diff --git a/README.md b/README.md
index 6b31bdd..2a5f5de 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,7 @@ reviews / messages / memberships / requests / listing-meta
 ---
 
 Registered keys HivePress keeps in core columns instead of meta (`hp_vendor`, `hp_status`, …): see [docs/REGISTERED-KEYS.md](docs/REGISTERED-KEYS.md).
+What the HivePress extensions write and how they query it (dev36 inventory, D04 decision): see [docs/HIVEPRESS-COVERAGE.md](docs/HIVEPRESS-COVERAGE.md).
 
 ## Requirements
 
diff --git a/docs/HIVEPRESS-COVERAGE.md b/docs/HIVEPRESS-COVERAGE.md
new file mode 100644
index 0000000..bf7d8ee
--- /dev/null
+++ b/docs/HIVEPRESS-COVERAGE.md
@@ -0,0 +1,61 @@
+# HivePress coverage: what the extensions write and how HivePress queries it
+
+Read-only inventory on **dev36** (2026-09-27): HivePress 1.7 with blocks, bookings,
+favorites, marketplace, memberships, messages, requests, reviews, seo, social-links and
+tags; 101,175 listings, 1,499 vendors, 709 requests. The data is seeded, so features the
+seed never used show no rows — noted per line. Account pages (favorites, messages,
+memberships) were not crawled (login).
+
+## Meta keys written (rows, `hp_*`)
+
+| Post type | Key | Rows | Registered group | Queried? |
+|---|---|---|---|---|
+| hp_listing | `hp_hourly_rate` | 101,157 | `hp_listing_core` | yes — filter BETWEEN, sort |
+| hp_listing | `hp_price` | 100,437 | `hp_listing_core` | yes — filter BETWEEN, sort |
+| hp_listing | `hp_rating`, `hp_rating_count` | 53,299 | `hp_listing_core` | `hp_rating` sort |
+| hp_listing | `hp_verified` | 31,985 | `hp_listing_core` | no |
+| hp_listing | `hp_featured` | 5,131 | `hp_listing_core` | yes — featured block (`= CHAR`, `meta_key` + `rand`) |
+| hp_listing | `hp_warranty` | 100,401 | — | no (seed data: values are not warranty term ids; see below) |
+| hp_vendor | `hp_rating`, `hp_hourly_rate`, `hp_rating_count`, `hp_verified` | 761–1,499 | `hp_vendor_core` | `hp_hourly_rate` filter, `hp_rating` sort |
+| hp_vendor | `hp_availability` | 4 | — | no |
+| hp_request | `hp_budget` | 709 | `hp_request_core` | yes — filter BETWEEN, `meta_value_num` sort |
+| hp_request | `hp_due_date` | 709 | — | no |
+| hp_booking | `hp_start_time`, `hp_end_time` | 1 | `hp_booking_core` | no (1 booking) |
+| `*_attribute` | `hp_edit_field_*`, `hp_filterable`, … | 3 each | — | attribute settings, read by ID |
+
+User meta and comment meta: no `hp_*` rows. Term meta: `hp_sort_order` 170, `hp_icon`
+153 (`hp_taxonomy`).
+
+## Where the extensions keep their data
+
+- **Reviews** — `hp_review` comments (5,324); rating in `comment_karma` (see
+  [REGISTERED-KEYS.md](REGISTERED-KEYS.md)).
+- **Requests / offers** — `hp_request` posts; offers are `hp_offer` comments (48), no meta.
+- **Messages** — `hp_message` comments (0 on dev36).
+- **Favorites** — 4 user meta rows (no `hp_` prefix); nothing to flatten.
+- **Bookings** — `hp_booking` posts (1); **memberships** — no plans on dev36.
+- **Tags / categories / select attributes** — taxonomies (`hp_listing_tags` 2,160,
+  `hp_listing_category` 101,175, `hp_listing_warranty` 720 relationships). A select
+  filter (`warranty=28`) becomes `tax_query hp_listing_warranty IN`, never a meta query.
+- **SEO, social links** — no rows on dev36.
+
+## Query shapes seen (front-end crawl, 18 URLs)
+
+- Search filters on number attributes: `hp_price` / `hp_hourly_rate` / `hp_budget`
+  `BETWEEN DECIMAL` — routed.
+- Sort: the named shape `(NOT EXISTS OR EXISTS)` on `hp_price`, `hp_hourly_rate`,
+  `hp_rating` with `orderby=<name>__order` — routed, flat-first since core 1.2.0;
+  requests sort by `meta_key=hp_budget` + `meta_value_num` (a secondary query here) —
+  a shape the router handles.
+- Featured block: `meta_key=hp_featured` + `orderby=rand`, and `hp_featured = CHAR`.
+- Every front-end search carries WooCommerce's `product_visibility NOT IN` tax query.
+- `HivePress\Components\Attribute::set_search_query` runs its own `get_posts()` inside
+  `pre_get_posts` (suppress_filters): not routable (~100 ms on dev36).
+
+## D04 (auto-register HivePress attributes): not now
+
+Every meta key HivePress queries on dev36 is already registered; select attributes are
+taxonomies; the unregistered keys that are written (`hp_due_date`, `hp_availability`,
+`hp_warranty`) are never queried. Auto-registration would only pay off on a site whose
+admin adds **filterable or sortable number / date attributes** — revisit then (a doctor
+check listing such attributes without a registered key would flag it).