Plugin and Consumer ADR numberings share a namespace, and /build schedules the collision

The problem

Two facts, both measured on 2026-08-24 while resolving #407/#401 (PR #413):

1. A bare ADR-NNNN in a Box always means a plugin ADR — that convention is now one sentence in the plugin's AGENTS.md (§ "A Box is read where it runs"), chosen over qualifying the ~88 bare citations across the four Box YAMLs, because a citation carrying its own repository is a sentence nobody keeps current.
2. /build grows the Consumer's own docs/adr/ — unic-dlc-build.yaml's report node drafts docs/adr/NNNN-<slug>.md into the Consumer. DXP-DesignSystem already holds 0001 and 0002; the Boxes cite 0011 upward.

So the two numberings share a namespace, and the collision is scheduled, not hypothetical: enough /build runs and the Consumer mints an ADR-0011 of its own, at which point every bare citation in every installed Box resolves ambiguously — the harder-to-notice defect class (#401's plausible-but-wrong pointer, one level up).

The maintainer chose at #413's merge to keep the one-sentence convention for now. This ticket tracks the collision itself.

What a resolution decides (not decided here)

• Whether /build's report node numbers Consumer ADRs from a floor (e.g. above the plugin's highest citation), prefixes them, or the collision is handled at read time by the convention sentence alone.
• Whether the plugin's ~88 bare citations ever get qualified, and if so by what rule that does not rot (the objection that killed qualifying them in #413).
• Who owns the fix: the Box prose (plugin), the Consumer's ADR README, or both.

Acceptance criteria

• The collision-handling rule is decided and written where it acts: /build's report node prose, the plugin AGENTS.md bullet, or both — with each surface naming the other.
• The rule is stated for the collision case, not only the clean case: what a reader does when ADR-0011 exists in both trees.
• DXP-DesignSystem's current ADR count is re-measured at implementation time — this body's 0001/0002 is a 2026-08-24 snapshot and will be stale.

Context

• Found by wayfinder-407 while resolving #401's cross-reference sweep; the maintainer's choice to defer is recorded in PR #413's review-trail summary comment.
• Related: #401 (the pointer-ambiguity class), ADR-0027 (superseding works across both ADR homes — the one plugin surface that already knows two homes exist).

Start by reading the report node in unic-dlc-build.yaml, the plugin AGENTS.md bullet, and the PR #413 review-trail summary. Re-measure DXP-DesignSystem's current ADR count, then decide and document the collision rule on the relevant surfaces, including what readers do when the same ADR number exists in both trees.