The last standalone Help popup — lib/general/show_help.php — is modernized as a standalone Dashio screen backed by a REST BFF. The legacy controller was broken dead code on the upgraded branch (it referenced the undefined constant TL_HELP_RPATH and rendered gui/help/<locale>/*.html files that had been deleted — their content was migrated into the locale $TLS_htmltext / $TLS_htmltext_title arrays in locale/<loc>/texts.php). Modernizing the screen restored the functionality.

The TODO section of docs/MODERNIZATION-STATUS.md is empty: every ASIDE entry was already verified to map to a modern gui/templates/**/*.html screen

• BFF. Per the modernize.yml guidance ("if the TODO section is empty, say so in one line, then pick the smallest coherent one"), the Help popup was chosen — the last standalone lib/general/* screen with no dedicated modern screen. api/staticpage (#1501) serves the same $TLS_htmltext source for the 16 context-help keys from the Work Area; the modern Help popup exposes them all from a standalone popup plus keeps the legacy show_help.php redirect shim.

• Screen: gui/templates/help/showHelp.html — Dashio popup with teal header, 16-topic sidebar (populated from the BFF index on every load, so a direct-key open still fills the list), content card rendering the legacy help HTML body, active-topic highlight, TLi18n locale switcher (survives ?help= on reload), Refresh/Close tool buttons, a notFound warn bar for unknown keys ("Help topic not available in the selected language") with the legacy "ask administrator to update localization file" body (HTTP 200, legacy parity), and a localized footer.
• BFF: api/help/index.php — session auth + bffSameOriginGuard:
  • GET ?action=index — 16 help topic items {key, title, hasContent} from the locale $TLS_htmltext/$TLS_htmltext_title texts.php bundles.
  • GET ?action=show&help=<key>[&locale=xx] — {key, title, content_html, notFound, locale}; unknown keys return the localized legacy missing-key message with notFound:true.
  • JSON contract 401 (anon) / 400 (invalid key or action params) / 405 (unknown action) / 500 (no bundle at all).
  • Security (code-review #1552): the session/default locale is validated ^[a-z]{2}_[A-Z]{2}$ + is_file(locale/<loc>/texts.php) before include — closes the legacy @TODO directory-traversal hole; BOM-emitting texts.php bundles (fr_FR, es_AR) are included under ob_start()/ob_end_clean() so the JSON response stays valid; the 2-letter ?locale= hint is whitelist-mapped (en→en_GB, ro→ro_RO, …) and honoured only against a shipped texts.php. A locale without a texts.php (e.g. ro_RO) silently falls back to en_GB and reports the real bundle locale.
• i18n: hlp.* (7 keys: title/headerSub/topics/chooseTopic/loadError/ notFound/noTopics) + footers.showHelp + common.close in all 10 bundles (en/ro/de/es/fr/it/ja/pt/ru/zh; en_GB's sibling conventions kept).
• Link switch: open_help_window() in gui/javascript/testlink_library.js now opens gui/templates/help/showHelp.html?help=<page>&locale=<locale> (both values encodeURIComponented, popup widened 400px→780px).
• Shim: lib/general/show_help.php kept as a session-guarded 302 onto the modern screen (URL built on $_SESSION['basehref'], preserving the legacy link contract).

• Browser (admin session): direct key open (?help=editTc) with sidebar populated + active highlight; topic click swap; locale switcher EN↔FR (French bundle starts with a UTF-8 BOM — response stays valid JSON); unknown key → warn bar + legacy body; legacy show_help.php 302→ modern screen. Console clean (0 error/warn).
• BFF curl contract: 401 anon, 405 unknown action, 400 invalid/traversal key, 200+notFound:true unknown key, 16-item index, locale fallback reporting.
• Event Viewer clean after the run (only the 2 GUI-LOGIN AUDIT rows).

Suite 1552 (Screen — Help popup) in tmp/TLU_Test_Cases.md.

Screenshots: docs/screenshots/help-showHelp.png, docs/screenshots/help-showHelp-fr.png.