impact --depth N misses dependents within N hops (depth-limited DFS marks nodes visited at the limit) #1974

codegraph impact <symbol> --depth N, and multi-depth callers, leave out dependents that are within N hops.

On main (ba3c21e):

export function t(){}
export function a(){ t(); }
export function b(){ a(); t(); }
export function c(){ b(); }

codegraph impact t --depth 2   → t, a, b        (expected t, a, b, c: c → b → t is 2 hops)
codegraph impact t --depth 3   → t, a, b, c

Cause: getImpactRecursive (src/graph/traversal.ts:543-600) and getCallersRecursive (:270-317) are depth-limited DFS walks with one shared visited set. Here b is first reached through a at depth 2, the limit, so it's marked visited without being expanded. When it's reached again directly from t at depth 1, it's skipped, so c is never found. Which dependents go missing depends on edge order.

The viewer's blast radius uses the same call (src/ui-server/api/node.ts:462, stats.ts:71, depth 3), so it undercounts the same way.

Suggested fix: walk level by level, as traverseBFS in the same file does, or re-expand a node when it's reached at a smaller depth than before. #1089 fixed a related gate in the same function (dropped edges), but not this. The open changes in #1583 / #1352 keep the recursive DFS, so they don't cover it either.