diff --git a/Cargo.lock b/Cargo.lock
index 5832534..5738665 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1145,6 +1145,23 @@ dependencies = [
  "libloading 0.8.9",
 ]
 
+[[package]]
+name = "doctate-client-core"
+version = "0.1.0"
+dependencies = [
+ "doctate-common",
+ "reqwest",
+ "serde",
+ "serde_json",
+ "tempfile",
+ "thiserror 1.0.69",
+ "time",
+ "tokio",
+ "tracing",
+ "uuid",
+ "wiremock",
+]
+
 [[package]]
 name = "doctate-common"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index 6c69e94..75726b5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,5 +1,5 @@
 [workspace]
-members = ["server", "doctate-common", "client-desktop"]
+members = ["server", "doctate-common", "doctate-client-core", "client-desktop"]
 resolver = "3"
 
 [workspace.package]
diff --git a/doctate-client-core/Cargo.toml b/doctate-client-core/Cargo.toml
new file mode 100644
index 0000000..8875c19
--- /dev/null
+++ b/doctate-client-core/Cargo.toml
@@ -0,0 +1,21 @@
+[package]
+name = "doctate-client-core"
+version.workspace = true
+edition.workspace = true
+description = "Shared client logic for the doctate medical dictation system: case store, oneliner poller, snapshot cache"
+
+[dependencies]
+doctate-common = { path = "../doctate-common" }
+tokio = { workspace = true }
+reqwest = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
+uuid = { workspace = true }
+time = { workspace = true }
+tracing = { workspace = true }
+thiserror = "1"
+
+[dev-dependencies]
+tempfile = "3"
+tokio = { workspace = true, features = ["test-util"] }
+wiremock = "0.6"
diff --git a/doctate-client-core/src/case_store.rs b/doctate-client-core/src/case_store.rs
new file mode 100644
index 0000000..cdbf862
--- /dev/null
+++ b/doctate-client-core/src/case_store.rs
@@ -0,0 +1,502 @@
+//! Per-case marker store for native clients.
+//!
+//! Each known case (either created locally by this client or seen in a
+//! server snapshot) has one JSON file: `{dir}/{case_id}.json`. The store
+//! keeps an in-memory copy and broadcasts a sorted snapshot on every
+//! write via [`tokio::sync::watch`].
+//!
+//! The merge-with-server-snapshot logic only **adds or updates** markers.
+//! It never deletes: `/api/oneliners` is a sliding-window view, not a
+//! full case inventory, so "missing from snapshot" is ambiguous (deleted
+//! vs. fell out of the window). Cleanup is a separate, later concern.
+
+use std::collections::HashMap;
+use std::path::{Path, PathBuf};
+use std::sync::Arc;
+
+use doctate_common::oneliners::OnelinersResponse;
+use serde::{Deserialize, Serialize};
+use thiserror::Error;
+use time::format_description::well_known::Rfc3339;
+use time::OffsetDateTime;
+use tokio::sync::{watch, Mutex};
+use tracing::{debug, warn};
+use uuid::Uuid;
+
+/// On-disk representation of a single case known to this client.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+pub struct CaseMarker {
+    pub case_id: Uuid,
+    /// RFC3339 UTC; set once at creation or on first server-snapshot merge.
+    pub created_at: String,
+    /// RFC3339 UTC; bumped on every new recording + on server-snapshot
+    /// updates. Drives the UI sort order (newest activity first).
+    pub last_activity_at: String,
+    /// `true` once this case has been seen in any `/api/oneliners`
+    /// response. Reserved for future delete-propagation logic; today only
+    /// useful for diagnostics.
+    pub synced_to_server: bool,
+    /// `None` while transcription / oneliner generation is pending; set
+    /// from the server snapshot when available.
+    pub oneliner: Option<String>,
+}
+
+#[derive(Debug, Error)]
+pub enum CaseStoreError {
+    #[error("I/O error at {path}: {source}")]
+    Io {
+        path: PathBuf,
+        #[source]
+        source: std::io::Error,
+    },
+    #[error("serialize marker: {0}")]
+    Serialize(#[from] serde_json::Error),
+    #[error("format timestamp: {0}")]
+    Format(#[from] time::error::Format),
+}
+
+type Snapshot = Arc<Vec<CaseMarker>>;
+
+/// Shared case store. Cheap to `clone()`; clones share the same state.
