Harden Cache-Control TTL sanitization in response controller

[MaximillianGroup]

Motivation

• Prevent third-party filters from producing negative or invalid Cache-Control directive values which can create malformed headers and unpredictable downstream caching behavior.

Description

• Normalize starcache_max_age and starcache_stale_while_revalidate outputs in StarResponseController::sendPublicCacheHeaders() by introducing sanitizeDirectiveSeconds() and using it to ensure non-negative, predictable TTLs (file modified: StarResponseController.php).

Testing

• Ran syntax checks php -l across plugin PHP files which completed successfully.
• Attempted composer install / composer test but dependency installation failed due to Packagist network restrictions in the execution environment, so full test-suite execution could not be run.

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Codex Task

[gemini-code-assist]

Code Review

This pull request introduces a new helper method sanitizeDirectiveSeconds to normalize cache directive durations (max-age and stale-while-revalidate) to prevent negative or invalid values from third-party filters. The feedback points out that casting the filter outputs to (int) before sanitization converts invalid types (like null or false) to 0, which bypasses the negative-value check and silently disables caching. The reviewer recommends passing the raw filter values and updating sanitizeDirectiveSeconds to accept mixed types and validate them using is_numeric() to safely fall back to the default TTL.

[Copilot]

Pull request overview

This PR hardens Cache-Control header emission by preventing negative TTL values (potentially returned by third-party WordPress filters) from producing malformed directives in StarResponseController::sendPublicCacheHeaders().

Changes:

• Added sanitizeDirectiveSeconds() to normalize directive seconds to a non-negative integer.
• Applied sanitization to both starcache_max_age and starcache_stale_while_revalidate filter outputs before building the Cache-Control header.

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