server: tests: fetch random media marker via /apply-template (#21962)

[ServeurpersoCom]

Overview

Fix CI

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES, python write, install and run the test on disposable pod

[ServeurpersoCom]

cc @ngxson if you prefer a separate helper let me know

[ngxson]

Actually I think allowing user to set the marker would be a more flexible approach.

Maybe we can add a logic in get_media_marker() to return the env var LLAMA_MEDIA_MARKER if it's set?

[ggerganov]

Make get_media_marker() thread-safe like this:

const char * get_media_marker() {
    static const std::string media_marker = []() {
        // allow user to pin a reproducible marker via env var (useful for tests and external pipelines)
        const char * env = getenv("LLAMA_MEDIA_MARKER");
        if (env && env[0] != '\0') {
            return std::string(env);
        } else {
            return std::string("<__media_") + random_string() + "__>";
        }
    }();
    
    return media_marker.c_str();
}