Add prepare helper to hydrate previous-session artifacts from archive

internal/stage/prepare_previous.go

@@ -0,0 +1,475 @@
+package stage
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
+)
+
+const (
+	preparePreviousInputKindManifest = "previous_manifest"
+	preparePreviousInputKindArtifact = "previous_artifact"
+	preparePreviousInputSource       = "previous_session_archive.current"
+)
+
+// previousSessionHydrationResult captures prepare-time previous-session cache materialization.
+type previousSessionHydrationResult struct {
+	Inputs         []manifest.InputRecord
+	Hydrated       []string
+	SkippedMissing []string
+	PreviousRunID  string
+}
+
+func hydratePreviousSessionArtifacts(
+	ctx context.Context,
+	env *Env,
+	paths artifacts.SessionPaths,
+	requirements []artifacts.PreviousArtifactRequirement,
+) (*previousSessionHydrationResult, error) {
+	if len(requirements) == 0 {
+		return &previousSessionHydrationResult{}, nil
+	}
+	if env == nil || env.Config == nil || env.Config.Session == nil || env.Config.Pipeline == nil {
+		return nil, fmt.Errorf("resolved config with session/pipeline is required")
+	}
+	if env.ArtifactStore == nil {
+		return nil, fmt.Errorf("artifact store is required")
+	}
+
+	orderedRequirements := append([]artifacts.PreviousArtifactRequirement(nil), requirements...)
+	sort.Slice(orderedRequirements, func(i, j int) bool {
+		return orderedRequirements[i].Name < orderedRequirements[j].Name
+	})
+
+	requiredNames := requiredPreviousArtifactNames(orderedRequirements)
+	optionalNames := optionalPreviousArtifactNames(orderedRequirements)
+	previousSessionID := strings.TrimSpace(env.Config.Session.PreviousSessionID)
+	if previousSessionID == "" {
+		if len(requiredNames) > 0 {
+			return nil, fmt.Errorf(
+				"previous_session_id is required for required previous-session artifacts: %s",
+				strings.Join(requiredNames, ", "),
+			)
+		}
+		return &previousSessionHydrationResult{SkippedMissing: optionalNames}, nil
+	}
+
+	if env.ObjectStore == nil {
+		return nil, fmt.Errorf("previous-session artifact hydration requires object store backend")
+	}
+	if env.Config.Pipeline.Storage.S3 == nil {
+		return nil, fmt.Errorf("pipeline.storage.s3 configuration is required for previous-session artifact hydration")
+	}
+	campaign := strings.TrimSpace(env.Config.Session.Campaign)
+	if campaign == "" {
+		return nil, fmt.Errorf("session campaign is required for previous-session artifact hydration")
+	}
+	bucket := strings.TrimSpace(env.Config.Pipeline.Storage.S3.Bucket)
+	if bucket == "" {
+		return nil, fmt.Errorf("pipeline.storage.s3.bucket is required for previous-session artifact hydration")
+	}
+
+	previousSessionPrefix := artifacts.S3SessionPrefix(
+		env.Config.Pipeline.Storage.S3.RootPrefix,
+		campaign,
+		previousSessionID,
+	)
+	currentManifestKey, currentRunIDKey := artifacts.ResolveArchiveCurrentStateKeys(previousSessionPrefix)
+
+	result := &previousSessionHydrationResult{}
+
+	runPointerExists, err := env.ObjectStore.Exists(ctx, currentRunIDKey)
+	if err != nil {
+		return nil, fmt.Errorf("check previous-session current run pointer %q: %w", currentRunIDKey, err)
+	}
+	if !runPointerExists {
+		if len(requiredNames) > 0 {
+			return nil, fmt.Errorf("required previous-session artifacts unavailable: remote current run pointer missing: %q", currentRunIDKey)
+		}
+		result.SkippedMissing = optionalNames
+		return result, nil
+	}
+
+	runIDTemp, err := downloadObjectToTempStage(ctx, env.ObjectStore, currentRunIDKey, "narratio-prepare-previous-run-id-*.txt")
