[research][overlay] Prioritize deferred interaction policies from concrete consumers

Select the next justified Overlay policy slice after ordinary cataloging, rather than treating every deferred field as an implementation backlog.

Existing boundaries

See M-OVERLAY-0001-D, C-AS-OVERLAY-0001, the three HC-OVERLAY-* entities and internal/records/2026-09-09-overlay-and-remaining-catalog.zh-CN.md. Generic focus entry/restore and anchor/trigger dismissal remain stored configuration; focus-outside is deferred. Web modal currently owns scroll lock, not complete inertness/focus-trap/A11y policy. Numeric layer arithmetic does not establish an absolute hierarchy. Accepted scoped Escape arbitration must remain intact.

Acceptance for prioritization

• Gather concrete Dialog/Dropdown/Tooltip or other consumer failures/needs with expected transitions.
• Separate focus entry/restore, anchor/trigger dismissal, focus-outside, stronger layer ordering and modal policy into independent ownership questions.
• Trace responsibility against Focus, Boundary, Trigger, Hit Participation, Presence/ViewIntent and A11y before choosing any transfer to Overlay.
• Select at most one demand-backed implementation candidate with lifecycle, controlled-state, nesting and cross-Adapter evidence boundaries, or explicitly defer all candidates for lack of demand.
• Obtain a maintainer decision for new semantics before implementation; preserve existing consumer-specific behavior until migration is governed.

No blanket implementation of all deferred policies, new absolute layer guarantee, automatic A11y certification or catalog lifecycle promotion. Cross-check existing #587 (mobile positioning synchronization) and #496 (Select positioning policy); this issue does not replace those narrower tasks.

Record

Direction: internal/records/2026-09-10-first-m-hc-a-catalog-closeout.zh-CN.md (closeout PR #641: https://github.com/Proto-UI/Proto-UI/pull/641). Records are non-normative; applicable spec and later accepted decisions govern implementation.

Start with M-OVERLAY-0001-D, C-AS-OVERLAY-0001, the three HC-OVERLAY-* entities, and the records dated 2026-09-09 and 2026-09-10. Trace concrete Dialog, Dropdown, Tooltip, Focus, Boundary, Trigger, Hit Participation, Presence/ViewIntent, and A11y needs, while cross-checking issues #587 and #496. Done means selecting one demand-backed candidate or deferring all candidates, with a maintainer decision and preserved consumer-specific behavior.