refactor(config): introduce backend hook system and migrate llama-cpp defaults

Adds RegisterBackendHook/runBackendHooks so each backend can register
default-filling functions that run during ModelConfig.SetDefaults().

Migrates the existing GGUF guessing logic into hooks_llamacpp.go,
registered for both 'llama-cpp' and the empty backend (auto-detect).
Removes the old guesser.go shim.

core/config/backend_hooks.go

@@ -0,0 +1,30 @@
+package config
+
+// BackendDefaultsHook is called during Prepare() and can modify cfg.
+// Only fills in values that are not already set by the user.
+type BackendDefaultsHook func(cfg *ModelConfig, modelPath string)
+
+var backendHooks = map[string][]BackendDefaultsHook{}
+
+// RegisterBackendHook registers a hook for a backend name.
+// Special keys:
+//   - "*"  = global catch-all, runs for EVERY backend (before specific hooks)
+//   - ""   = runs only when cfg.Backend is empty (auto-detect case)
+//   - "vllm", "llama-cpp" etc. = runs only for that specific backend
+//
+// Multiple hooks per key are supported; they run in registration order.
+func RegisterBackendHook(backend string, hook BackendDefaultsHook) {
+	backendHooks[backend] = append(backendHooks[backend], hook)
+}
+
+// runBackendHooks executes hooks in order:
+//  1. "*" (global) hooks for every backend
+//  2. Backend-specific hooks for cfg.Backend (includes "" when backend is empty)
+func runBackendHooks(cfg *ModelConfig, modelPath string) {
+	for _, h := range backendHooks["*"] {
+		h(cfg, modelPath)
+	}
+	for _, h := range backendHooks[cfg.Backend] {
+		h(cfg, modelPath)
+	}
+}

core/config/guesser.go

@@ -1,46 +0,0 @@
-package config
-
-import (
-	"os"
-	"path/filepath"
-
-	gguf "github.com/gpustack/gguf-parser-go"
-	"github.com/mudler/xlog"
-)
-
-func guessDefaultsFromFile(cfg *ModelConfig, modelPath string, defaultCtx int) {
-	if os.Getenv("LOCALAI_DISABLE_GUESSING") == "true" {
-		xlog.Debug("guessDefaultsFromFile: guessing disabled with LOCALAI_DISABLE_GUESSING")
-		return
-	}
-
-	if modelPath == "" {
-		xlog.Debug("guessDefaultsFromFile: modelPath is empty")
-		return
-	}
-
-	// We try to guess only if we don't have a template defined already
-	guessPath := filepath.Join(modelPath, cfg.ModelFileName())
-
-	defer func() {
-		if r := recover(); r != nil {
-			xlog.Error("guessDefaultsFromFile: panic while parsing gguf file")
-		}
-	}()
-
-	defer func() {
-		if cfg.ContextSize == nil {
-			if defaultCtx == 0 {
-				defaultCtx = defaultContextSize
-			}
-			cfg.ContextSize = &defaultCtx
-		}
-	}()
-
-	// try to parse the gguf file
-	f, err := gguf.ParseGGUFFile(guessPath)
-	if err == nil {
-		guessGGUFFromFile(cfg, f, defaultCtx)
-		return
-	}
-}

core/config/hooks_llamacpp.go

@@ -0,0 +1,46 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+
+	gguf "github.com/gpustack/gguf-parser-go"
+	"github.com/mudler/xlog"
+)
+
+func init() {
+	// Register for both explicit llama-cpp and empty backend (auto-detect from GGUF file)
+	RegisterBackendHook("llama-cpp", llamaCppDefaults)
+	RegisterBackendHook("", llamaCppDefaults)
+}
+
+func llamaCppDefaults(cfg *ModelConfig, modelPath string) {
+	if os.Getenv("LOCALAI_DISABLE_GUESSING") == "true" {
+		xlog.Debug("llamaCppDefaults: guessing disabled")
+		return
+	}
+	if modelPath == "" {
+		return
+	}
+
+	guessPath := filepath.Join(modelPath, cfg.ModelFileName())
+
+	defer func() {
+		if r := recover(); r != nil {
+			xlog.Error("llamaCppDefaults: panic while parsing gguf file")
+		}
+	}()
+
+	// Default context size if not set, regardless of whether GGUF parsing succeeds
+	defer func() {
+		if cfg.ContextSize == nil {
+			ctx := defaultContextSize
+			cfg.ContextSize = &ctx
+		}
+	}()
+
+	f, err := gguf.ParseGGUFFile(guessPath)
+	if err == nil {
+		guessGGUFFromFile(cfg, f, 0)
+	}
+}

core/config/model_config.go

@@ -497,7 +497,12 @@ func (cfg *ModelConfig) SetDefaults(opts ...ConfigLoaderOption) {
 		cfg.Debug = &trueV
 	}
 
-	guessDefaultsFromFile(cfg, lo.modelPath, ctx)
+	// If a context size was provided via LoadOptions, apply it before hooks so they
+	// don't override it with their own defaults.
+	if ctx != 0 && cfg.ContextSize == nil {
+		cfg.ContextSize = &ctx
+	}
+	runBackendHooks(cfg, lo.modelPath)
 	cfg.syncKnownUsecasesFromString()
 }