+#[derive(Clone)]
+pub struct CaseStore {
+    dir: PathBuf,
+    state: Arc<Mutex<HashMap<Uuid, CaseMarker>>>,
+    tx: watch::Sender<Snapshot>,
+}
+
+impl CaseStore {
+    /// Open or create the store at `dir`. Reads every `*.json` file in
+    /// the directory as an initial marker. Returns the store plus a
+    /// receiver that yields sorted snapshots (newest `last_activity_at`
+    /// first) on every mutation.
+    pub async fn open(dir: PathBuf) -> Result<(Self, watch::Receiver<Snapshot>), CaseStoreError> {
+        tokio::fs::create_dir_all(&dir)
+            .await
+            .map_err(|e| CaseStoreError::Io {
+                path: dir.clone(),
+                source: e,
+            })?;
+
+        let initial = read_all_markers(&dir).await?;
+        let map: HashMap<Uuid, CaseMarker> =
+            initial.into_iter().map(|m| (m.case_id, m)).collect();
+        let snapshot = sorted_snapshot(&map);
+        let (tx, rx) = watch::channel(snapshot);
+
+        let store = Self {
+            dir,
+            state: Arc::new(Mutex::new(map)),
+            tx,
+        };
+        Ok((store, rx))
+    }
+
+    /// Append a new case the client itself just started (no server
+    /// knowledge yet). Writes the marker atomically and broadcasts the
+    /// new snapshot. If a marker with the same `case_id` already exists,
+    /// it is overwritten — callers must check before if that matters.
+    pub async fn create_local(
+        &self,
+        case_id: Uuid,
+        at: OffsetDateTime,
+    ) -> Result<CaseMarker, CaseStoreError> {
+        let ts = format_utc(at)?;
+        let marker = CaseMarker {
+            case_id,
+            created_at: ts.clone(),
+            last_activity_at: ts,
+            synced_to_server: false,
+            oneliner: None,
+        };
+        let mut state = self.state.lock().await;
+        write_marker_file(&self.dir, &marker).await?;
+        state.insert(case_id, marker.clone());
+        self.broadcast(&state);
+        Ok(marker)
+    }
+
+    /// Record new activity on an existing case (e.g. a follow-up
+    /// recording). Creates the marker if missing — callers may invoke
+    /// this after an upload without caring whether `create_local` ran
+    /// first. `synced_to_server` is preserved.
+    pub async fn mark_activity(
+        &self,
+        case_id: Uuid,
+        at: OffsetDateTime,
+    ) -> Result<(), CaseStoreError> {
+        let ts = format_utc(at)?;
+        let mut state = self.state.lock().await;
+        let marker = state.entry(case_id).or_insert_with(|| CaseMarker {
+            case_id,
+            created_at: ts.clone(),
+            last_activity_at: ts.clone(),
+            synced_to_server: false,
+            oneliner: None,
+        });
+        marker.last_activity_at = ts;
+        write_marker_file(&self.dir, marker).await?;
+        self.broadcast(&state);
+        Ok(())
+    }
+
+    /// Apply a server `/api/oneliners` response. For every entry in the
+    /// snapshot: insert (with `synced_to_server = true`) or update the
+    /// local marker (oneliner + last_activity_at from server timestamps,
+    /// taking the newer of local vs. server). Never deletes.
+    pub async fn merge_server_snapshot(
+        &self,
+        snapshot: &OnelinersResponse,
+    ) -> Result<(), CaseStoreError> {
+        let mut state = self.state.lock().await;
+        for entry in &snapshot.oneliners {
+            let Ok(case_id) = Uuid::parse_str(&entry.case_id) else {
+                warn!(case_id = %entry.case_id, "server snapshot entry with invalid case_id, skipped");
+                continue;
+            };
+            let server_activity = entry
+                .updated_at
+                .clone()
+                .unwrap_or_else(|| entry.created_at.clone());
+
+            let updated_marker = match state.get(&case_id) {
+                Some(existing) => {
+                    let mut m = existing.clone();
+                    m.synced_to_server = true;
+                    m.oneliner = entry.oneliner.clone();
+                    // Keep whichever `last_activity_at` is newer — the
+                    // client may have recorded an addendum the server
+                    // hasn't processed yet.
+                    if server_activity > m.last_activity_at {
+                        m.last_activity_at = server_activity;
+                    }
+                    m
+                }
+                None => CaseMarker {
+                    case_id,
+                    created_at: entry.created_at.clone(),
+                    last_activity_at: server_activity,
+                    synced_to_server: true,
+                    oneliner: entry.oneliner.clone(),
+                },
+            };
+            write_marker_file(&self.dir, &updated_marker).await?;
+            state.insert(case_id, updated_marker);
+        }
+        self.broadcast(&state);
+        Ok(())
+    }
+
+    /// Remove every marker from memory and disk. Used on config change
+    /// (new API key = potentially different user).
