feat(cmd/server): support reading initial prompt from stdin

cmd/server/server.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"log/slog"
 	"net/http"
 	"os"
@@ -70,6 +71,11 @@ func parseAgentType(firstArg string, agentTypeVar string) (AgentType, error) {
 	return AgentTypeCustom, nil
 }
 
+// isStdinPiped checks if stdin is piped (not a terminal)
+func isStdinPiped(stat os.FileInfo) bool {
+	return (stat.Mode() & os.ModeCharDevice) == 0
+}
+
 func runServer(ctx context.Context, logger *slog.Logger, argsToPass []string) error {
 	agent := argsToPass[0]
 	agentTypeValue := viper.GetString(FlagType)
@@ -88,6 +94,19 @@ func runServer(ctx context.Context, logger *slog.Logger, argsToPass []string) er
 		return xerrors.Errorf("term height must be at least 10")
 	}
 
+	// Read stdin if it's piped, to be used as initial prompt
+	initialPrompt := viper.GetString(FlagInitialPrompt)
+	if initialPrompt == "" {
+		if stat, err := os.Stdin.Stat(); err == nil && isStdinPiped(stat) {
+			if stdinData, err := io.ReadAll(os.Stdin); err != nil {
+				return xerrors.Errorf("failed to read stdin: %w", err)
+			} else if len(stdinData) > 0 {
+				initialPrompt = string(stdinData)
+				logger.Info("Read initial prompt from stdin", "bytes", len(stdinData))
+			}
+		}
+	}
+
 	printOpenAPI := viper.GetBool(FlagPrintOpenAPI)
 	var process *termexec.Process
 	if printOpenAPI {
@@ -112,7 +131,7 @@ func runServer(ctx context.Context, logger *slog.Logger, argsToPass []string) er
 		ChatBasePath:   viper.GetString(FlagChatBasePath),
 		AllowedHosts:   viper.GetStringSlice(FlagAllowedHosts),
 		AllowedOrigins: viper.GetStringSlice(FlagAllowedOrigins),
-		InitialPrompt:  viper.GetString(FlagInitialPrompt),
+		InitialPrompt:  initialPrompt,
 	})
 	if err != nil {
 		return xerrors.Errorf("failed to create server: %w", err)
@@ -213,7 +232,7 @@ func CreateServerCmd() *cobra.Command {
 		{FlagAllowedHosts, "a", []string{"localhost", "127.0.0.1", "[::1]"}, "HTTP allowed hosts (hostnames only, no ports). Use '*' for all, comma-separated list via flag, space-separated list via AGENTAPI_ALLOWED_HOSTS env var", "stringSlice"},
 		// localhost:3284 is the default origin when you open the chat interface in your browser. localhost:3000 and 3001 are used during development.
 		{FlagAllowedOrigins, "o", []string{"http://localhost:3284", "http://localhost:3000", "http://localhost:3001"}, "HTTP allowed origins. Use '*' for all, comma-separated list via flag, space-separated list via AGENTAPI_ALLOWED_ORIGINS env var", "stringSlice"},
-		{FlagInitialPrompt, "I", "", "Initial prompt for the agent (recommended only if the agent doesn't support initial prompt in interaction mode)", "string"},
+		{FlagInitialPrompt, "I", "", "Initial prompt for the agent. Recommended only if the agent doesn't support initial prompt in interaction mode. Will be read from stdin if piped (e.g., echo 'prompt' | agentapi server -- my-agent)", "string"},
 	}
 
 	for _, spec := range flagSpecs {

cmd/server/server_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
@@ -571,3 +572,46 @@ func TestServerCmd_AllowedOrigins(t *testing.T) {
 		})
 	}
 }
+
+func TestIsStdinPiped(t *testing.T) {
+	tests := []struct {
+		name     string
+		fileInfo os.FileInfo
+		expected bool
+	}{
+		{
+			name:     "regular file (piped)",
+			fileInfo: &mockFileInfo{mode: 0},
+			expected: true,
+		},
+		{
+			name:     "character device (terminal)",
+			fileInfo: &mockFileInfo{mode: os.ModeCharDevice},
+			expected: false,
+		},
+		{
+			name:     "named pipe",
+			fileInfo: &mockFileInfo{mode: os.ModeNamedPipe},
+			expected: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isStdinPiped(tt.fileInfo)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
+// mockFileInfo implements os.FileInfo for testing
+type mockFileInfo struct {
+	mode os.FileMode
+}
+
+func (m *mockFileInfo) Name() string       { return "stdin" }
+func (m *mockFileInfo) Size() int64        { return 0 }
+func (m *mockFileInfo) Mode() os.FileMode  { return m.mode }
+func (m *mockFileInfo) ModTime() time.Time { return time.Time{} }
+func (m *mockFileInfo) IsDir() bool        { return false }
+func (m *mockFileInfo) Sys() interface{}   { return nil }