Merge agent and mode into one (#1689)

The concept of mode has been deprecated, there is now only the agent field in the config.

An agent can be cycled through as your primary agent with <tab> or you can spawn a subagent by @ mentioning it. if you include a description of when to use it, the primary agent will try to automatically use it

Full docs here: https://opencode.ai/docs/agents/

packages/tui/internal/completions/agents.go

@@ -0,0 +1,74 @@
+package completions
+
+import (
+	"context"
+	"log/slog"
+	"strings"
+
+	"github.com/sst/opencode-sdk-go"
+	"github.com/sst/opencode/internal/app"
+	"github.com/sst/opencode/internal/styles"
+	"github.com/sst/opencode/internal/theme"
+)
+
+type agentsContextGroup struct {
+	app *app.App
+}
+
+func (cg *agentsContextGroup) GetId() string {
+	return "agents"
+}
+
+func (cg *agentsContextGroup) GetEmptyMessage() string {
+	return "no matching agents"
+}
+
+func (cg *agentsContextGroup) GetChildEntries(
+	query string,
+) ([]CompletionSuggestion, error) {
+	items := make([]CompletionSuggestion, 0)
+
+	query = strings.TrimSpace(query)
+
+	agents, err := cg.app.Client.App.Agents(
+		context.Background(),
+	)
+	if err != nil {
+		slog.Error("Failed to get agent list", "error", err)
+		return items, err
+	}
+	if agents == nil {
+		return items, nil
+	}
+
+	for _, agent := range *agents {
+		if query != "" && !strings.Contains(strings.ToLower(agent.Name), strings.ToLower(query)) {
+			continue
+		}
+		if agent.Mode == opencode.AgentModePrimary || agent.Name == "general" {
+			continue
+		}
+
+		displayFunc := func(s styles.Style) string {
+			t := theme.CurrentTheme()
+			muted := s.Foreground(t.TextMuted()).Render
+			return s.Render(agent.Name) + muted(" (agent)")
+		}
+
+		item := CompletionSuggestion{
+			Display:    displayFunc,
+			Value:      agent.Name,
+			ProviderID: cg.GetId(),
+			RawData:    agent,
+		}
+		items = append(items, item)
+	}
+
+	return items, nil
+}
+
+func NewAgentsContextGroup(app *app.App) CompletionProvider {
+	return &agentsContextGroup{
+		app: app,
+	}
+}