Honestly curious, have you seen agents succeed at this sort of long-trajectory wide breadth task, or is it theoretical? Because I haven't seen them come close (and not for lack of trying)

Yeah I absolutely see it every day. I think it’s useful to separate the research/planning phase from the building/validadation/review phase.

Ticket trackers are perfect for this. Just start with asking AI to take this unclear, ambiguous ticket and come up with a real plan for how to accomplish it. Review the plan, update your ticket system with the plan, have coworkers review it if you want.

Then when ready, kick off a session for that first phase, first PR, or the whole thing if you want.

In my expedience, Claude Code with opus 4.5 is the first one to tackle such issues well.

Opus 4.6, with all of the random tweaks I've picked up off of here, and twitter, is in the middle of rewriting my golang cli program for programmers into a swiftui Mac app that people can use, and it's totally managing to do it. Claude swarm mode with beads is OP.