+	if err != nil {
+		return nil, fmt.Errorf("download previous-session current run pointer %q: %w", currentRunIDKey, err)
+	}
+	defer func() { _ = os.Remove(runIDTemp) }()
+
+	runIDBytes, err := os.ReadFile(runIDTemp)
+	if err != nil {
+		return nil, fmt.Errorf("read previous-session current run pointer %q: %w", currentRunIDKey, err)
+	}
+	previousRunID := strings.TrimSpace(string(runIDBytes))
+	if previousRunID == "" {
+		return nil, fmt.Errorf("previous-session current run pointer %q is empty", currentRunIDKey)
+	}
+	result.PreviousRunID = previousRunID
+
+	manifestExists, err := env.ObjectStore.Exists(ctx, currentManifestKey)
+	if err != nil {
+		return nil, fmt.Errorf("check previous-session current manifest %q: %w", currentManifestKey, err)
+	}
+	if !manifestExists {
+		if len(requiredNames) > 0 {
+			return nil, fmt.Errorf("required previous-session artifacts unavailable: remote current manifest missing: %q", currentManifestKey)
+		}
+		result.SkippedMissing = optionalNames
+		return result, nil
+	}
+
+	if err := os.MkdirAll(filepath.Dir(paths.PreviousManifestPath), 0o755); err != nil {
+		return nil, fmt.Errorf("create previous manifest directory: %w", err)
+	}
+	if err := env.ObjectStore.Download(ctx, currentManifestKey, paths.PreviousManifestPath); err != nil {
+		return nil, fmt.Errorf("download previous-session current manifest %q: %w", currentManifestKey, err)
+	}
+
+	manifestStore := &manifest.LocalStore{}
+	previousManifest, err := manifestStore.Load(ctx, paths.PreviousManifestPath)
+	if err != nil {
+		return nil, fmt.Errorf("decode downloaded previous-session manifest %q: %w", currentManifestKey, err)
+	}
+	if strings.TrimSpace(previousManifest.SessionID) != previousSessionID {
+		return nil, fmt.Errorf(
+			"previous-session manifest session_id %q does not match configured previous_session_id %q",
+			strings.TrimSpace(previousManifest.SessionID),
+			previousSessionID,
+		)
+	}
+	if strings.TrimSpace(previousManifest.Campaign) != campaign {
+		return nil, fmt.Errorf(
+			"previous-session manifest campaign %q does not match current campaign %q",
+			strings.TrimSpace(previousManifest.Campaign),
+			campaign,
+		)
+	}
+	if strings.TrimSpace(previousManifest.RunID) == "" {
+		return nil, fmt.Errorf("previous-session manifest run_id is required")
+	}
+	if strings.TrimSpace(previousManifest.RunID) != previousRunID {
+		return nil, fmt.Errorf(
+			"previous-session current run pointer %q references run %q but current manifest run_id is %q",
+			currentRunIDKey,
+			previousRunID,
+			strings.TrimSpace(previousManifest.RunID),
+		)
+	}
+
+	manifestChecksum, err := env.ArtifactStore.Checksum(paths.PreviousManifestPath)
+	if err != nil {
+		return nil, fmt.Errorf("checksum downloaded previous-session manifest: %w", err)
+	}
+	result.Inputs = append(result.Inputs, manifest.InputRecord{
+		Kind:     preparePreviousInputKindManifest,
+		Path:     paths.PreviousManifestPath,
+		Checksum: manifestChecksum,
+		Source:   preparePreviousInputSource,
+		S3Bucket: bucket,
+		S3Key:    currentManifestKey,
+	})
+
+	for _, requirement := range orderedRequirements {
+		candidates := previousArtifactRelativePathCandidates(requirement.Name, previousManifest, env.Config)
+		if len(candidates) == 0 {
+			if requirement.Required {
+				return nil, fmt.Errorf(
+					"required previous-session artifact %q is unavailable in previous-session manifest/archive",
+					requirement.Name,
+				)
