Probe the RPM filename nfpm actually publishes (#175)

nfpm re-renders semver versions into the RPM filename, so `2025.08.03` ships as `2025.8.3`. The existence probe asked artifactapi for the raw metadata version, always got a 404, and rebuilt and republished `nzbget_exporter` and `unkin-ca-certificates` on every pipeline run.

- add `nfpm_rpm_version`/`rpm_file_name` mirroring nfpm rendering
- build the probe filename through `rpm_file_name`
- drop dead `normalize_version` and `get_package_full_name`
- cover the nfpm rendering table and the probed URL in tests

Reviewed-on: #175
Co-authored-by: unkin-agent <unkin-agent@unkin.net>
Co-committed-by: unkin-agent <unkin-agent@unkin.net>

tools/build

@@ -517,37 +517,38 @@ def get_github_token() -> str:
 
 # ==================== GITEA API FUNCTIONS ====================
 
-def normalize_version(version: str) -> str:
+def nfpm_rpm_version(version: str) -> str:
     """
-    Normalize version string by removing leading zeros from numeric components.
-    Gitea automatically does this normalization.
+    Render a metadata version the way nfpm renders it into an RPM filename.
+
+    nfpm re-renders any semver-parseable version: leading zeros are dropped,
+    missing components padded to three, and the prerelease joined with '~'.
+    Anything semver cannot parse (four or more components, non-numeric
+    components, a numeric prerelease identifier with a leading zero) is used
+    verbatim.
 
     Examples:
         "2025.08.03" -> "2025.8.3"
-        "1.05.0" -> "1.5.0"
-        "0.6.1" -> "0.6.1" (no change needed)
-
-    Args:
-        version: Original version string
-
-    Returns:
-        Normalized version string
+        "1.05"       -> "1.5.0"
+        "1.2.3-rc1"  -> "1.2.3~rc1"
+        "1.02.3.4"   -> "1.02.3.4" (not semver, left alone)
     """
-    import re
+    core, sep, prerelease = version.partition('-')
+    if sep and not prerelease:
+        return version
 
-    # Split by common separators and normalize each numeric part
-    parts = re.split(r'([.\-_])', version)
-    normalized_parts = []
+    components = core.split('.')
+    if len(components) > 3 or not all(c.isdigit() for c in components):
+        return version
 
-    for part in parts:
-        # If this part is purely numeric and has leading zeros, remove them
-        if part.isdigit() and len(part) > 1 and part.startswith('0'):
-            # Remove leading zeros but keep at least one digit
-            normalized_parts.append(str(int(part)))
-        else:
-            normalized_parts.append(part)
+    # semver rejects numeric prerelease identifiers with a leading zero
+    if any(i.isdigit() and len(i) > 1 and i.startswith('0')
+           for i in prerelease.split('.')):
+        return version
 
-    return ''.join(normalized_parts)
+    components += ['0'] * (3 - len(components))
+    rendered = '.'.join(str(int(c)) for c in components)
+    return f"{rendered}~{prerelease}" if prerelease else rendered
 
 
 def get_rpm_dist_tag(distro: str) -> str:
@@ -598,6 +599,14 @@ def get_rpm_arch(arch: str) -> str:
     return {'amd64': 'x86_64', 'arm64': 'aarch64'}.get(arch, arch)
 
 
+def rpm_file_name(package_name: str, version: str, release: str, arch: str) -> str:
+    """Filename nfpm produces for this package, and therefore the published name."""
+    return (
+        f"{package_name}-{nfpm_rpm_version(version)}-{release}"
+        f".{get_rpm_arch(arch)}.rpm"
+    )
+
+
 def check_package_exists(
     package_name: str,
     version: str,
@@ -627,7 +636,7 @@ def check_package_exists(
 
     base_url = os.getenv('ARTIFACTAPI_URL', 'https://artifactapi.k8s.syd1.au.unkin.net')
     repo = get_vendor_repo(distro)
-    rpm_file = f"{package_name}-{version}-{release}.{get_rpm_arch(arch)}.rpm"
+    rpm_file = rpm_file_name(package_name, version, release, arch)
     url = f"{base_url}/api/v2/remotes/{repo}/files/Packages/{rpm_file}"
 
     try:
@@ -651,21 +660,6 @@ def check_package_exists(
         return False
 
 
-def get_package_full_name(package_name: str, version: str, release: str) -> str:
-    """
-    Generate the full package name as used in the registry.
-
-    Args:
-        package_name: Package name
-        version: Version string
-        release: Release number
-
-    Returns:
-        Full package name string
-    """
-    return f"{package_name}-{version}-{release}"
-
-
 # ==================== DOCKER FUNCTIONS ====================
 
 def check_docker_available() -> bool: