fix: add default cases to switch statements for model format handling

Author: ilopezluna

AGENTS.md

@@ -23,6 +23,14 @@ If any step fails, fix the issue and re-run before committing.
 - **golangci-lint v2.7.2+** — [Install instructions](https://golangci-lint.run/welcome/install/)
 - **ShellCheck** — `brew install shellcheck` (macOS) or `apt-get install shellcheck` (Linux)
 
+## Linting
+
+- **Never use `//nolint:exhaustive`** to suppress the `exhaustive` linter.
+  Instead, always cover all cases in `switch` statements on enum types — either
+  by listing every value explicitly or by including a `default:` branch. This
+  ensures that when a new value is added to the enum, the linter flags any
+  switch that doesn't handle it, preventing silent bugs.
+
 ## Testing
 
 When adding a new Go package that contains tests, include a

pkg/distribution/internal/partial/partial.go

@@ -238,7 +238,6 @@ func matchesMediaType(layerMT, targetMT oci.MediaType, modelFormat string) bool
 	}
 
 	// Native ModelPack support: check format-specific ModelPack types
-	//nolint:exhaustive // Only GGUF and Safetensors need cross-format matching
 	switch targetMT {
 	case types.MediaTypeGGUF:
 		if layerMT == modelpack.MediaTypeWeightGGUF {
@@ -248,6 +247,8 @@ func matchesMediaType(layerMT, targetMT oci.MediaType, modelFormat string) bool
 		if layerMT == modelpack.MediaTypeWeightSafetensors {
 			return true
 		}
+	default:
+		// No format-specific ModelPack mapping for this media type
 	}
 
 	// ModelPack model-spec support: format-agnostic weight types (.raw, .tar, etc.)
@@ -256,14 +257,15 @@ func matchesMediaType(layerMT, targetMT oci.MediaType, modelFormat string) bool
 	// in their media type and are handled above; applying this fallback to them would
 	// cause cross-format false positives (e.g., safetensors layer matching as GGUF).
 	if modelFormat != "" && modelpack.IsModelPackGenericWeightMediaType(string(layerMT)) {
-		//nolint:exhaustive // Only weight formats need cross-format matching
 		switch targetMT {
 		case types.MediaTypeGGUF:
 			return modelFormat == string(types.FormatGGUF)
 		case types.MediaTypeSafetensors:
 			return modelFormat == string(types.FormatSafetensors)
 		case types.MediaTypeDDUF:
 			return modelFormat == string(types.FormatDDUF) || modelFormat == string(types.FormatDiffusers) //nolint:staticcheck // FormatDiffusers kept for backward compatibility
+		default:
+			// No generic weight resolution for this media type
 		}
 	}