+			}
+			result.SkippedMissing = append(result.SkippedMissing, requirement.Name)
+			continue
+		}
+
+		selectedRel := ""
+		selectedKey := ""
+		for _, candidate := range candidates {
+			remoteKey := artifacts.S3PromotedArtifactKey(previousSessionPrefix, candidate)
+			exists, err := env.ObjectStore.Exists(ctx, remoteKey)
+			if err != nil {
+				return nil, fmt.Errorf("check previous-session artifact object %q: %w", remoteKey, err)
+			}
+			if !exists {
+				continue
+			}
+			selectedRel = candidate
+			selectedKey = remoteKey
+			break
+		}
+		if selectedRel == "" {
+			if requirement.Required {
+				return nil, fmt.Errorf(
+					"required previous-session artifact %q object missing from archive candidate keys",
+					requirement.Name,
+				)
+			}
+			result.SkippedMissing = append(result.SkippedMissing, requirement.Name)
+			continue
+		}
+
+		localPath := artifacts.SessionPreviousArtifactPath(paths, selectedRel)
+		if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
+			return nil, fmt.Errorf("create previous-session artifact directory for %q: %w", localPath, err)
+		}
+		if err := env.ObjectStore.Download(ctx, selectedKey, localPath); err != nil {
+			return nil, fmt.Errorf("download previous-session artifact %q from %q: %w", requirement.Name, selectedKey, err)
+		}
+		if err := requireNonEmptyFile(localPath, "previous-session artifact "+requirement.Name); err != nil {
+			return nil, err
+		}
+		checksum, err := env.ArtifactStore.Checksum(localPath)
+		if err != nil {
+			return nil, fmt.Errorf("checksum previous-session artifact %q: %w", requirement.Name, err)
+		}
+
+		result.Inputs = append(result.Inputs, manifest.InputRecord{
+			Kind:     preparePreviousInputKindArtifact,
+			Path:     localPath,
+			Checksum: checksum,
+			Source:   preparePreviousInputSource,
+			S3Bucket: bucket,
+			S3Key:    selectedKey,
+		})
+		result.Hydrated = append(result.Hydrated, requirement.Name)
+	}
+
+	sort.Strings(result.Hydrated)
+	sort.Strings(result.SkippedMissing)
+	sort.Slice(result.Inputs, func(i, j int) bool {
+		if result.Inputs[i].Kind != result.Inputs[j].Kind {
+			return result.Inputs[i].Kind < result.Inputs[j].Kind
+		}
+		return result.Inputs[i].Path < result.Inputs[j].Path
+	})
+	return result, nil
+}
+
+func requiredPreviousArtifactNames(requirements []artifacts.PreviousArtifactRequirement) []string {
+	names := make([]string, 0, len(requirements))
+	for _, requirement := range requirements {
+		if requirement.Required {
+			names = append(names, strings.TrimSpace(requirement.Name))
+		}
+	}
+	sort.Strings(names)
+	return names
+}
+
+func optionalPreviousArtifactNames(requirements []artifacts.PreviousArtifactRequirement) []string {
+	names := make([]string, 0, len(requirements))
+	for _, requirement := range requirements {
+		if requirement.Required {
+			continue
+		}
+		names = append(names, strings.TrimSpace(requirement.Name))
+	}
+	sort.Strings(names)
+	return names
+}
+
+func previousArtifactRelativePathCandidates(
+	artifactName string,
+	previousManifest *manifest.Manifest,
+	cfg *config.Config,
+) []string {
+	candidates := []string{}
+	appendCandidate := func(v string) {
+		normalized, err := normalizeArchiveRelativePath(v)
+		if err != nil {
+			return
+		}
+		candidates = append(candidates, normalized)
+	}
+
+	sourceID := artifacts.ConfiguredArtifactSourceID(artifactName)
+	if rel, ok := previousManifestArtifactRelativePathBySourceID(previousManifest, sourceID); ok {
+		appendCandidate(rel)
