Russian diesel has moved from being the main bullish factor in global middle-distillate markets in 2025 to an overwhelmingly bearish force by early 2026, reversing a year-long surge in refining margins. The European diesel crack spread rose from $16.7/bbl in early January 2025 to $34.17/bbl in November as Russian supply – already structurally weakened since the start of the war – slid into acute shortage. That squeeze has now eased with the diesel crack spread averaging $21.7/bbl in January 2026. Refinery repairs, recovering runs and…