Add governed ALZ edition probe

docs/API_CONTRACTS.md

@@ -414,11 +414,15 @@ not marked stale merely because their source date is old. Unknown sources are
 
 ### GET `/api/v1/projects/{project_id}/datasets/source-catalog-probes`
 
-Performs an explicit, read-only release probe for the allowlisted GRB WFS and
-most-recent orthophoto WMS. The endpoint reads bounded `GetCapabilities`
-responses, confirms the expected layers and follows only HTTPS ISO 19139
-`GetRecordById` links on `metadata.vlaanderen.be`. Query parameter
-`refresh=true` bypasses the short in-memory response cache.
+Performs an explicit, read-only release probe for the allowlisted GRB WFS,
+most-recent orthophoto WMS and ALZ agricultural-use parcel publication page.
+For OGC services, the endpoint reads bounded `GetCapabilities` responses,
+confirms the expected layers and follows only HTTPS ISO 19139 `GetRecordById`
+links on `metadata.vlaanderen.be`. For ALZ, it reads only the bounded official
+HTML release page and accepts only exact
+`www.landbouwvlaanderen.be/bestanden/gis/agpa_<year>_<date>_public.zip` link
+identities. It does not request those archives. Query parameter `refresh=true`
+bypasses the short in-memory response cache.
 
 Each provider item returns service reachability, matched/missing layers, the
 official metadata identifier, title, edition, publication/metadata dates,
@@ -427,6 +431,13 @@ local `source_version` and one comparison status: `same`, `different`,
 `available`, `degraded`, `unavailable` or `disabled`. A difference means only
 that an operator should review provenance; it is not an update instruction.
 
+ALZ comparisons use only the latest definitive third snapshot, normalized as
+`<campaign>-v3`. A newer first or second snapshot is reported in the item title
+and message as provisional but cannot mark a local definitive historical
+edition as outdated. `service_type=HTML` uses `definitive_archive` and
+`current_snapshot` as evidence markers in the existing expected/matched/missing
+arrays; no parallel response shape is introduced.
+
 The endpoint accepts no arbitrary URL, feature query, area or layer. It does
 not fetch vector features, raster pixels or models, create jobs/datasets, write
 to PostGIS or trigger an import. The normal `source-freshness` endpoint remains