[P0] Audit: Legacy category URLs create duplicate taxonomy pages

[baixiangcpp]

Imported from the byteflow.tools deep audit on 2026-06-22.

Problem: legacy category URLs are still reachable and overlap with the current 8-category taxonomy.

Affected URLs:

• https://byteflow.tools/en/web-api
• https://byteflow.tools/en/design-media
• https://byteflow.tools/en/convert-encode
• https://byteflow.tools/en/web-api-network
• https://byteflow.tools/en/images-svg-css

Reproduction steps:

1. Open /en/web-api and observe that it renders as a standalone Web & API hub.
2. Open /en/web-api-network and compare category name, intent, tool count, and tool list.
3. Repeat with /en/design-media vs /en/images-svg-css.
4. Repeat with /en/convert-encode vs current format/encoding categories.
5. Inspect canonical tags and sitemap inclusion.

Expected behavior: only current category URLs should be indexable and internally promoted. Legacy taxonomy pages should 301/308 redirect to the closest current category, or use canonical tags and be removed from sitemap.

Actual behavior: legacy URLs render as independent pages and can compete with current category pages.

Impact: duplicate taxonomy pages, split internal link equity, inconsistent tool counts, crawler confusion, and weaker SEO quality signals.

Proposed fix:

• Redirect /en/web-api to /en/web-api-network.
• Redirect /en/design-media to /en/images-svg-css.
• Decide the best canonical target for /en/convert-encode.
• Remove legacy URLs from sitemap.
• Update all internal links.
• Add routing regression tests.

Acceptance criteria:

• Legacy URLs return 301 or 308 to selected canonical current category pages.
• Sitemap contains no legacy taxonomy URLs.
• Current category canonical tags are self-referential.
• No navigation, footer, workflow, cluster article, or tool card links to legacy category URLs.

[baixiangcpp]

Closed as completed by the canonical BF audit backlog work. This older non-BF audit issue duplicates work now merged through PRs #209-#219, with the BF issues closed and guard/test coverage in place. The remaining non-duplicate follow-up is #7, which stays open because the upstream Next/PostCSS advisory is not fixed yet.