+		base := path.Base(rel)
+		for _, promoted := range previousManifestPromotedPaths(previousManifest) {
+			if path.Base(promoted) == base {
+				appendCandidate(promoted)
+			}
+		}
+	}
+
+	if cfg != nil && cfg.Pipeline != nil && cfg.Pipeline.Scriptorium != nil {
+		if artifactCfg, ok := cfg.Pipeline.Scriptorium.Artifacts[artifactName]; ok {
+			appendCandidate(artifactCfg.OutputPath)
+		}
+	}
+
+	return dedupeOrderedStrings(candidates)
+}
+
+func previousManifestArtifactRelativePathBySourceID(previousManifest *manifest.Manifest, sourceID string) (string, bool) {
+	if previousManifest == nil || len(previousManifest.Stages) == 0 {
+		return "", false
+	}
+	sourceID = strings.TrimSpace(sourceID)
+	if sourceID == "" {
+		return "", false
+	}
+
+	stageNames := make([]string, 0, len(previousManifest.Stages))
+	if _, ok := previousManifest.Stages["analyze"]; ok {
+		stageNames = append(stageNames, "analyze")
+	}
+	for stageName := range previousManifest.Stages {
+		if stageName == "analyze" {
+			continue
+		}
+		stageNames = append(stageNames, stageName)
+	}
+	start := 0
+	if len(stageNames) > 0 && stageNames[0] == "analyze" {
+		start = 1
+	}
+	sort.Strings(stageNames[start:])
+
+	for _, stageName := range stageNames {
+		sr := previousManifest.Stages[stageName]
+		if sr == nil {
+			continue
+		}
+		for _, out := range sr.Outputs {
+			if strings.TrimSpace(out.SourceID) != sourceID {
+				continue
+			}
+			rel, ok := derivePreviousManifestRelativePath(previousManifest, out.LocalPath)
+			if ok {
+				return rel, true
+			}
+		}
+	}
+	return "", false
+}
+
+func derivePreviousManifestRelativePath(previousManifest *manifest.Manifest, localPath string) (string, bool) {
+	trimmed := strings.TrimSpace(localPath)
+	if trimmed == "" {
+		return "", false
+	}
+	if !filepath.IsAbs(trimmed) {
+		normalized, err := normalizeArchiveRelativePath(filepath.ToSlash(trimmed))
+		if err != nil {
+			return "", false
+		}
+		return normalized, true
+	}
+
+	sessionRoot, ok := previousManifestSessionRoot(previousManifest)
+	if !ok {
+		return "", false
+	}
+	rel, err := filepath.Rel(sessionRoot, trimmed)
+	if err != nil {
+		return "", false
+	}
+	normalized, err := normalizeArchiveRelativePath(filepath.ToSlash(rel))
+	if err != nil {
+		return "", false
+	}
+	return normalized, true
+}
+
+func previousManifestSessionRoot(previousManifest *manifest.Manifest) (string, bool) {
+	if previousManifest == nil {
+		return "", false
+	}
+	runRoot := filepath.Clean(strings.TrimSpace(previousManifest.LocalWorkDir))
+	runID := strings.TrimSpace(previousManifest.RunID)
+	if runRoot == "" || runID == "" {
+		return "", false
+	}
+	if filepath.Base(runRoot) != runID {
+		return "", false
+	}
+	runsDir := filepath.Dir(runRoot)
+	if filepath.Base(runsDir) != config.PathRunsDirSegment {
+		return "", false
+	}
+	return filepath.Dir(runsDir), true
+}
+
+func previousManifestPromotedPaths(previousManifest *manifest.Manifest) []string {
+	if previousManifest == nil || len(previousManifest.Stages) == 0 {
+		return nil
+	}
+	sr := previousManifest.Stages["archive"]
+	if sr == nil || sr.Metadata == nil {
+		return nil
+	}
+	raw, ok := sr.Metadata["promoted_paths"]
+	if !ok {
+		return nil
+	}
+	values, ok := raw.([]any)
+	if !ok {
+		return nil
+	}
+	out := make([]string, 0, len(values))
+	for _, value := range values {
+		asString, ok := value.(string)
+		if !ok {
+			continue
+		}
+		normalized, err := normalizeArchiveRelativePath(asString)
+		if err != nil {
+			continue
+		}
