Reveal teacher content via eXeLearning's ?exe-teacher URL param, retire CSS injection

[erseco]

⛔ Do not merge until exelearning/exelearning#1972 is merged. This PR depends on the core ?exe-teacher=1 contract introduced there; merging earlier would break teacher-mode reveal in the embed.

Why this simplifies the plugin (and where it's heading). Teacher-mode visibility is now driven purely by the package's own ?exe-teacher=1 URL parameter, so the host plugin no longer injects CSS/JS into the embedded package to control it. Beyond removing that injection, this advances the longer-term goal of isolating embedded resource content from the host: because the host no longer reaches into the package DOM, the resource can later be sandboxed / served cross-origin without losing teacher-mode control.

What

eXeLearning core now hides teacher-only content by default and exposes an in-package "teacher layer" selector to show it via the ?exe-teacher=1 URL parameter (upstream exelearning/exelearning#1972, fixes exelearning/exelearning#1772). This consumes that contract and retires the plugin's parent-side teacher-mode CSS injection.

Changes

• Removed classes/local/ui/teacher_mode_hider.php and the exelearning_require_teacher_mode_hider() lib.php helper that injected #teacher-mode-toggler-wrapper { visibility: hidden } into the package iframe.
• view.php now appends ?exe-teacher=1 to the content iframe src whenever the per-activity teachermodevisible setting is on — for every viewer.
• The teachermodevisible setting uses the "Show teacher layer selector" label/help, homogeneous across en/ca/es/eu/gl with mod_exeweb and mod_exescorm. Refreshed the matching install.xml / db/upgrade.php / mod_form.php comments.

Notes

• The setting alone controls the selector — no capability gate. When on, the in-package selector is available to every viewer; it is OFF by default in the package and the viewer activates it. Presentation mode, not access control.
• Targets main. No schema change and no version bump — the teachermodevisible field and its default-0 migration already shipped; this only changes how the setting is consumed.

Testing

• php -l clean; phpcs --standard=moodle clean on the changed files. Behat updated: the iframe src carries exe-teacher=1 when the setting is on (including for a student) and omits it when off; dropped the obsolete hider unit test. PHPUnit/Behat need a Moodle CI site.

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Moodle Playground Preview

The changes in this pull request can be previewed and tested using a Moodle Playground instance.

ℹ️ The eXeLearning editor is fetched from the shared release and unpacked into the plugin when the playground boots, so the first load may take a few extra seconds. ELPX upload, viewer and preview work normally.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.48%. Comparing base (4665b64) to head (16e3f9f).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##               main      #86      +/-   ##
============================================
- Coverage     89.51%   89.48%   -0.04%     
+ Complexity      980      979       -1     
============================================
  Files            53       52       -1     
  Lines          4236     4221      -15     
============================================
- Hits           3792     3777      -15     
  Misses          444      444              

Flag	Coverage Δ
javascript	94.03% <ø> (ø)
php	89.31% <ø> (-0.04%)	⬇️

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Components	Coverage Δ
PHP (server-side)	89.31% <ø> (-0.04%)	⬇️
JavaScript (SCORM tracker)	94.03% <ø> (ø)

Files with missing lines	Coverage Δ
lib.php	79.93% <ø> (-0.07%)	⬇️

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