Add previous-session workspace path helpers and layout support

internal/artifacts/paths.go

@@ -23,6 +23,9 @@ type SessionPaths struct {
 	LogsDir               string
 	CurrentDir            string
 	RunsDir               string
+	PreviousDir           string
+	PreviousManifestPath  string
+	PreviousArtifactsDir  string
 	ManifestPath          string
 	LockPath              string
 }
@@ -42,6 +45,29 @@ func SessionRunsDirForCampaign(rootDir, campaign, sessionID string) string {
 	return filepath.Join(SessionWorkDirForCampaign(rootDir, campaign, sessionID), config.PathRunsDirSegment)
 }
 
+// SessionPreviousDirForCampaign returns the canonical previous-session state directory.
+func SessionPreviousDirForCampaign(rootDir, campaign, sessionID string) string {
+	return filepath.Join(SessionWorkDirForCampaign(rootDir, campaign, sessionID), config.PathPreviousDirSegment)
+}
+
+// SessionPreviousManifestPathForCampaign returns the canonical previous-session manifest cache path.
+func SessionPreviousManifestPathForCampaign(rootDir, campaign, sessionID string) string {
+	return filepath.Join(SessionPreviousDirForCampaign(rootDir, campaign, sessionID), config.PathManifestFile)
+}
+
+// SessionPreviousArtifactsDirForCampaign returns the canonical previous-session artifact cache directory.
+func SessionPreviousArtifactsDirForCampaign(rootDir, campaign, sessionID string) string {
+	return filepath.Join(SessionPreviousDirForCampaign(rootDir, campaign, sessionID), config.PathArtifactsDirSegment)
+}
+
+// SessionPreviousArtifactPathForCampaign returns a path under previous/artifacts for one artifact.
+func SessionPreviousArtifactPathForCampaign(rootDir, campaign, sessionID, artifactRelativePath string) string {
+	return filepath.Join(
+		SessionPreviousArtifactsDirForCampaign(rootDir, campaign, sessionID),
+		filepath.FromSlash(artifactRelativePath),
+	)
+}
+
 // SessionRunRootForCampaign returns the canonical run root under runs/{run_id}.
 func SessionRunRootForCampaign(rootDir, campaign, sessionID, runID string) string {
 	return filepath.Join(SessionRunsDirForCampaign(rootDir, campaign, sessionID), runID)
@@ -62,6 +88,26 @@ func SessionSpoolAudioDir(spoolRoot, campaign, sessionID, runID string) string {
 	return filepath.Join(spoolRoot, campaign, sessionID, runID, config.PathAudioDirSegment)
 }
 
+// SessionPreviousDir returns the previous-session state directory for already-resolved session paths.
+func SessionPreviousDir(paths SessionPaths) string {
+	return paths.PreviousDir
+}
+
+// SessionPreviousManifestPath returns the previous-session manifest path for already-resolved session paths.
+func SessionPreviousManifestPath(paths SessionPaths) string {
+	return paths.PreviousManifestPath
+}
+
+// SessionPreviousArtifactsDir returns the previous-session artifact directory for already-resolved session paths.
+func SessionPreviousArtifactsDir(paths SessionPaths) string {
+	return paths.PreviousArtifactsDir
+}
+
+// SessionPreviousArtifactPath returns a path under previous/artifacts for already-resolved session paths.
+func SessionPreviousArtifactPath(paths SessionPaths, artifactRelativePath string) string {
+	return filepath.Join(paths.PreviousArtifactsDir, filepath.FromSlash(artifactRelativePath))
+}
+
 func buildSessionPaths(workspaceRoot, campaign, sessionID string) SessionPaths {
 	root := SessionWorkDirForCampaign(workspaceRoot, campaign, sessionID)
 	return buildSessionPathsFromRoot(workspaceRoot, campaign, sessionID, root)
@@ -84,6 +130,9 @@ func buildSessionPathsFromRoot(workspaceRoot, campaign, sessionID, root string)
 		LogsDir:               filepath.Join(root, config.PathLogsDirSegment),
 		CurrentDir:            filepath.Join(root, config.PathCurrentDirSegment),
 		RunsDir:               filepath.Join(root, config.PathRunsDirSegment),
+		PreviousDir:           filepath.Join(root, config.PathPreviousDirSegment),
+		PreviousManifestPath:  filepath.Join(root, config.PathPreviousDirSegment, config.PathManifestFile),
+		PreviousArtifactsDir:  filepath.Join(root, config.PathPreviousDirSegment, config.PathArtifactsDirSegment),
 		ManifestPath:          filepath.Join(root, config.PathManifestFile),
 		LockPath:              filepath.Join(root, config.PathLockFile),
 	}