[MarioPym]

Summary

printErrorPage() and printExceptionErrorPage() always call http_response_code(). When they are reached after output has already been sent (for example an error in the middle of a download, or an uncaught exception handled by the global exception handler), PHP logs "http_response_code(): Cannot set response code - headers already sent", which hides the real error in the log.

The status code cannot be changed at that point anyway, so this only sets it while headers can still be sent. The check lives in a small private helper used by both methods.

This is the same warning as #45835. #47971 fixed it for one caller in OC_Files; this guards the error page itself so it covers every path.

The test runs the code in a separate PHP process, because PHPUnit buffers the test output and headers are never sent inside the test itself.

How to test

1. Create a small script that sends output before showing an error page,
   e.g. ocs-provider/demo.php:

   <?php
   require_once __DIR__ . '/../lib/base.php';
   echo "output already sent\n";
   flush();
   \OCP\Server::get(\OCP\Template\ITemplateManager::class)->printErrorPage('Demo', 'late error', 500);

2. Open it in the browser or with curl https://your-instance/ocs-provider/demo.php.
3. Check data/nextcloud.log:
   • Before: http_response_code(): Cannot set response code - headers already sent ... TemplateManager.php#72
   • After: no warning.
4. The same happens with printExceptionErrorPage(new \RuntimeException('Demo'), 500).
5. Error pages without previous output still return their status code (e.g. 503).

Unit test: tests/lib/Template/TemplateManagerTest.php

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

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