v0.12.1: fast_model for lightweight agents — massive speed boost

- New config field: fast_model — smaller/faster model for lightweight agents
  (reviewer, coordinator, splitter, planner, context, architect, clarifier, etc.)
- Worker, corrector, tester still use main model for quality
- Factory.EffectiveModel routes fast_model to light agents, main model to heavy agents
- Config schema + CLI config set support for fast_model
- AutoFixFormatting: gofmt/ruff auto-fix before QA gate (no LLM needed)
- QA gate: smart skip when no test files, go build check before full tests
- Tester prompt: always JSON, never prose, never attempts file fixes
- Fix: go.mod corruption prevention via focus guard
- All 36 test packages passing

Author: piotrlaczkowski

cmd/slmcode/cmd_util.go

@@ -6,8 +6,8 @@ import (
 	"net/http"
 	"os"
 	"os/exec"
-	"runtime"
 	"path/filepath"
+	"runtime"
 	"strings"
 	"time"
 
@@ -224,6 +224,8 @@ func configCmd() *cobra.Command {
 			switch k {
 			case "model":
 				c.Model = v
+			case "fast_model":
+				c.FastModel = v
 			case "provider":
 				next := config.NormalizeProvider(v)
 				if next != config.NormalizeProvider(c.Provider) && flagEndpoint == "" {

pkg/agents/factory.go

@@ -229,6 +229,7 @@ type Factory struct {
 	Model      string
 	Provider   string
 	CustomDirs []string
+	FastModel  string // optional faster model for lightweight agents
 	// ModelProfiles resolves caps against each agent's effective model
 	// (per-agent override ?? global stack/config model).
 	ModelProfiles map[string]config.ModelProfile
@@ -243,17 +244,32 @@ func NewFactory(llmManager *llm.ProviderManager, toolReg *tools.ToolRegistry, mo
 	return &Factory{LLM: llmManager, Tools: toolReg, Model: model, Provider: provider}
 }
 
-// EffectiveModel returns the model an agent will use (override or global).
+// EffectiveModel returns the model an agent will use (per-agent override → fast model for light agents → global).
 func (f *Factory) EffectiveModel(spec RoleSpec) string {
 	if strings.TrimSpace(spec.Model) != "" {
 		return strings.TrimSpace(spec.Model)
 	}
 	if f == nil {
 		return ""
 	}
+	// Use fast model for lightweight agents that don't need deep reasoning
+	if f.FastModel != "" && isLightAgent(spec.ID) {
+		return f.FastModel
+	}
 	return f.Model
 }
 
+// SetFastModel sets the model for lightweight agents.
+func (f *Factory) SetFastModel(m string) { f.FastModel = m }
+
+var lightAgents = map[string]bool{
+	"reviewer": true, "coordinator": true, "splitter": true, "planner": true,
+	"context": true, "architect": true, "clarifier": true, "interviewer": true,
+	"orchestrator": true, "memory": true, "docs": true, "escalate": true,
+}
+
+func isLightAgent(id string) bool { return lightAgents[strings.ToLower(id)] }
+
 // EffectiveProvider returns the friendly provider name (not registry key).
 func (f *Factory) EffectiveProvider(spec RoleSpec) string {
 	if strings.TrimSpace(spec.Provider) != "" {

pkg/config/config.go

@@ -126,6 +126,10 @@ type Config struct {
 	Endpoint string `yaml:"endpoint" json:"endpoint"`
 	APIKey   string `yaml:"api_key,omitempty" json:"api_key,omitempty"`
 	Model    string `yaml:"model" json:"model"`
+	// FastModel optionally specifies a smaller/faster model for lightweight agents
+	// (reviewer, coordinator, splitter, planner, context, architect, clarifier).
+	// Empty = use the main Model for all agents.
+	FastModel string `yaml:"fast_model" json:"fast_model"`
 
 	Backend string `yaml:"backend" json:"backend"` // slmcode | claude-code
 
@@ -652,6 +656,7 @@ func normalize(c *Config) {
 // Patch is a partial config update. Nil fields are left unchanged.
 type Patch struct {
 	Model                  *string                  `json:"model,omitempty"`
+	FastModel              *string                  `json:"fast_model,omitempty"`
 	Provider               *string                  `json:"provider,omitempty"`
 	Endpoint               *string                  `json:"endpoint,omitempty"`
 	APIKey                 *string                  `json:"api_key,omitempty"`
@@ -726,6 +731,9 @@ func (c *Config) ApplyPatch(p Patch) {
 	if p.Model != nil && *p.Model != "" {
 		c.Model = *p.Model
 	}
+	if p.FastModel != nil {
+		c.FastModel = strings.TrimSpace(*p.FastModel)
+	}
 	prevProvider := NormalizeProvider(c.Provider)
 	prevDefaultEP := DefaultEndpointFor(prevProvider)
 	providerChanged := false

pkg/config/schema.go

@@ -18,6 +18,8 @@ func Schema() []FieldSchema {
 			Description: "LLM provider id (omlx, openai, ollama, …)"},
 		{Key: "model", Type: "string", Label: "Model", Group: "model", Patchable: true,
 			Description: "Default model id"},
+		{Key: "fast_model", Type: "string", Label: "Fast model", Group: "model", Patchable: true,
+			Description: "Smaller model for lightweight agents (reviewer, planner, etc.). Empty = use main model."},
 		{Key: "endpoint", Type: "string", Label: "Endpoint", Group: "model", Patchable: true,
 			Description: "OpenAI-compatible base URL"},
 		{Key: "enabled_models", Type: "string[]", Label: "Enabled models", Group: "model", Patchable: true,

pkg/orchestrator/orchestrator.go

@@ -213,6 +213,10 @@ func New(cfg *config.Config) (*Orchestrator, error) {
 		factory.ProfileMaxTurns = prof.MaxTurns
 		factory.ProfileTemp = prof.Temperature
 	}
+	// Use fast model for lightweight agents when configured
+	if cfg.FastModel != "" {
+		factory.SetFastModel(cfg.FastModel)
+	}
 
 	// Auto-register providers for per-agent overrides (custom agents / builtin patches)
 	// so rebuild never leaves an agent pointing at an unregistered provider.