criteria across the maintained workspace.

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Part of #199 (Phase 3, docs). All file:line references are pinned to origin/main at 9da9b9f. Mechanical follow-through once the rules issue lands.

Measured today: 172 public Result-returning functions, 9 with a # Errors section (strided-view 0 of 26). Re-measure and cover all nine maintained crates. Runnable rustdoc doctests in all of src/: 5. ignore fences: 9. strided-view has 114 public functions and zero compiled examples.

• Add # Errors sections naming concrete failure conditions across all nine maintained crates.
• Replace ignore fences with runnable doctests; add examples to the main entry points (map_into, zip_map*, reduce, reduce_axis, copy_into, plans, erased entry points, ExecutionPolicy).
• Consider porting tenferro's check-public-error-docs script as a CI gate once coverage is realistic.

[shinaoka]

2026-08-10 棚卸し

active, metrics need refresh。# Errors と runnable doctest の不足は残るが、元 count は retirement 前提で古い。#216 と #220 を先に landing し、全9 crate の public Result API/ignored fences を再計測する。主要 entry points から runnable examples を追加し、coverage が十分になった段階で checker を CI gate 化する。

Umbrella: #230。実装 PR の base は umbrella/issue-burndown-2026-08。