Feature: mid-run checkpoint + adaptive downgrade to hybrid touches during `analyze`

[stephenc222]

Motivation

Follow-up from #163 (spike on predicting analyze --per-function-touches runtime ahead of time). Discussed there: a pre-flight runtime estimate is one way to avoid timeout crashes on large repos (see golang/go failing hotspots-cloud's 900s budget at 445MB — under its 500MB size-based cutoff for hybrid-touches routing).

This ticket tracks a different, complementary approach that doesn't depend on getting a predictive model right: make analyze self-correcting at runtime instead of requiring callers to predict cost upfront.

Proposal

While running --per-function-touches, track progress (functions processed / total, elapsed time) and expose a way to auto-downgrade to hybrid touches mid-run if the observed processing rate projects past a caller-supplied budget (e.g. --budget-seconds). This avoids:

• Requiring an accurate cost model (the spike in Spike: predict analyze runtime ahead of time to avoid timeout crashes on large repos #163 may or may not produce one that generalizes well)
• Wasted full re-runs after a timeout crash — currently a timeout just kills the process with zero output, discarding all completed work

Notes

• This is a concrete feature, not research — no spike needed before scoping it, though it pairs well with whatever comes out of Spike: predict analyze runtime ahead of time to avoid timeout crashes on large repos #163 (a rough pre-flight estimate could set a smarter default budget, but isn't required for this to work).
• Callers like hotspots-cloud currently guess the touch mode upfront from size_kb and hope the fixed external wall-clock timeout doesn't fire; a --budget-seconds + adaptive downgrade would let hotspots itself gracefully degrade instead of being killed from outside.

Related

• Spike: predict analyze runtime ahead of time to avoid timeout crashes on large repos #163 (predictive runtime spike)
• hotspots-cloud crawl failure this stems from: https://github.com/Stephen-Collins-tech/hotspots-cloud/actions/runs/33952911364