[AdaWorldAPI]

This picks up the open point from W8 (#1770): under a cyclic working set one focus larger than the budget, LRU rebuilds on every load. It adds MRU as a second victim order and measures both in drf-focus-probe.

Change

• Evict::{Lru, Mru} and FocusManager::evict_to_budget_by(budget, order).
• evict_to_budget is still LRU, so default behaviour is unchanged.
• Pinning and the stop rule are shared by both orders.

Measured (3 foci, one eviction pass after every load; each expected count was worked out by hand before the run and all matched)

workload	budget	LRU builds	MRU builds
cyclic ABC ×10 (30 loads)	3	3	3
cyclic ABC ×10	2	30	12
cyclic ABC ×10	1	30	21
phased AAAA BBBB CCCC ×2 (24 loads)	2	6	10

Neither order wins both workloads.

• Cyclic: MRU keeps two of the three foci resident.
• Phased: MRU evicts the focus it just loaded, so every load in the third phase rebuilds.

Checks

• 30 tests pass with --features handoff, on native and on x86-64-v3.
• clippy -D warnings is clean.
• Disable run: making Evict::Mru sort like LRU turns both new churn_* tests red.

Open. We have not measured what access pattern thought workloads actually have, so this PR does not change the default. The next candidates are a scan-resistant policy, which adapts between the two orders, and a fallback to direct reads; this PR tries neither.

Board: .claude/board/entries/2026-10-25-drf-churn-policy.md.

---

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-25T08:49:00.696018Z	45fbf43	Manual request

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Codex Review: Didn't find any major issues. 🎉

Reviewed commit: 45fbf437f2

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