[6.x] Fix search:update ignoring the index argument when index names are customized

[edalzell]

The problem

Customizing index names lets you rename an index at runtime, e.g. prefixing it per-environment:

Index::resolveNameUsing(fn ($name, $locale) => 'local_'.$name.'_'.$locale);

With a test index configured that way, php please search:update test doesn't update the index. It silently drops the argument and shows the "Which search index would you like to update?" prompt instead — and if you're not paying attention, accepting the default reindexes everything. On a single-index site it's worse: getIndexes() returns all indexes without prompting at all.

The cause

getRequestedIndex() resolved a configured handle by prefix-matching it against the resolved name:

if (collect(config('statamic.search.indexes'))->put('cp', [])->has($arg)) {
    return $this->indexes()->filter(fn ($index) => Str::startsWith($index->name(), $arg))->all();
}

That assumes the resolved name still starts with the handle, which holds for the default {handle}_{locale} naming but not once a resolver renames the index — local_test_en doesn't start with test. The filter comes up empty and returns [], which is falsy, so it slips past the if ($requestedIndex = $this->getRequestedIndex()) guard in getIndexes() and falls through to the prompt rather than erroring.

This is the same assumption that was already fixed for the insert job — Index::insertMultiple() passes $this->handle to InsertMultipleJob precisely because the resolved name can't be reversed back into the handle. Update is the remaining caller doing it by string manipulation.

The fix

Match on the configured handle, which Index already tracks in $this->handle. This adds a public handle() accessor to Index and uses it:

if ($indexes = $this->indexes()->filter(fn ($index) => $index->handle() === $arg)->all()) {
    return $indexes;
}

This was written by good ol' Claude. I've reviewed the change and the tests, and confirmed the new test fails on 6.x and passes with the fix.