fix(standalone): use SDK genesis provider to handle AppGenesis format

The standalone binary was failing to start with the error:
"invalid 64-bit integer encoding '1', expected string"

This was caused by using node.DefaultGenesisDocProviderFunc which reads
the genesis file directly as CometBFT's GenesisDoc format, but the SDK's
init command generates an AppGenesis file where InitialHeight is an int64
(serialized as a JSON integer) rather than a string.

This commit adds a custom getGenDocProvider function that:
1. Reads the genesis file using the SDK's AppGenesisFromFile
2. Converts it to CometBFT's GenesisDoc using ToGenesisDoc()

This matches the pattern used by the multiplexer binary in
multiplexer/internal/utils.go:GetGenDocProvider.

Closes #164

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: rootulp

cmd/celestia-appd/cmd/start_command_standalone.go

@@ -19,6 +19,7 @@ import (
 	"github.com/cometbft/cometbft/proxy"
 	"github.com/cometbft/cometbft/rpc/client/local"
 	coregrpc "github.com/cometbft/cometbft/rpc/grpc"
+	cmttypes "github.com/cometbft/cometbft/types"
 	db "github.com/cosmos/cosmos-db"
 	"github.com/cosmos/cosmos-sdk/client"
 	"github.com/cosmos/cosmos-sdk/server"
@@ -28,6 +29,7 @@ import (
 	servercmtlog "github.com/cosmos/cosmos-sdk/server/log"
 	servertypes "github.com/cosmos/cosmos-sdk/server/types"
 	"github.com/cosmos/cosmos-sdk/telemetry"
+	genutiltypes "github.com/cosmos/cosmos-sdk/x/genutil/types"
 	"golang.org/x/sync/errgroup"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials/insecure"
@@ -173,7 +175,7 @@ func startCometNode(svrCtx *server.Context, appInstance servertypes.Application)
 		privVal,
 		nodeKey,
 		proxy.NewLocalClientCreator(cmtApp),
-		node.DefaultGenesisDocProviderFunc(cfg),
+		getGenDocProvider(cfg),
 		cmtcfg.DefaultDBProvider,
 		node.DefaultMetricsProvider(cfg.Instrumentation),
 		servercmtlog.CometLoggerWrapper{Logger: svrCtx.Logger},
@@ -341,3 +343,16 @@ func openDB(rootDir string, backendType db.BackendType) (db.DB, error) {
 	dataDir := filepath.Join(rootDir, "data")
 	return db.NewDB("application", backendType, dataDir)
 }
+
+// getGenDocProvider returns a function that loads the genesis document from file.
+// This uses the SDK's AppGenesis format and converts it to CometBFT's GenesisDoc,
+// which properly handles the type conversion (e.g., InitialHeight as int64 vs string).
+func getGenDocProvider(cfg *cmtcfg.Config) func() (*cmttypes.GenesisDoc, error) {
+	return func() (*cmttypes.GenesisDoc, error) {
+		appGenesis, err := genutiltypes.AppGenesisFromFile(cfg.GenesisFile())
+		if err != nil {
+			return nil, err
+		}
+		return appGenesis.ToGenesisDoc()
+	}
+}

cmd/celestia-appd/cmd/start_command_standalone_test.go

@@ -0,0 +1,75 @@
+//go:build !multiplexer
+
+package cmd
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	cmtcfg "github.com/cometbft/cometbft/config"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetGenDocProvider(t *testing.T) {
+	// Create a temporary directory for the test
+	tempDir := t.TempDir()
+	configDir := filepath.Join(tempDir, "config")
+	require.NoError(t, os.MkdirAll(configDir, 0o755))
+
+	// Create a genesis file in SDK AppGenesis format (with InitialHeight as integer)
+	genesisFile := filepath.Join(configDir, "genesis.json")
+	// This is the format that the SDK's init command generates
+	genesisContent := `{
+		"app_name": "celestia-appd",
+		"app_version": "test",
+		"genesis_time": "2024-01-01T00:00:00Z",
+		"chain_id": "test-chain",
+		"initial_height": 1,
+		"app_hash": null,
+		"app_state": {},
+		"consensus": {
+			"validators": [],
+			"params": {
+				"block": {"max_bytes": "22020096", "max_gas": "-1"},
+				"evidence": {"max_age_num_blocks": "100000", "max_age_duration": "172800000000000", "max_bytes": "1048576"},
+				"validator": {"pub_key_types": ["ed25519"]},
+				"version": {"app": "0"},
+				"abci": {"vote_extensions_enable_height": "0"}
+			}
+		}
+	}`
+	require.NoError(t, os.WriteFile(genesisFile, []byte(genesisContent), 0o644))
+
+	// Create a CometBFT config pointing to the temp directory
+	cfg := cmtcfg.DefaultConfig()
+	cfg.SetRoot(tempDir)
+
+	// Get the genesis doc provider and call it
+	provider := getGenDocProvider(cfg)
+	genDoc, err := provider()
+
+	// Verify no error occurred (this would fail with the old DefaultGenesisDocProviderFunc
+	// because it can't handle InitialHeight as an integer)
+	require.NoError(t, err)
+
+	// Verify the genesis doc was parsed correctly
+	assert.Equal(t, "test-chain", genDoc.ChainID)
+	assert.Equal(t, int64(1), genDoc.InitialHeight)
+	assert.Equal(t, time.Date(2024, 1, 1, 0, 0, 0, 0, time.UTC), genDoc.GenesisTime)
+}
+
+func TestGetGenDocProvider_FileNotFound(t *testing.T) {
+	// Create a CometBFT config pointing to a non-existent directory
+	cfg := cmtcfg.DefaultConfig()
+	cfg.SetRoot("/non/existent/path")
+
+	// Get the genesis doc provider and call it
+	provider := getGenDocProvider(cfg)
+	_, err := provider()
+
+	// Verify an error occurred
+	assert.Error(t, err)
+}