Decide completeness by par2 set for releases without a counter

59% of settled releases had complete = NULL: without an [i/N] counter
the settler left it unknown, and the "phase 2 reads par2 sets for those"
step was never built. A release is now complete when every file its par2
sets describe is there by name or by its first-16-KiB hash, or, for an
upload renamed after its par2 was made, when it has as many non-par2
files and bytes. Decided when a par2 index is probed, after a par2 merge,
and before the pruner drops a set's file list; the batch store, settler
and merger keep a decided value instead of resetting it to NULL.
releases:par2-complete decides the releases probed before this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

REBUILD.md

@@ -189,10 +189,14 @@ dropping garbage; 28 TB of compressed overview traffic. Throughput goal:
    number; merged when the neighbouring range is done, then written as a
    chunk. Never staged per segment.
 
-8. **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.
+8. **Settling**. A release is settled when nothing was added to it for 6
+   hours (30 minutes once its last post is that old: history), and its
+   completeness decided: complete when every file its [i/N] counter
+   announced was found. Without a counter, by its par2 sets once their index
+   is probed (`par2_completeness`): every file a set describes is there by
+   name or by its first 16 KiB, or, renamed, as many files and bytes; decided
+   again after a par2 merge and before the pruner drops a set's file list.
+   Segments aren't compared. Phase 2 picks its work from settled releases.
 
 9. **NZB and API**. NZB built from a release's chunks; a minimal Newznab
    search (names) and get. Web UI later.