Reading breadth-first — understanding the system boundary before the internals — applies AT6 (Flexibility vs Simplicity). Breadth-first reading is slower to get to any specific file but faster to understand the whole. Depth-first reading gets to specific files fast but can produce a detailed understanding of the wrong layer.
For urgent situations, F6 and F3 are sufficient to generate the first hypothesis. Identify the archetype, enumerate the most likely failure modes given what is visibly broken, check the most exposed component. This is not a complete system read — it is a diagnostic probe. AT6 applies in the other direction: accepting less completeness for faster action.
The tradeoff in both cases is AT9 (Correctness vs Performance). A more complete system read produces better hypotheses, but better hypotheses are only valuable if there is still time to act on them.