+		out = append(out, normalized)
+	}
+	return dedupeOrderedStrings(out)
+}
+
+func dedupeOrderedStrings(values []string) []string {
+	if len(values) == 0 {
+		return nil
+	}
+	seen := map[string]struct{}{}
+	out := make([]string, 0, len(values))
+	for _, value := range values {
+		trimmed := strings.TrimSpace(value)
+		if trimmed == "" {
+			continue
+		}
+		if _, ok := seen[trimmed]; ok {
+			continue
+		}
+		seen[trimmed] = struct{}{}
+		out = append(out, trimmed)
+	}
+	return out
+}
+
+func downloadObjectToTempStage(
+	ctx context.Context,
+	store interface {
+		Download(context.Context, string, string) error
+	},
+	key, pattern string,
+) (string, error) {
+	tmp, err := os.CreateTemp("", pattern)
+	if err != nil {
+		return "", fmt.Errorf("create temp file: %w", err)
+	}
+	path := tmp.Name()
+	if err := tmp.Close(); err != nil {
+		_ = os.Remove(path)
+		return "", fmt.Errorf("close temp file: %w", err)
+	}
+	if err := store.Download(ctx, key, path); err != nil {
+		_ = os.Remove(path)
+		return "", err
+	}
+	return path, nil
+}

internal/stage/prepare_previous_test.go

@@ -0,0 +1,415 @@
+package stage
+
+import (
+	"context"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
+	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
+)
+
+func TestHydratePreviousSessionArtifactsDownloadsManifestAndRequiredArtifact(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+	seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: true,
+		includeArtifactObject:   true,
+		artifactBody:            "# previous recap\n",
+	})
+
+	result, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err != nil {
+		t.Fatalf("hydratePreviousSessionArtifacts() error = %v", err)
+	}
+	if result == nil {
+		t.Fatal("result is nil")
+	}
+	if len(result.Inputs) != 2 {
+		t.Fatalf("inputs len = %d, want 2", len(result.Inputs))
+	}
+	if !containsString(result.Hydrated, "session_recap") {
+		t.Fatalf("hydrated = %#v, want session_recap", result.Hydrated)
+	}
+	if len(result.SkippedMissing) != 0 {
+		t.Fatalf("skipped missing = %#v, want none", result.SkippedMissing)
+	}
+
+	if _, err := os.Stat(sessionPaths.PreviousManifestPath); err != nil {
+		t.Fatalf("previous manifest missing: %v", err)
+	}
+	recapPath := artifacts.SessionPreviousArtifactPath(sessionPaths, "artifacts/session_recap.md")
+	if _, err := os.Stat(recapPath); err != nil {
+		t.Fatalf("previous artifact missing: %v", err)
+	}
+
+	manifestInput := findInputByKind(result.Inputs, preparePreviousInputKindManifest)
+	if manifestInput == nil {
+		t.Fatalf("missing input kind %q", preparePreviousInputKindManifest)
+	}
+	if manifestInput.Source != preparePreviousInputSource {
+		t.Fatalf("manifest input source = %q, want %q", manifestInput.Source, preparePreviousInputSource)
+	}
+
+	artifactInput := findInputByKind(result.Inputs, preparePreviousInputKindArtifact)
+	if artifactInput == nil {
+		t.Fatalf("missing input kind %q", preparePreviousInputKindArtifact)
+	}
+	if artifactInput.Source != preparePreviousInputSource {
+		t.Fatalf("artifact input source = %q, want %q", artifactInput.Source, preparePreviousInputSource)
+	}
+	if artifactInput.Path != recapPath {
+		t.Fatalf("artifact input path = %q, want %q", artifactInput.Path, recapPath)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsSkipsMissingOptionalArtifact(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: false},
+	}
+	seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: true,
+		includeManifestObject:   true,