+    pub async fn clear_all(&self) -> Result<(), CaseStoreError> {
+        let mut state = self.state.lock().await;
+        let mut entries =
+            tokio::fs::read_dir(&self.dir)
+                .await
+                .map_err(|e| CaseStoreError::Io {
+                    path: self.dir.clone(),
+                    source: e,
+                })?;
+        while let Ok(Some(entry)) = entries.next_entry().await {
+            let path = entry.path();
+            if path.extension().and_then(|s| s.to_str()) != Some("json") {
+                continue;
+            }
+            if let Err(e) = tokio::fs::remove_file(&path).await {
+                warn!(path = %path.display(), error = %e, "failed to remove marker during clear");
+            }
+        }
+        state.clear();
+        self.broadcast(&state);
+        Ok(())
+    }
+
+    /// Current in-memory list, for tests and inspection.
+    pub async fn list(&self) -> Vec<CaseMarker> {
+        let state = self.state.lock().await;
+        sorted_vec(&state)
+    }
+
+    fn broadcast(&self, state: &HashMap<Uuid, CaseMarker>) {
+        let snapshot = sorted_snapshot(state);
+        // receiver-count=0 is fine (nobody listening); ignore.
+        let _ = self.tx.send(snapshot);
+    }
+}
+
+fn format_utc(at: OffsetDateTime) -> Result<String, time::error::Format> {
+    at.to_offset(time::UtcOffset::UTC).format(&Rfc3339)
+}
+
+fn sorted_snapshot(state: &HashMap<Uuid, CaseMarker>) -> Snapshot {
+    Arc::new(sorted_vec(state))
+}
+
+fn sorted_vec(state: &HashMap<Uuid, CaseMarker>) -> Vec<CaseMarker> {
+    let mut v: Vec<CaseMarker> = state.values().cloned().collect();
+    v.sort_by(|a, b| b.last_activity_at.cmp(&a.last_activity_at));
+    v
+}
+
+async fn read_all_markers(dir: &Path) -> Result<Vec<CaseMarker>, CaseStoreError> {
+    let mut out = Vec::new();
+    let mut entries = tokio::fs::read_dir(dir).await.map_err(|e| CaseStoreError::Io {
+        path: dir.to_owned(),
+        source: e,
+    })?;
+    while let Ok(Some(entry)) = entries.next_entry().await {
+        let path = entry.path();
+        if path.extension().and_then(|s| s.to_str()) != Some("json") {
+            continue;
+        }
+        match read_marker_file(&path).await {
+            Ok(m) => out.push(m),
+            Err(e) => {
+                // A single unreadable file should not poison the store;
+                // log and skip so recovery of the rest proceeds.
+                warn!(path = %path.display(), error = %e, "skipping unreadable marker");
+            }
+        }
+    }
+    Ok(out)
+}
+
+async fn read_marker_file(path: &Path) -> Result<CaseMarker, CaseStoreError> {
+    let bytes = tokio::fs::read(path).await.map_err(|e| CaseStoreError::Io {
+        path: path.to_owned(),
+        source: e,
+    })?;
+    Ok(serde_json::from_slice(&bytes)?)
+}
+
+/// Write a marker atomically: temp-file + rename. The rename on the same
+/// filesystem is atomic on POSIX and NTFS, so readers never see a
+/// partially-written file.
