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Alternative approach: skip log.Fatal, write marker file directly

The current implementation routes Pebble's os.Exit(1) calls through log.Fatal, which gives us log lines, Sentry reports, and marker files — but runs the full logging pipeline on potentially corrupted in-process memory (these exits guard invariant violations in Pebble's cache, memtable, etc.).

A lighter approach that minimizes the window of running with corrupted state:

cfg.opts.ExitFunc = func(code int) {
    msg := fmt.Sprintf("pebble: invariant violation (exit code %d)", code)
    // Write marker file directly — no mutex, no logging infrastructure
    for _, spec := range stores {
        auxDir := filepath.Join(spec.Path, "auxiliary")
        _ = os.WriteFile(filepath.Join(auxDir, "_FATAL_EXIT.txt"), []byte(msg), 0644)
    }
    // Exit immediately — don't go through log.Fatal
    os.Exit(code)
}

Tradeoffs:

The direct approach is safer for invariant violations where in-process memory may be corrupted (e.g. cache linked list pointers, reference count underflow). The log.Fatal approach gives better observability but relies on the logging infrastructure's mutexes being independent from the corrupted Pebble state — which is likely but not guaranteed.