+		includeArtifactObject:   false,
+	})
+
+	result, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err != nil {
+		t.Fatalf("hydratePreviousSessionArtifacts() error = %v", err)
+	}
+	if result == nil {
+		t.Fatal("result is nil")
+	}
+	if !containsString(result.SkippedMissing, "session_recap") {
+		t.Fatalf("skipped missing = %#v, want session_recap", result.SkippedMissing)
+	}
+	if len(result.Hydrated) != 0 {
+		t.Fatalf("hydrated = %#v, want none", result.Hydrated)
+	}
+	manifestInput := findInputByKind(result.Inputs, preparePreviousInputKindManifest)
+	if manifestInput == nil {
+		t.Fatalf("missing input kind %q", preparePreviousInputKindManifest)
+	}
+	if findInputByKind(result.Inputs, preparePreviousInputKindArtifact) != nil {
+		t.Fatalf("unexpected %q input for missing optional artifact", preparePreviousInputKindArtifact)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsFailsMissingRequiredArtifact(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+	seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: true,
+		includeArtifactObject:   false,
+	})
+
+	_, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err == nil || !strings.Contains(err.Error(), "required previous-session artifact") {
+		t.Fatalf("error = %v, want required artifact failure", err)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsFailsRequiredWhenPreviousSessionIDUnset(t *testing.T) {
+	env, sessionPaths, _ := previousHydrationFixture(t)
+	env.Config.Session.PreviousSessionID = ""
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+
+	_, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err == nil || !strings.Contains(err.Error(), "previous_session_id is required") {
+		t.Fatalf("error = %v, want previous_session_id required failure", err)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsOptionalWithNoPreviousSessionID(t *testing.T) {
+	env, sessionPaths, _ := previousHydrationFixture(t)
+	env.Config.Session.PreviousSessionID = ""
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: false},
+	}
+
+	result, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err != nil {
+		t.Fatalf("hydratePreviousSessionArtifacts() error = %v", err)
+	}
+	if result == nil {
+		t.Fatal("result is nil")
+	}
+	if len(result.Inputs) != 0 {
+		t.Fatalf("inputs len = %d, want 0", len(result.Inputs))
+	}
+	if !containsString(result.SkippedMissing, "session_recap") {
+		t.Fatalf("skipped missing = %#v, want session_recap", result.SkippedMissing)
+	}
+	if _, err := os.Stat(sessionPaths.PreviousManifestPath); !os.IsNotExist(err) {
+		t.Fatalf("previous manifest should not be created, stat err = %v", err)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsRespectsCurrentCommitMarker(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+	seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: false,
+		includeArtifactObject:   true,
+		artifactBody:            "# previous recap\n",
+	})
+
+	_, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err == nil || !strings.Contains(err.Error(), "remote current run pointer missing") {
+		t.Fatalf("error = %v, want current run pointer missing failure", err)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsDoesNotUseLocalPreviousWorkspaceState(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+	seed := seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: true,
+		includeManifestObject:   true,
+		includeArtifactObject:   false,
+	})
+	// Write a local previous-session workspace file that should be ignored.