+async fn write_marker_file(dir: &Path, marker: &CaseMarker) -> Result<(), CaseStoreError> {
+    let bytes = serde_json::to_vec_pretty(marker)?;
+    let final_path = dir.join(format!("{}.json", marker.case_id));
+    let tmp_path = dir.join(format!("{}.json.tmp", marker.case_id));
+    tokio::fs::write(&tmp_path, &bytes)
+        .await
+        .map_err(|e| CaseStoreError::Io {
+            path: tmp_path.clone(),
+            source: e,
+        })?;
+    tokio::fs::rename(&tmp_path, &final_path)
+        .await
+        .map_err(|e| CaseStoreError::Io {
+            path: final_path.clone(),
+            source: e,
+        })?;
+    debug!(path = %final_path.display(), "marker written");
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use doctate_common::oneliners::OnelinerEntry;
+    use tempfile::TempDir;
+
+    fn t(s: &str) -> OffsetDateTime {
+        OffsetDateTime::parse(s, &Rfc3339).unwrap()
+    }
+
+    fn server_entry(case_id: Uuid, oneliner: Option<&str>, created: &str) -> OnelinerEntry {
+        OnelinerEntry {
+            case_id: case_id.to_string(),
+            oneliner: oneliner.map(str::to_owned),
+            created_at: created.to_owned(),
+            updated_at: Some(created.to_owned()),
+        }
+    }
+
+    fn server_snapshot(entries: Vec<OnelinerEntry>) -> OnelinersResponse {
+        OnelinersResponse {
+            as_of: "2026-04-18T10:00:00Z".into(),
+            window_hours: 72,
+            oneliners: entries,
+        }
+    }
+
+    #[tokio::test]
+    async fn create_local_persists_and_reloads() {
+        let tmp = TempDir::new().unwrap();
+        let (store, mut rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        assert!(rx.borrow().is_empty());
+
+        let id = Uuid::new_v4();
+        let marker = store.create_local(id, t("2026-04-18T10:32:00Z")).await.unwrap();
+        assert_eq!(marker.case_id, id);
+        assert!(!marker.synced_to_server);
+        assert!(marker.oneliner.is_none());
+
+        rx.changed().await.unwrap();
+        let snap = rx.borrow().clone();
+        assert_eq!(snap.len(), 1);
+        assert_eq!(snap[0].case_id, id);
+
+        // Reopen: state must survive.
+        drop(store);
+        let (store2, _rx2) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        assert_eq!(store2.list().await.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn mark_activity_updates_timestamp() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.create_local(id, t("2026-04-18T10:00:00Z")).await.unwrap();
+        store.mark_activity(id, t("2026-04-18T10:45:00Z")).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list.len(), 1);
+        assert_eq!(list[0].last_activity_at, "2026-04-18T10:45:00Z");
+        // `created_at` must not change.
+        assert_eq!(list[0].created_at, "2026-04-18T10:00:00Z");
+    }
+
+    #[tokio::test]
+    async fn mark_activity_creates_if_missing() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.mark_activity(id, t("2026-04-18T10:00:00Z")).await.unwrap();
+        assert_eq!(store.list().await.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn merge_adds_unknown_server_case() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        let snap = server_snapshot(vec![server_entry(
+            id,
+            Some("Kniegelenk re."),
+            "2026-04-18T09:30:00Z",
+        )]);
+        store.merge_server_snapshot(&snap).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list.len(), 1);
+        assert_eq!(list[0].case_id, id);
+        assert_eq!(list[0].oneliner.as_deref(), Some("Kniegelenk re."));
+        assert!(list[0].synced_to_server);
+    }
+
+    #[tokio::test]
+    async fn merge_updates_existing_local_marker() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.create_local(id, t("2026-04-18T10:00:00Z")).await.unwrap();
+
+        let snap = server_snapshot(vec![server_entry(
+            id,
+            Some("Hypertonie"),
+            "2026-04-18T10:00:00Z",
+        )]);
+        store.merge_server_snapshot(&snap).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list.len(), 1);
+        assert!(list[0].synced_to_server);
+        assert_eq!(list[0].oneliner.as_deref(), Some("Hypertonie"));
+    }
+
+    #[tokio::test]
+    async fn merge_keeps_local_when_missing_from_server() {
+        // User recorded locally, upload not yet through. Server snapshot
+        // is empty — marker must survive.
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.create_local(id, t("2026-04-18T10:00:00Z")).await.unwrap();
+
+        let snap = server_snapshot(vec![]);
+        store.merge_server_snapshot(&snap).await.unwrap();
+
+        assert_eq!(store.list().await.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn merge_keeps_synced_marker_when_missing_from_server() {
+        // Case was synced earlier, now out of the server's time window.
+        // Must not be deleted.
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.create_local(id, t("2026-04-18T10:00:00Z")).await.unwrap();
+        let synced_snap = server_snapshot(vec![server_entry(
+            id,
+            Some("old"),
+            "2026-04-18T10:00:00Z",
+        )]);
+        store.merge_server_snapshot(&synced_snap).await.unwrap();
+
+        // Next poll: server window moved, case fell out.
