diff --git a/REBUILD.md b/REBUILD.md
index 15d2eb3..46a933a 100644
--- a/REBUILD.md
+++ b/REBUILD.md
@@ -29,7 +29,16 @@ dropping garbage; 28 TB of compressed overview traffic. Throughput goal:
    into releases (`lib/release` rules) → drop garbage (random name +
    dropped signature or tool) → set aside per-article random subjects and
    obfuscated subjects (counted only; phase 2). Returns per batch: release
-   chunks, edge fragments, counters. Holds no state beyond its lease.
+   chunks, edge fragments, probe candidates, counters. Holds no state beyond
+   its lease.
+
+   **Probe candidates**: per release, the articles phase 2 should read, as
+   (release key, kind, message-id, file in its chunk): the first article of
+   the first archive volume (`.part01.rar`, `.rar`, `.7z.001`), of the par2
+   index (smallest `.par2`), and of a lone random-named file; for a 7z set
+   also its last volume (the listing is in the tail). At most a few per
+   release (~115 M releases → ~150–250 M articles), not one per file. Per-
+   article and obfuscated subjects get none (they need every article's body).
 
 3. **Chunk store** (bulk, append-only). One record per release per batch:
    its files' names, sizes and segment lists, compactly encoded (template
@@ -42,16 +51,21 @@ dropping garbage; 28 TB of compressed overview traffic. Throughput goal:
    aggregates once per batch (one upsert per release per batch), plus a
    small name index for search. ~115 M rows, ~50–100 GB.
 
-5. **Fragments**. Files crossing a range edge: kept by range and article
+5. **Probe queue**. The candidates, in the catalog's database: one small row
+   each (release, kind, message-id, chunk reference), priority by the
+   release's state (settled first) and kind (random names before readable
+   ones). Phase 2 takes them from here; phase 1 only fills it.
+
+6. **Fragments**. Files crossing a range edge: kept by range and article
    number; merged when the neighbouring range is done, then written as a
    chunk. Never staged per segment.
 
-6. **Settling**. A release is settled when the ranges covering its posting
+7. **Settling**. A release is settled when the ranges covering its posting
    span are done and no chunk arrived for a day: completeness is computed
    then (expected vs found files and segments). Phase 2 picks its work from
    settled releases.
 
-7. **NZB and API**. NZB built from a release's chunks; a minimal Newznab
+8. **NZB and API**. NZB built from a release's chunks; a minimal Newznab
    search (names) and get. Web UI later.
 
 ## Not in phase 1