+	writeFile(t, filepath.Join(seed.PreviousSessionRoot, "artifacts", "session_recap.md"), "# local stale recap\n")
+
+	_, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err == nil || !strings.Contains(err.Error(), "object missing from archive") {
+		t.Fatalf("error = %v, want remote-object-missing failure", err)
+	}
+}
+
+func TestHydratePreviousSessionArtifactsUsesExplicitStorageKeys(t *testing.T) {
+	env, sessionPaths, fake := previousHydrationFixture(t)
+	requirements := []artifacts.PreviousArtifactRequirement{
+		{Name: "session_recap", Required: true},
+	}
+	seed := seedPreviousCurrentState(t, env, fake, previousStateSeedOptions{
+		includeRunPointerObject: true,
+		includeArtifactObject:   true,
+		artifactBody:            "# previous recap\n",
+	})
+
+	capture := &preparePreviousCaptureStore{delegate: fake}
+	env.ObjectStore = capture
+
+	_, err := hydratePreviousSessionArtifacts(context.Background(), env, sessionPaths, requirements)
+	if err != nil {
+		t.Fatalf("hydratePreviousSessionArtifacts() error = %v", err)
+	}
+
+	if !containsString(capture.existsKeys, seed.RunPointerKey) {
+		t.Fatalf("exists keys = %#v, want %q", capture.existsKeys, seed.RunPointerKey)
+	}
+	if !containsString(capture.existsKeys, seed.ManifestKey) {
+		t.Fatalf("exists keys = %#v, want %q", capture.existsKeys, seed.ManifestKey)
+	}
+	if !containsString(capture.existsKeys, seed.ArtifactKey) {
+		t.Fatalf("exists keys = %#v, want %q", capture.existsKeys, seed.ArtifactKey)
+	}
+	if !containsString(capture.downloadKeys, seed.RunPointerKey) {
+		t.Fatalf("download keys = %#v, want %q", capture.downloadKeys, seed.RunPointerKey)
+	}
+	if !containsString(capture.downloadKeys, seed.ManifestKey) {
+		t.Fatalf("download keys = %#v, want %q", capture.downloadKeys, seed.ManifestKey)
+	}
+	if !containsString(capture.downloadKeys, seed.ArtifactKey) {
+		t.Fatalf("download keys = %#v, want %q", capture.downloadKeys, seed.ArtifactKey)
+	}
+}
+
+type previousStateSeedResult struct {
+	PreviousSessionPrefix string
+	PreviousSessionRoot   string
+	ManifestKey           string
+	RunPointerKey         string
+	ArtifactKey           string
+}
+
+type previousStateSeedOptions struct {
+	includeRunPointerObject bool
+	includeManifestObject   bool
+	includeArtifactObject   bool
+	artifactBody            string
+}
+
+func seedPreviousCurrentState(
+	t *testing.T,
+	env *Env,
+	fake *storage.FakeBackend,
+	options previousStateSeedOptions,
+) previousStateSeedResult {
+	t.Helper()
+
+	if !options.includeRunPointerObject && !options.includeManifestObject && !options.includeArtifactObject {
+		// Keep default behavior deterministic when caller omits explicit flags.
+		options.includeRunPointerObject = true
+		options.includeManifestObject = true
+	}
+	if options.includeManifestObject == false && options.includeArtifactObject {
+		options.includeManifestObject = true
+	}
+
+	previousSessionID := strings.TrimSpace(env.Config.Session.PreviousSessionID)
+	campaign := strings.TrimSpace(env.Config.Session.Campaign)
+	rootPrefix := strings.TrimSpace(env.Config.Pipeline.Storage.S3.RootPrefix)
+	previousSessionPrefix := artifacts.S3SessionPrefix(rootPrefix, campaign, previousSessionID)
+	manifestKey, runPointerKey := artifacts.ResolveArchiveCurrentStateKeys(previousSessionPrefix)
+
+	previousRunID := "20260510T010203Z-a1b2c3d4"
+	previousSessionRoot := filepath.Join(t.TempDir(), "work", campaign, previousSessionID)
+	artifactLocalPath := filepath.Join(previousSessionRoot, "artifacts", "session_recap.md")
+	previousManifest := buildPreviousManifestForSeed(
+		t,
+		previousSessionID,
+		campaign,
+		previousRunID,
+		filepath.Join(previousSessionRoot, "runs", previousRunID),
+		artifactLocalPath,
+	)
+
+	if options.includeRunPointerObject || (!options.includeRunPointerObject && !options.includeManifestObject && !options.includeArtifactObject) {
