diff --git a/crates/domain/src/entities/mod.rs b/crates/domain/src/entities/mod.rs
index 2b794e3..2a7f1e3 100644
--- a/crates/domain/src/entities/mod.rs
+++ b/crates/domain/src/entities/mod.rs
@@ -45,3 +45,9 @@ pub use share_target::{ShareTarget, TargetType};
 pub use share_link::{LinkAccessLevel, ShareLink};
 pub use invite_code::InviteCode;
 pub use visibility_filter::VisibilityFilter;
+
+mod sidecar_record;
+mod sidecar_config;
+
+pub use sidecar_record::{SidecarRecord, SyncStatus};
+pub use sidecar_config::{ConflictPolicy, SidecarConfig, SyncMode};
diff --git a/crates/domain/src/entities/sidecar_config.rs b/crates/domain/src/entities/sidecar_config.rs
new file mode 100644
index 0000000..7ab71e7
--- /dev/null
+++ b/crates/domain/src/entities/sidecar_config.rs
@@ -0,0 +1,30 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub enum SyncMode {
+    Auto,
+    Scheduled,
+    Manual,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub enum ConflictPolicy {
+    DbWins,
+    FileWins,
+    RequireUserDecision,
+}
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct SidecarConfig {
+    pub export_base_path: String,
+    pub sync_mode: SyncMode,
+    pub conflict_resolution_policy: ConflictPolicy,
+}
+
+impl Default for SidecarConfig {
+    fn default() -> Self {
+        Self {
+            export_base_path: "/kphotos/sidecars".to_string(),
+            sync_mode: SyncMode::Auto,
+            conflict_resolution_policy: ConflictPolicy::DbWins,
+        }
+    }
+}
diff --git a/crates/domain/src/entities/sidecar_record.rs b/crates/domain/src/entities/sidecar_record.rs
new file mode 100644
index 0000000..ade3f8a
--- /dev/null
+++ b/crates/domain/src/entities/sidecar_record.rs
@@ -0,0 +1,57 @@
+use crate::value_objects::{Checksum, DateTimeStamp, SystemId};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+pub enum SyncStatus {
+    InSync,
+    PendingWrite,
+    PendingRead,
+    Conflict,
+    Error,
+}
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct SidecarRecord {
+    pub asset_id: SystemId,
+    pub sync_status: SyncStatus,
+    pub sidecar_storage_path: String,
+    pub last_synced_at: Option<DateTimeStamp>,
+    pub last_known_file_hash: Option<Checksum>,
+    pub error_message: Option<String>,
+}
+
+impl SidecarRecord {
+    pub fn new(asset_id: SystemId, path: impl Into<String>) -> Self {
+        Self {
+            asset_id,
+            sync_status: SyncStatus::PendingWrite,
+            sidecar_storage_path: path.into(),
+            last_synced_at: None,
+            last_known_file_hash: None,
+            error_message: None,
+        }
+    }
+
+    pub fn mark_synced(&mut self, file_hash: Checksum) {
+        self.sync_status = SyncStatus::InSync;
+        self.last_synced_at = Some(DateTimeStamp::now());
+        self.last_known_file_hash = Some(file_hash);
+        self.error_message = None;
+    }
+
+    pub fn mark_pending_write(&mut self) {
+        self.sync_status = SyncStatus::PendingWrite;
+    }
+
+    pub fn mark_pending_read(&mut self) {
+        self.sync_status = SyncStatus::PendingRead;
+    }
+
+    pub fn mark_conflict(&mut self) {
+        self.sync_status = SyncStatus::Conflict;
+    }
+
+    pub fn mark_error(&mut self, message: impl Into<String>) {
+        self.sync_status = SyncStatus::Error;
+        self.error_message = Some(message.into());
+    }
+}
diff --git a/crates/domain/src/ports/mod.rs b/crates/domain/src/ports/mod.rs
