feat(opencode): add runtime agent switching (/agent command + AgentSwitcher) with footer agent display

agent/opencode/agent_list.go

@@ -0,0 +1,137 @@
+package opencode
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"regexp"
+	"sort"
+	"strings"
+	"time"
+)
+
+// agentListTimeout bounds a single `opencode agent list` subprocess call.
+// Mirrors the timeout used by model discovery.
+const agentListTimeout = 10 * time.Second
+
+// AgentMode is the mode reported for an agent by `opencode agent list`.
+type AgentMode string
+
+const (
+	AgentModePrimary  AgentMode = "primary"
+	AgentModeSubagent AgentMode = "subagent"
+	AgentModeAll      AgentMode = "all"
+)
+
+// AgentInfo describes a single agent reported by `opencode agent list`.
+type AgentInfo struct {
+	Name string
+	Mode AgentMode
+}
+
+// agentListLineRe matches a non-indented agent header line from
+// `opencode agent list` output, e.g. "build (primary)".
+var agentListLineRe = regexp.MustCompile(`^(\S+) \((primary|subagent|all)\)$`)
+
+// hiddenAgentNames are opencode internal agents that appear in `opencode
+// agent list` (marked primary) but cannot be selected as a main agent.
+var hiddenAgentNames = map[string]struct{}{
+	"compaction": {},
+	"title":      {},
+	"summary":    {},
+}
+
+// agentValidationSkippedPrefix marks a validation outcome where agent
+// enumeration failed and the check was skipped. Callers log this as
+// "validation skipped" instead of a false "agent invalid" verdict.
+const agentValidationSkippedPrefix = "validation skipped: "
+
+// listAgents runs `opencode agent list` in workDir and parses the output
+// into AgentInfo entries. Internal hidden agents (compaction/title/summary)
+// are excluded; subagent-mode entries are kept so callers can distinguish
+// "exists but is a subagent" from "does not exist". The command is bounded
+// by agentListTimeout. An error is returned when the command fails or no
+// agent line could be parsed (zero matches), so callers degrade gracefully
+// instead of misreporting invalid configuration.
+func listAgents(ctx context.Context, cmd, workDir string) ([]AgentInfo, error) {
+	ctx, cancel := context.WithTimeout(ctx, agentListTimeout)
+	defer cancel()
+
+	c := exec.CommandContext(ctx, cmd, "agent", "list")
+	c.Dir = workDir
+	out, err := c.Output()
+	if err != nil {
+		return nil, fmt.Errorf("opencode: agent list: %w", err)
+	}
+
+	agents := parseAgentListOutput(string(out))
+	if len(agents) == 0 {
+		return nil, fmt.Errorf("opencode: agent list: no parsable agent entries in output")
+	}
+	return agents, nil
+}
+
+// parseAgentListOutput parses `opencode agent list` output: agent header
+// lines are "<name> (<mode>)", followed by an indented permission JSON
+// block that is skipped. Lines that do not match the header format are
+// ignored; a non-empty header line list is always returned.
+func parseAgentListOutput(out string) []AgentInfo {
+	var agents []AgentInfo
+	for _, line := range strings.Split(out, "\n") {
+		if strings.HasPrefix(line, " ") || strings.HasPrefix(line, "\t") {
+			continue
+		}
+		m := agentListLineRe.FindStringSubmatch(line)
+		if m == nil {
+			continue
+		}
+		if _, hidden := hiddenAgentNames[m[1]]; hidden {
+			continue
+		}
+		agents = append(agents, AgentInfo{Name: m[1], Mode: AgentMode(m[2])})
+	}
+	return agents
+}
+
+// ValidateConfiguredAgent checks whether the configured agent is usable as
+// the main agent for the opencode CLI bound to a. An empty configuration is
+// skipped (opencode falls back to its default agent).
+//
+// Return values:
+//   - ("", nil): configuration empty or agent valid (primary/all)
+//   - (problem, available): agent invalid — problem describes the reason and
+//     available lists the usable (non-subagent) agent names
+//   - (problem starting with agentValidationSkippedPrefix, nil): agent
+//     enumeration failed; the check was skipped and nothing can be concluded
+func (a *Agent) ValidateConfiguredAgent(configured string) (problem string, available []string) {
+	if strings.TrimSpace(configured) == "" {
+		return "", nil
+	}
+
+	agents, err := listAgents(context.Background(), a.cmd, a.workDir)
+	if err != nil {
+		return agentValidationSkippedPrefix + err.Error(), nil
+	}
+
+	usable := make([]string, 0, len(agents))
+	mode := AgentMode("")
+	found := false
+	for _, ag := range agents {
+		if ag.Mode != AgentModeSubagent {
+			usable = append(usable, ag.Name)
+		}
+		if ag.Name == configured {
+			found = true
+			mode = ag.Mode
+		}
+	}
+	sort.Strings(usable)
+
+	if !found {
+		return fmt.Sprintf("agent %q does not exist", configured), usable
+	}
+	if mode == AgentModeSubagent {
+		return fmt.Sprintf("agent %q is a subagent and cannot be used as the main agent", configured), usable
+	}
+	return "", nil
+}