+		fake.SeedObject(storage.FakeObject{
+			Key:  runPointerKey,
+			Data: []byte(previousRunID + "\n"),
+		})
+	}
+	if options.includeManifestObject || options.includeArtifactObject {
+		fake.SeedObject(storage.FakeObject{
+			Key:  manifestKey,
+			Data: previousManifest,
+		})
+	}
+
+	artifactKey := artifacts.S3PromotedArtifactKey(previousSessionPrefix, "artifacts/session_recap.md")
+	if options.includeArtifactObject {
+		body := options.artifactBody
+		if body == "" {
+			body = "# previous recap\n"
+		}
+		fake.SeedObject(storage.FakeObject{
+			Key:  artifactKey,
+			Data: []byte(body),
+		})
+	}
+
+	return previousStateSeedResult{
+		PreviousSessionPrefix: previousSessionPrefix,
+		PreviousSessionRoot:   previousSessionRoot,
+		ManifestKey:           manifestKey,
+		RunPointerKey:         runPointerKey,
+		ArtifactKey:           artifactKey,
+	}
+}
+
+func previousHydrationFixture(t *testing.T) (*Env, artifacts.SessionPaths, *storage.FakeBackend) {
+	t.Helper()
+	env, m := setupPrepareEnv(t)
+	env.Config.Session.Campaign = "forsaken"
+	env.Config.Session.PreviousSessionID = "2026-05-10"
+	env.Config.Pipeline.Storage.S3 = &config.StorageS3Config{
+		Bucket:     "my-dnd-archive",
+		RootPrefix: "dnd",
+	}
+	env.Config.Pipeline.Scriptorium = &config.ScriptoriumConfig{
+		Artifacts: map[string]config.ScriptoriumArtifactConfig{
+			"session_recap": {
+				Enabled:    true,
+				OutputPath: "artifacts/session_recap.md",
+			},
+		},
+	}
+	fake := &storage.FakeBackend{}
+	env.ObjectStore = fake
+
+	paths, err := ensureLayoutForEnv(env, m.SessionID)
+	if err != nil {
+		t.Fatalf("ensureLayoutForEnv() error = %v", err)
+	}
+	return env, paths, fake
+}
+
+func buildPreviousManifestForSeed(
+	t *testing.T,
+	sessionID, campaign, runID, runRoot, artifactPath string,
+) []byte {
+	t.Helper()
+	now := time.Date(2026, 5, 19, 22, 0, 0, 0, time.UTC)
+	m := manifest.New(sessionID, now)
+	m.Campaign = campaign
+	m.RunID = runID
+	m.LocalWorkDir = runRoot
+	m.MarkStageSucceeded("analyze", now, []manifest.ArtifactRecord{
+		{
+			Kind:      "scriptorium_artifact",
+			SourceID:  artifacts.ConfiguredArtifactSourceID("session_recap"),
+			LocalPath: artifactPath,
+		},
+	})
+	m.MarkStageSucceeded("archive", now, nil)
+	m.Stages["archive"].Metadata = map[string]any{
+		"promoted_paths": []string{"artifacts/session_recap.md"},
+	}
+	data, err := json.MarshalIndent(m, "", "  ")
+	if err != nil {
+		t.Fatalf("marshal manifest: %v", err)
+	}
+	return append(data, '\n')
+}
+
+type preparePreviousCaptureStore struct {
+	delegate     storage.ObjectStore
+	existsKeys   []string
+	downloadKeys []string
+}
+
+func (s *preparePreviousCaptureStore) List(ctx context.Context, prefix string) ([]storage.ObjectInfo, error) {
+	return s.delegate.List(ctx, prefix)
+}
+
+func (s *preparePreviousCaptureStore) Download(ctx context.Context, key, localPath string) error {
+	s.downloadKeys = append(s.downloadKeys, key)
+	return s.delegate.Download(ctx, key, localPath)
+}
+
+func (s *preparePreviousCaptureStore) Upload(ctx context.Context, localPath, key string, opts storage.UploadOptions) (storage.ObjectInfo, error) {
+	return s.delegate.Upload(ctx, localPath, key, opts)
+}
+
+func (s *preparePreviousCaptureStore) Exists(ctx context.Context, key string) (bool, error) {
+	s.existsKeys = append(s.existsKeys, key)
+	return s.delegate.Exists(ctx, key)
+}
+
+func findInputByKind(inputs []manifest.InputRecord, kind string) *manifest.InputRecord {
+	for i := range inputs {
+		if inputs[i].Kind == kind {
+			return &inputs[i]
+		}
+	}
+	return nil
+}
+
+func containsString(values []string, target string) bool {
+	for _, value := range values {
+		if value == target {
+			return true
+		}
+	}
+	return false
+}