The project-patch (user_patches) gate loop is written five times, and scan's and vendor's copies have drifted #1911

[agent] Filed by the scheduled architecture audit (audit-cli-tests). Register: register comment.

Kind: refactor. Register ID: T38.

Problem

Five places each loop over purls doing the same steps: filter by selected ecosystem, call index.conflicts(purl), build detail, then sort the purl into allowed (a warning) or conflict (a refusal):

• user_patches.rs partition L70-L93
• evidence L98-L117
• skip_protected L138-L175
• scan/mod.rs L2244-L2273,``` an inline retain
• vendor.rs L2434-L2469, which renders partition's output by hand

The copies have drifted:

• scan's copy skips any_detectable and purl_ecosystem_selected, and its Skipped event has no uuid (skip_protected adds with_uuid).
• vendor calls dedup() without sort(), while check sorts first. It also prints one Error: per conflict, while user_patches::refuse prints the joined message.
• Warnings travel as (String, String) tuples, and callers turn them into RunWarning {code, detail} literals (vendor.rs L2440).

Eject also checks the gate three times: unlocked at vendor.rs L1821, locked at L2076, and inside VendoredBackend::apply at vendored_backend/mod.rs L99.

Proposed change

• Keep one user_patches::gate(common, purls) -> Gate { allowed: Vec<RunWarning>, conflicts: BTreeMap<purl, String> }.
• evidence, skip_protected, scan and vendor all consume it.
• refuse is the only human/JSON renderer for conflicts.
• Drop the (String, String) warning tuples.

Size

user_patches.rs, scan/mod.rs, vendor.rs, vendored_backend/mod.rs. About −70 / +30 lines.

Acceptance criteria

• user_patch_conflict and user_patch_override codes, envelopes and exit codes are unchanged.
• tests/user_patches.rs and the scan and vendor project-patch e2e tests stay green.
• scan's Skipped events gain the uuid, which is additive.