feat(agent): support reasoning effort configuration

Author: lvillani

internal/agent/agent.go

@@ -78,10 +78,11 @@ func NewAgent(m Model, cfg config.Config, reg ...*skills.Registry) (*Agent, erro
 		ModelInfo: findModel(cfg.Model),
 		skills:    skillsRegistry,
 		Chat: model.Chat{
-			Model:     cfg.Model,
-			SessionID: model.NewSessionID(),
-			Messages:  []model.Message{{Role: model.MessageRoleDeveloper, Content: developerPrompt}},
-			Tools:     toolRegistry.Tools(),
+			Model:           cfg.Model,
+			ReasoningEffort: cfg.ReasoningEffort,
+			SessionID:       model.NewSessionID(),
+			Messages:        []model.Message{{Role: model.MessageRoleDeveloper, Content: developerPrompt}},
+			Tools:           toolRegistry.Tools(),
 		},
 	}, nil
 }

internal/config/config.go

@@ -4,16 +4,20 @@
 package config
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/adrg/xdg"
 	"github.com/pelletier/go-toml/v2"
+
+	"thing/internal/model"
 )
 
 // Config represents the configuration for the application.
 type Config struct {
-	Model    string `toml:"model"`
-	Endpoint string `toml:"endpoint"`
+	Model           string                `toml:"model"`
+	Endpoint        string                `toml:"endpoint"`
+	ReasoningEffort model.ReasoningEffort `toml:"reasoning_effort"`
 }
 
 // Load loads the configuration file from the XDG config directory.
@@ -33,6 +37,9 @@ func Load() (*Config, error) {
 	if err := toml.NewDecoder(f).Decode(&config); err != nil {
 		return nil, err
 	}
+	if config.ReasoningEffort != "" && !config.ReasoningEffort.Valid() {
+		return nil, fmt.Errorf("invalid reasoning_effort %q: want minimal, low, medium, high, xhigh, or max", config.ReasoningEffort)
+	}
 
 	return &config, nil
 }

internal/model/model.go

@@ -12,6 +12,30 @@ import (
 // MessageRole represents the role of a message in a chat conversation.
 type MessageRole string
 
+// ReasoningEffort controls how many reasoning tokens the model may use.
+// OpenAI defines these values for reasoning-capable models.
+type ReasoningEffort string
+
+const (
+	ReasoningEffortMinimal ReasoningEffort = "minimal"
+	ReasoningEffortLow     ReasoningEffort = "low"
+	ReasoningEffortMedium  ReasoningEffort = "medium"
+	ReasoningEffortHigh    ReasoningEffort = "high"
+	ReasoningEffortXHigh   ReasoningEffort = "xhigh"
+	ReasoningEffortMax     ReasoningEffort = "max"
+)
+
+// Valid reports whether the reasoning effort is an OpenAI-supported value.
+func (r ReasoningEffort) Valid() bool {
+	switch r {
+	case ReasoningEffortMinimal, ReasoningEffortLow, ReasoningEffortMedium,
+		ReasoningEffortHigh, ReasoningEffortXHigh, ReasoningEffortMax:
+		return true
+	default:
+		return false
+	}
+}
+
 const (
 	MessageRoleDeveloper MessageRole = "developer" // Developer-provided instructions that the model should follow.
 	MessageRoleUser      MessageRole = "user"      // Messages sent by an end user.
@@ -32,10 +56,11 @@ const (
 // together to maximize cache hits. Keeping it here means it serializes with the
 // conversation and so is restored naturally when deserializing it.
 type Chat struct {
-	SessionID string    `json:"session_id,omitempty"`
-	Model     string    `json:"model"`
-	Tools     []Tool    `json:"tools"`
-	Messages  []Message `json:"messages"`
+	SessionID       string          `json:"session_id,omitempty"`
+	Model           string          `json:"model"`
+	ReasoningEffort ReasoningEffort `json:"reasoning_effort,omitempty"`
+	Tools           []Tool          `json:"tools"`
+	Messages        []Message       `json:"messages"`
 }
 
 // NewSessionID returns a random UUIDv4 used to identify a conversation.