Identify and implement top five code reduction

Identify top 5 opportunities to massively reduce the amount of code (lines of code) in any part of the repo: - Similar functionality that can be unified and reused - Code that has been valuable but no more - A front end component or a group of them duplicate another component/page functionality. Use the most modern and nice looking - etc. Now implement them :)

Five single-home reductions shipped (api test walks and censuses onto census_ast, one oracle-head validator, dead test helpers, git ls-files onto tracked_files): -229 net lines, quick gate green, 4.9k changed-area tests green, PR #7791 queued in the merge lane. Live CP facts show every legacy shim still exercised, so a "massive" cut needs a product retirement decision (table in report). No UI surface affected. Memory: used mem-35351/35380/32769/12787/32667/5787; proposed 1 qa.