Release 0.9.0

Product version to 0.9.0, frontend in lock-step, Unreleased notes moved into a
dated section per ADR-007. The plugin contract stays at 0.16.0: it moved after
v0.8.1 and is already recorded in this release's notes, and nothing since
touched the contract surface.

A minor rather than a patch: collector behaviour changed in ways an integrator
must know about. A reported machine number no longer becomes the PC's asset
number, it builds a controls link instead; a second PC claiming a machine is
treated as a claim rather than a handover; and a backup revision chain is now
per source PC rather than per asset.

CHANGELOG.md

@@ -10,6 +10,16 @@ ADR-007 and ADR-002.
 
 ## [Unreleased]
 
+## [0.9.0] - 2026-08-11
+
+Driven by a fleet that had been failing quietly. A bay had been returning 500
+to every collector report since it was imaged, backups were accumulating
+duplicate revisions on any machine number more than one PC reported against,
+and a setting that looked configurable had never been readable by the script
+that consumed it. The theme of the release is making those failures visible:
+each fix ships with the check, report or document that would have surfaced it.
+
+
 ### Fixed
 
 - A shop-floor PC that reported the machine number of a machine ShopDB already