Add immutable remote commit reader

internal/artifacts/current_state.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"os"
 	"strings"
 
 	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
@@ -44,8 +43,11 @@ type CurrentState struct {
 	SessionPrefix      string
 	CurrentRunIDKey    string
 	CurrentManifestKey string
+	CurrentPointerKey  string
 	RunID              string
 	Manifest           *manifest.Manifest
+	Commit             *RemoteCommitManifest
+	Pointer            *CurrentCommitPointer
 }
 
 type CurrentStateValidation struct {
@@ -55,74 +57,6 @@ type CurrentStateValidation struct {
 	ValidateRunID     bool
 }
 
-func LoadCurrentRunPointer(ctx context.Context, store storage.ObjectStore, currentRunIDKey string) (string, error) {
-	if store == nil {
-		return "", fmt.Errorf("object store is required")
-	}
-	key := strings.TrimSpace(currentRunIDKey)
-	if key == "" {
-		return "", fmt.Errorf("current run pointer key is required")
-	}
-
-	exists, err := store.Exists(ctx, key)
-	if err != nil {
-		return "", fmt.Errorf("check current run pointer %q: %w", key, err)
-	}
-	if !exists {
-		return "", &CurrentRunPointerMissingError{Key: key}
-	}
-
-	localPath, err := storage.DownloadObjectToTemp(ctx, store, key, "narratio-current-run-id-*.txt")
-	if err != nil {
-		return "", fmt.Errorf("download current run pointer %q: %w", key, err)
-	}
-	defer func() { _ = os.Remove(localPath) }()
-
-	data, err := os.ReadFile(localPath)
-	if err != nil {
-		return "", fmt.Errorf("read downloaded current run pointer %q: %w", key, err)
-	}
-	runID := strings.TrimSpace(string(data))
-	if runID == "" {
-		return "", fmt.Errorf("current run pointer %q is empty", key)
-	}
-	if err := ValidateRunIdentity(runID); err != nil {
-		return "", fmt.Errorf("current run pointer %q contains an unsafe legacy run id; migrate remote state before use: %w", key, err)
-	}
-	return runID, nil
-}
-
-func LoadCurrentManifest(ctx context.Context, store storage.ObjectStore, currentManifestKey string) (*manifest.Manifest, error) {
-	if store == nil {
-		return nil, fmt.Errorf("object store is required")
-	}
-	key := strings.TrimSpace(currentManifestKey)
-	if key == "" {
-		return nil, fmt.Errorf("current manifest key is required")
-	}
-
-	exists, err := store.Exists(ctx, key)
-	if err != nil {
-		return nil, fmt.Errorf("check current manifest %q: %w", key, err)
-	}
-	if !exists {
-		return nil, &CurrentManifestMissingError{Key: key}
-	}
-
-	localPath, err := storage.DownloadObjectToTemp(ctx, store, key, "narratio-current-manifest-*.json")
-	if err != nil {
-		return nil, fmt.Errorf("download current manifest %q: %w", key, err)
-	}
-	defer func() { _ = os.Remove(localPath) }()
-
-	manifestStore := &manifest.LocalStore{}
-	m, err := manifestStore.Load(ctx, localPath)
-	if err != nil {
-		return nil, fmt.Errorf("current manifest decode failed: %w", err)
-	}
-	return m, nil
-}
-
 func LoadCurrentState(
 	ctx context.Context,
 	store storage.ObjectStore,
@@ -133,27 +67,19 @@ func LoadCurrentState(
 	if prefix == "" {
 		return nil, fmt.Errorf("session prefix is required")
 	}
-	currentManifestKey, currentRunIDKey := ResolveCurrentStateKeys(prefix)
-	runID, err := LoadCurrentRunPointer(ctx, store, currentRunIDKey)
-	if err != nil {
-		return nil, err
-	}
-	m, err := LoadCurrentManifest(ctx, store, currentManifestKey)
-	if err != nil {
-		return nil, err
+	if store == nil {
+		return nil, fmt.Errorf("object store is required")
 	}
 
-	state := &CurrentState{
-		SessionPrefix:      prefix,
-		CurrentRunIDKey:    currentRunIDKey,
-		CurrentManifestKey: currentManifestKey,
-		RunID:              runID,
-		Manifest:           m,
+	pointerKey := S3CurrentCommitPointerKey(prefix)
+	pointerExists, err := store.Exists(ctx, pointerKey)
+	if err != nil {
+		return nil, fmt.Errorf("check current commit pointer %q: %w", pointerKey, err)
 	}
-	if err := ValidateCurrentStateIdentity(state, validation); err != nil {
-		return nil, err
+	if pointerExists {
+		return loadCommittedCurrentState(ctx, store, prefix, pointerKey, validation)
 	}
-	return state, nil
+	return loadLegacyCurrentState(ctx, store, prefix, validation)
 }
 
 func ValidateCurrentStateIdentity(state *CurrentState, validation CurrentStateValidation) error {