Build a directed graph where edge i→j exists if bomb j lies within bomb i's blast radius — use squared distance to avoid floating-point: `dx² + dy² ≤ r_i²`.

For each bomb as the starting point, run DFS/BFS to count how many bombs it can detonate through the chain. Track visited per-start to prevent infinite cycles.

The graph is directed: bomb A may reach bomb B but not vice versa. Test every bomb as the seed; return the maximum reachable count.