index 1719354..05375cb 100644
--- a/crates/domain/src/ports/mod.rs
+++ b/crates/domain/src/ports/mod.rs
@@ -45,3 +45,9 @@ mod visibility_filter_repo;
 
 pub use share_repo::ShareRepository;
 pub use visibility_filter_repo::VisibilityFilterRepository;
+
+mod sidecar_repo;
+mod sidecar_writer;
+
+pub use sidecar_repo::SidecarRepository;
+pub use sidecar_writer::SidecarWriterPort;
diff --git a/crates/domain/src/ports/sidecar_repo.rs b/crates/domain/src/ports/sidecar_repo.rs
new file mode 100644
index 0000000..36ef14c
--- /dev/null
+++ b/crates/domain/src/ports/sidecar_repo.rs
@@ -0,0 +1,10 @@
+use async_trait::async_trait;
+use crate::{entities::{SidecarRecord, SyncStatus}, errors::DomainError, value_objects::SystemId};
+
+#[async_trait]
+pub trait SidecarRepository: Send + Sync {
+    async fn find_by_asset(&self, asset_id: &SystemId) -> Result<Option<SidecarRecord>, DomainError>;
+    async fn find_by_status(&self, status: SyncStatus) -> Result<Vec<SidecarRecord>, DomainError>;
+    async fn save(&self, record: &SidecarRecord) -> Result<(), DomainError>;
+    async fn delete(&self, asset_id: &SystemId) -> Result<(), DomainError>;
+}
diff --git a/crates/domain/src/ports/sidecar_writer.rs b/crates/domain/src/ports/sidecar_writer.rs
new file mode 100644
index 0000000..aaf56ec
--- /dev/null
+++ b/crates/domain/src/ports/sidecar_writer.rs
@@ -0,0 +1,9 @@
+use async_trait::async_trait;
+use crate::{errors::DomainError, value_objects::StructuredData};
+
+#[async_trait]
+pub trait SidecarWriterPort: Send + Sync {
+    fn format_name(&self) -> &str;
+    async fn write_sidecar(&self, data: &StructuredData, path: &str) -> Result<(), DomainError>;
+    async fn read_sidecar(&self, path: &str) -> Result<StructuredData, DomainError>;
+}
diff --git a/crates/domain/tests/entities/mod.rs b/crates/domain/tests/entities/mod.rs
index 3e2d312..a37b7a1 100644
--- a/crates/domain/tests/entities/mod.rs
+++ b/crates/domain/tests/entities/mod.rs
@@ -15,3 +15,4 @@ mod album;
 mod tag;
 mod share_scope;
 mod share_link;
+mod sidecar_record;
diff --git a/crates/domain/tests/entities/sidecar_record.rs b/crates/domain/tests/entities/sidecar_record.rs
new file mode 100644
index 0000000..95b8fd2
--- /dev/null
+++ b/crates/domain/tests/entities/sidecar_record.rs
@@ -0,0 +1,31 @@
+use domain::entities::{SidecarRecord, SyncStatus};
+use domain::value_objects::{Checksum, SystemId};
+
+#[test]
+fn new_is_pending_write() {
+    let record = SidecarRecord::new(SystemId::new(), "/path/to/sidecar.xmp");
+    assert_eq!(record.sync_status, SyncStatus::PendingWrite);
+    assert!(record.last_synced_at.is_none());
+    assert!(record.last_known_file_hash.is_none());
+}
+
+#[test]
+fn sync_lifecycle() {
+    let mut record = SidecarRecord::new(SystemId::new(), "/path/to/sidecar.xmp");
+
+    let hash = Checksum::new("a".repeat(64)).unwrap();
+    record.mark_synced(hash);
+    assert_eq!(record.sync_status, SyncStatus::InSync);
+    assert!(record.last_synced_at.is_some());
+    assert!(record.last_known_file_hash.is_some());
+
+    record.mark_pending_read();
+    assert_eq!(record.sync_status, SyncStatus::PendingRead);
+
+    record.mark_conflict();
+    assert_eq!(record.sync_status, SyncStatus::Conflict);
+
+    record.mark_error("disk full");
+    assert_eq!(record.sync_status, SyncStatus::Error);
+    assert_eq!(record.error_message.as_deref(), Some("disk full"));
+}