Issue #3590969 by ezeedub: BigPipe accumulates duplicate library entries causing AssertionError

Edward Zwartrequested to merge
issue/drupal-3590969:3590969-bigpipe-accumulates-duplicate into main

In sendNoJsPlaceholders(), wrap array_merge() with array_values(array_unique()) when accumulating already-loaded libraries, preventing duplicate entries that trigger an AssertionError in LibraryDependencyResolver::getMinimalRepresentativeSubset().

Change catch (\Exception $e) to catch (\Throwable $e) in all placeholder- rendering catch blocks so \Error subclasses (including AssertionError) are caught and logged via trigger_error() rather than escaping uncaught.

Closes #3590969

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