Completely black, opaque film usually points to the film being exposed to light before or during processing, not simple overdevelopment. If even the edge markings or DX barcodes are missing, that strongly suggests full fogging from light exposure.

A two-hour stand in caffenol is unlikely by itself to make the whole roll totally opaque, especially since caffenol is generally a compensating developer. So overdevelopment is not the most likely cause.

Other possibilities are that the caffenol mix or process was not correct, but using brewed coffee is also a likely issue: caffenol recipes are normally based on instant coffee because its concentration is known and repeatable. Brewed coffee can vary too much to be reliable.

Best next steps:

• Use a proven caffenol recipe from a trusted source.
• Use instant coffee, not brewed coffee.
• Verify your tank/loading process is fully light-tight.
• Check that agitation, times, and temperatures match the recipe.

So: full blackness usually means light leak/fogging first; inconsistent chemistry from brewed coffee is another possible contributing problem.