Resolve canonical previous-session artifact sources from prepared previous cache

internal/artifacts/artifact_resolver.go

@@ -18,6 +18,9 @@ const (
 	ArtifactTranscriptFull     = "narratio.transcript.full"
 	ArtifactTranscriptTrimmed  = "narratio.transcript.trimmed"
 	ArtifactBoundsSession      = "narratio.bounds.session"
+
+	ArtifactProvenancePreviousCacheManifestInput = "manifest.inputs.previous_cache"
+	ArtifactProvenancePreviousCacheFilesystem    = "current_session.previous_cache"
 )
 
 // ErrSessionArtifactNotFound is returned when no readable artifact exists for a known ID.
@@ -186,6 +189,9 @@ func ResolveSessionArtifact(paths SessionPaths, m *manifest.Manifest, source str
 // configured narratio.artifact.<name> sources through runtime catalog availability.
 func ResolveSessionArtifactWithCatalog(paths SessionPaths, m *manifest.Manifest, source string, catalog *ArtifactCatalog) (ResolvedSessionArtifact, error) {
 	normalized := strings.TrimSpace(source)
+	if IsPreviousSessionArtifactSource(normalized) {
+		return ResolvePreviousSessionArtifactWithCatalog(paths, m, normalized, catalog)
+	}
 	if !IsConfiguredArtifactSource(normalized) {
 		return ResolveSessionArtifact(paths, m, normalized)
 	}
@@ -211,6 +217,72 @@ func ResolveSessionArtifactWithCatalog(paths SessionPaths, m *manifest.Manifest,
 	}, nil
 }
 
+// ResolvePreviousSessionArtifactWithCatalog resolves one canonical previous-session source id
+// to the prepared current-session previous-cache path.
+func ResolvePreviousSessionArtifactWithCatalog(
+	paths SessionPaths,
+	m *manifest.Manifest,
+	source string,
+	catalog *ArtifactCatalog,
+) (ResolvedSessionArtifact, error) {
+	artifactName, ok := PreviousSessionArtifactName(source)
+	if !ok {
+		return ResolvedSessionArtifact{}, fmt.Errorf("unsupported previous-session artifact source %q", source)
+	}
+	if catalog == nil {
+		return ResolvedSessionArtifact{}, fmt.Errorf("previous-session artifact source %q requires runtime artifact catalog", source)
+	}
+
+	configuredSourceID := ConfiguredArtifactSourceID(artifactName)
+	entry, ok := catalog.Lookup(configuredSourceID)
+	if !ok {
+		return ResolvedSessionArtifact{}, fmt.Errorf("unsupported previous-session artifact source %q", source)
+	}
+	candidates := previousSessionCacheCandidatePaths(paths, entry.CanonicalRelPath)
+	if len(candidates) == 0 {
+		return ResolvedSessionArtifact{}, &SessionArtifactNotFoundError{ArtifactID: source}
+	}
+
+	manifestInputPaths := manifestInputPathSet(paths, m)
+	fallback := ""
+	for _, candidate := range candidates {
+		exists, isDir, statErr := pathExists(candidate)
+		if statErr != nil {
+			return ResolvedSessionArtifact{}, fmt.Errorf("stat %q: %w", candidate, statErr)
+		}
+		if !exists || isDir {
+			continue
+		}
+		if err := validateResolvedContent(candidate, contentText); err != nil {
+			return ResolvedSessionArtifact{}, fmt.Errorf("validate %q: %w", source, err)
+		}
+		if _, ok := manifestInputPaths[candidate]; ok {
+			return ResolvedSessionArtifact{
+				ID:            source,
+				Path:          candidate,
+				ProducerStage: "prepare",
+				OutputKind:    "previous_session_artifact",
+				Provenance:    ArtifactProvenancePreviousCacheManifestInput,
+			}, nil
+		}
+		if fallback == "" {
+			fallback = candidate
+		}
+	}
+
+	if fallback != "" {
+		return ResolvedSessionArtifact{
+			ID:            source,
+			Path:          fallback,
+			ProducerStage: "prepare",
+			OutputKind:    "previous_session_artifact",
+			Provenance:    ArtifactProvenancePreviousCacheFilesystem,
+		}, nil
+	}
+
+	return ResolvedSessionArtifact{}, &SessionArtifactNotFoundError{ArtifactID: source}
+}
+
 func manifestArtifactCandidates(paths SessionPaths, m *manifest.Manifest, spec artifactSpec) []ResolvedSessionArtifact {
 	if m == nil || len(m.Stages) == 0 || spec.ProducerStage == "" || spec.OutputKind == "" {
 		return nil
@@ -259,6 +331,50 @@ func dedupeResolvedArtifacts(values []ResolvedSessionArtifact) []ResolvedSession
 	return out
 }
 
+func previousSessionCacheCandidatePaths(paths SessionPaths, canonicalRelPath string) []string {
+	trimmed := strings.TrimSpace(canonicalRelPath)
+	if trimmed == "" {
+		return nil
+	}
+	normalized := filepath.ToSlash(filepath.Clean(filepath.FromSlash(trimmed)))
+	if normalized == "." || normalized == "" || normalized == ".." || strings.HasPrefix(normalized, "../") || strings.HasPrefix(normalized, "/") {
+		return nil
+	}
+
+	relCandidates := []string{normalized}
+	const artifactsPrefix = "artifacts/"
+	if strings.HasPrefix(normalized, artifactsPrefix) && len(normalized) > len(artifactsPrefix) {
+		relCandidates = append(relCandidates, strings.TrimPrefix(normalized, artifactsPrefix))
+	}
+
+	out := make([]string, 0, len(relCandidates))
+	seen := map[string]struct{}{}
+	for _, rel := range relCandidates {
+		abs := filepath.Clean(SessionPreviousArtifactPath(paths, rel))
+		if _, ok := seen[abs]; ok {
+			continue
+		}
+		seen[abs] = struct{}{}
+		out = append(out, abs)
+	}
+	return out
+}
+
+func manifestInputPathSet(paths SessionPaths, m *manifest.Manifest) map[string]struct{} {
+	if m == nil || len(m.Inputs) == 0 {
+		return nil
+	}
+	out := make(map[string]struct{}, len(m.Inputs))
+	for _, in := range m.Inputs {
+		resolved := filepath.Clean(ResolveSessionLocalPathForRead(paths, in.Path))
+		if strings.TrimSpace(resolved) == "" {
+			continue
+		}
+		out[resolved] = struct{}{}
+	}
+	return out
+}
+
 func pathExists(path string) (exists bool, isDir bool, err error) {
 	info, err := os.Stat(path)
 	if err == nil {