fix: preserve v prefix for tailscale version

Dockerfile

@@ -21,7 +21,7 @@
 # =============================================================================
 FROM --platform=$BUILDPLATFORM golang:1.26.3-alpine@sha256:91eda9776261207ea25fd06b5b7fed8d397dd2c0a283e77f2ab6e91bfa71079d AS builder
 
-# renovate: datasource=github-releases depName=tailscale packageName=tailscale/tailscale
+# renovate: datasource=github-releases depName=tailscale packageName=tailscale/tailscale versioning=semver
 ARG TAILSCALE_VERSION=v1.98.3
 
 # Provided automatically by buildx for the target platform.

renovate.json

@@ -7,6 +7,17 @@
   ],
   "labels": ["dependencies"],
   "rebaseWhen": "behind-base-branch",
+  "customManagers": [
+    {
+      "customType": "regex",
+      "description": "Update version ARGs annotated with a `# renovate:` comment (the dockerfile manager only handles FROM/image lines, not ARG values).",
+      "managerFilePatterns": ["/(^|/)Dockerfile$/"],
+      "matchStrings": [
+        "#\\s*renovate:\\s*datasource=(?<datasource>\\S+)\\s+depName=(?<depName>\\S+)(?:\\s+packageName=(?<packageName>\\S+))?(?:\\s+versioning=(?<versioning>\\S+))?\\s+ARG \\w+=(?<currentValue>\\S+)"
+      ],
+      "matchStringsStrategy": "any"
+    }
+  ],
   "packageRules": [
     {
       "matchManagers": ["dockerfile"],
@@ -16,9 +27,8 @@
     {
       "matchDatasources": ["github-releases"],
       "matchPackageNames": ["tailscale/tailscale"],
-      "description": "TAILSCALE_VERSION ARG: only stable releases. Tailscale uses EVEN minor versions for stable (v1.98.x); ODD minors (v1.99.x) are unstable, so filter to even minors and ignore pre-releases.",
+      "description": "TAILSCALE_VERSION ARG: only stable releases. Tailscale uses EVEN minor versions for stable (v1.98.x); ODD minors (v1.99.x) are unstable, so filter to even minors and ignore pre-releases. The `v` prefix is kept (no extractVersion) so the ARG value stays v-prefixed to match the git tags cloned in the Dockerfile.",
-      "extractVersion": "^v(?<version>\\d+\\.\\d+\\.\\d+)$",
+      "allowedVersions": "/^v\\d+\\.\\d*[02468]\\.\\d+$/",
-      "allowedVersions": "/^\\d+\\.\\d*[02468]\\.\\d+$/",
       "ignoreUnstable": true
     },
     {
@@ -30,8 +40,15 @@
     },
     {
       "matchManagers": ["dockerfile"],
-      "matchPackageNames": ["golang", "alpine", "busybox"],
+      "matchPackageNames": ["golang", "alpine"],
-      "description": "Automerge PATCH-only bumps of build components (Go/Alpine/busybox) once the PR build passes; review minor/major manually.",
+      "description": "Automerge PATCH-only bumps of build components (Go/Alpine) once the PR build passes; review minor/major manually.",
+      "matchUpdateTypes": ["patch"],
+      "automerge": true
+    },
+    {
+      "matchDatasources": ["docker"],
+      "matchPackageNames": ["busybox"],
+      "description": "busybox ARG (custom manager): automerge PATCH bumps once the PR build passes; review minor/major manually.",
       "matchUpdateTypes": ["patch"],
       "automerge": true
     },