+        store.merge_server_snapshot(&server_snapshot(vec![])).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list.len(), 1);
+        assert!(list[0].synced_to_server);
+        assert_eq!(list[0].oneliner.as_deref(), Some("old"));
+    }
+
+    #[tokio::test]
+    async fn merge_prefers_newer_last_activity() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let id = Uuid::new_v4();
+        store.create_local(id, t("2026-04-18T09:00:00Z")).await.unwrap();
+        store.mark_activity(id, t("2026-04-18T11:00:00Z")).await.unwrap();
+
+        // Server says last activity was 10:00 (stale) — local 11:00 must win.
+        let snap = server_snapshot(vec![server_entry(
+            id,
+            Some("x"),
+            "2026-04-18T10:00:00Z",
+        )]);
+        store.merge_server_snapshot(&snap).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list[0].last_activity_at, "2026-04-18T11:00:00Z");
+    }
+
+    #[tokio::test]
+    async fn clear_all_removes_everything() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        store.create_local(Uuid::new_v4(), t("2026-04-18T10:00:00Z")).await.unwrap();
+        store.create_local(Uuid::new_v4(), t("2026-04-18T11:00:00Z")).await.unwrap();
+        assert_eq!(store.list().await.len(), 2);
+
+        store.clear_all().await.unwrap();
+        assert!(store.list().await.is_empty());
+        // Marker files on disk are gone.
+        let mut count = 0;
+        let mut entries = tokio::fs::read_dir(tmp.path()).await.unwrap();
+        while let Ok(Some(e)) = entries.next_entry().await {
+            if e.path().extension().and_then(|s| s.to_str()) == Some("json") {
+                count += 1;
+            }
+        }
+        assert_eq!(count, 0);
+    }
+
+    #[tokio::test]
+    async fn sorted_newest_first() {
+        let tmp = TempDir::new().unwrap();
+        let (store, _rx) = CaseStore::open(tmp.path().to_owned()).await.unwrap();
+        let older = Uuid::new_v4();
+        let newer = Uuid::new_v4();
+        store.create_local(older, t("2026-04-18T08:00:00Z")).await.unwrap();
+        store.create_local(newer, t("2026-04-18T10:00:00Z")).await.unwrap();
+
+        let list = store.list().await;
+        assert_eq!(list[0].case_id, newer);
+        assert_eq!(list[1].case_id, older);
+    }
+}
diff --git a/doctate-client-core/src/lib.rs b/doctate-client-core/src/lib.rs
new file mode 100644
index 0000000..f808221
--- /dev/null
+++ b/doctate-client-core/src/lib.rs
@@ -0,0 +1,20 @@
+//! Shared client logic for the doctate dictation system.
+//!
+//! This crate is filesystem- and network-aware (unlike `doctate-common`,
+//! which is DTO-only), but path-agnostic: callers pass concrete paths so
+//! the same code works on Linux desktop, Windows desktop, Android, iOS.
+//!
+//! Modules:
+//! - [`case_store`]: per-case marker files, merge-with-server-snapshot logic
+//! - [`snapshot_cache`]: last successful `/api/oneliners` response, cached
+//!   on disk so the UI has data at cold start
+//! - [`oneliner_poller`]: background task that polls the server and feeds
+//!   the case store
+
+pub mod case_store;
+pub mod oneliner_poller;
+pub mod snapshot_cache;
+
+pub use case_store::{CaseMarker, CaseStore, CaseStoreError};
+pub use oneliner_poller::{OnelinerPoller, PollerConfig};
+pub use snapshot_cache::{CachedSnapshot, SnapshotCache};
diff --git a/doctate-client-core/src/oneliner_poller.rs b/doctate-client-core/src/oneliner_poller.rs
new file mode 100644
index 0000000..8af7d18
--- /dev/null
+++ b/doctate-client-core/src/oneliner_poller.rs
@@ -0,0 +1,26 @@
+//! Placeholder — full implementation follows in next step.
+
+pub struct PollerConfig {
+    pub server_url: String,
+    pub api_key: String,
+    pub poll_interval: std::time::Duration,
+    pub window_hours: u32,
+}
+
+pub struct OnelinerPoller {
+    _abort: tokio::task::AbortHandle,
+}
+
+impl OnelinerPoller {
+    /// To be implemented.
+    #[doc(hidden)]
+    pub fn from_handle(abort: tokio::task::AbortHandle) -> Self {
+        Self { _abort: abort }
+    }
+}
+
+impl Drop for OnelinerPoller {
+    fn drop(&mut self) {
+        self._abort.abort();
+    }
+}
diff --git a/doctate-client-core/src/snapshot_cache.rs b/doctate-client-core/src/snapshot_cache.rs
new file mode 100644
index 0000000..289868d
--- /dev/null
+++ b/doctate-client-core/src/snapshot_cache.rs
@@ -0,0 +1,24 @@
+//! Placeholder — full implementation follows in next step.
