renovate: let the nginx constraint survive a variant tag

The anchored form rejected any tag with a suffix. Docker versioning only
offers candidates carrying the current tag's suffix, so the day the
delegation sidecar moves to a slimmer base image (#84, still open) every
candidate would fail the filter and nginx would stop receiving updates -
without an error, a warning, or a red dashboard.

Verified against currentValue 1.28.0-alpine: anchored form returns
"updates": [] and "warnings": [], the suffix-tolerant form proposes
1.30.4-alpine and still refuses the newer 1.31.x mainline.

README.md

@@ -70,7 +70,7 @@ What Renovate keeps current:
 
 Each chart renders its main image as `<repo>:{{ .Chart.AppVersion }}` — repository in the template, version in `Chart.yaml`. Renovate cannot join two files, so the mapping lives in `renovate.json5`, one block per chart. It is deliberately *not* a `# renovate:` comment inside each `Chart.yaml`: that would touch all chart directories and force a version bump plus a publish per chart for a pure comment change. Charts whose tags carry a flavour or date suffix (`apache-tika`, `minecraft-server`, `rss-bridge`, `teamspeak-server`) override `versioning` in their block; the reasoning sits next to each one.
 
-One dependency is constrained beyond its versioning: **nginx** (the Synapse delegation sidecar) is limited to **even minors** via `allowedVersions`. nginx numbers its release branches by minor — even is stable, odd is mainline — and the chart belongs on stable. Patch updates inside the stable branch still flow through normally.
+One dependency is constrained beyond its versioning: **nginx** (the Synapse delegation sidecar) is limited to **even minors** via `allowedVersions`. nginx numbers its release branches by minor — even is stable, odd is mainline — and the chart belongs on stable. Patch updates inside the stable branch still flow through normally. The constraint tolerates a variant suffix (`1.30.4-alpine`) on purpose: docker versioning only ever offers candidates carrying the current tag's suffix, so a suffix-blind constraint would silently freeze nginx the day the sidecar moves to a slimmer base image (#84) — no error, no warning.
 
 Not managed: `ci/**` (install-test fixtures pin throwaway infrastructure to major lines on purpose) and `template-chart/**` (placeholder image). A consequence worth knowing: `ci/matrix-synapse/fixtures.yaml` pins a Synapse image that Renovate will not follow — bump it by hand when the chart moves a major.
 

renovate.json5

@@ -108,8 +108,15 @@
       matchDatasources: ["docker"],
       matchPackageNames: ["nginx", "library/nginx", "docker.io/library/nginx"],
       // Even minor: any minor whose last digit is even, so 1.30.x passes and
-      // 1.31.x does not.
+      // 1.31.x does not. The trailing (-.+)? is load-bearing: #84 proposes
-      allowedVersions: "/^\\d+\\.\\d*[02468]\\.\\d+$/",
+      // moving this sidecar to a slimmer base image, and with a variant tag
+      // like 1.30.4-alpine docker versioning only ever offers candidates
+      // carrying the same suffix. Without the optional suffix, every one of
+      // them would fail this filter and nginx would silently stop receiving
+      // updates - no error, no warning, green dashboard. Verified: with the
+      // anchored form and currentValue 1.28.0-alpine, the lookup returns
+      // "updates": [] and "warnings": [].
+      allowedVersions: "/^\\d+\\.\\d*[02468]\\.\\d+(-.+)?$/",
     },
   ],