+
+use std::path::PathBuf;
+
+use doctate_common::oneliners::OnelinersResponse;
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct CachedSnapshot {
+    pub etag: String,
+    pub fetched_at: String,
+    pub response: OnelinersResponse,
+}
+
+pub struct SnapshotCache {
+    #[allow(dead_code)]
+    path: PathBuf,
+}
+
+impl SnapshotCache {
+    pub fn new(path: PathBuf) -> Self {
+        Self { path }
+    }
+}
diff --git a/doctate-common/src/lib.rs b/doctate-common/src/lib.rs
index 6d421d9..7884b82 100644
--- a/doctate-common/src/lib.rs
+++ b/doctate-common/src/lib.rs
@@ -1,5 +1,6 @@
 pub mod ack;
 pub mod constants;
+pub mod oneliners;
 pub mod timestamp;
 
 pub use ack::{AckResponse, AckStatus};
@@ -7,4 +8,5 @@ pub use constants::{
     API_KEY_HEADER, CONTENT_TYPE_AUDIO_MP4, FIELD_AUDIO, FIELD_CASE_ID, FIELD_RECORDED_AT,
     UPLOAD_PATH,
 };
+pub use oneliners::{OnelinerEntry, OnelinersResponse, ONELINERS_PATH};
 pub use timestamp::{filename_stem_to_recorded_at, now_rfc3339, recorded_at_to_filename_stem};
diff --git a/doctate-common/src/oneliners.rs b/doctate-common/src/oneliners.rs
new file mode 100644
index 0000000..83d2e55
--- /dev/null
+++ b/doctate-common/src/oneliners.rs
@@ -0,0 +1,32 @@
+//! Shared DTOs for the `/api/oneliners` endpoint.
+//!
+//! Server serializes [`OnelinersResponse`]; clients deserialize the same
+//! type. Keeping this in a client-agnostic crate avoids drift between
+//! server output and client parsing.
+
+use serde::{Deserialize, Serialize};
+
+/// HTTP path of the oneliners endpoint.
+pub const ONELINERS_PATH: &str = "/api/oneliners";
+
+/// Full response body of `GET /api/oneliners`.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OnelinersResponse {
+    /// RFC3339 UTC timestamp at which the server built this response.
+    pub as_of: String,
+    /// Effective window (after server-side clamp).
+    pub window_hours: u32,
+    /// Oneliners of cases whose earliest recording sits inside the window,
+    /// sorted newest-first by `created_at`.
+    pub oneliners: Vec<OnelinerEntry>,
+}
+
+/// One case summary. `oneliner` is `None` while the case is still
+/// transcribing / generating; `updated_at` is `None` for the same reason.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct OnelinerEntry {
+    pub case_id: String,
+    pub oneliner: Option<String>,
+    pub created_at: String,
+    pub updated_at: Option<String>,
+}
diff --git a/server/src/routes/oneliners.rs b/server/src/routes/oneliners.rs
index d911106..c187b52 100644
--- a/server/src/routes/oneliners.rs
+++ b/server/src/routes/oneliners.rs
@@ -18,7 +18,8 @@ use axum::extract::{Query, State};
 use axum::http::{header, HeaderMap, StatusCode};
 use axum::response::{IntoResponse, Response};
 use axum::Json;
-use serde::{Deserialize, Serialize};
+use doctate_common::oneliners::{OnelinerEntry, OnelinersResponse};
+use serde::Deserialize;
 use time::format_description::well_known::Rfc3339;
 use time::{Duration, OffsetDateTime};
 use tracing::warn;
@@ -35,21 +36,6 @@ pub struct OnelinersQuery {
     hours: Option<u32>,
 }
 
-#[derive(Serialize)]
-struct OnelinersResponse {
-    as_of: String,
-    window_hours: u32,
-    oneliners: Vec<OnelinerEntry>,
-}
-
-#[derive(Serialize)]
-struct OnelinerEntry {
-    case_id: String,
-    oneliner: Option<String>,
-    created_at: String,
-    updated_at: Option<String>,
-}
-
 pub async fn handle_oneliners(
     user: AuthenticatedUser,
     State(watermark): State<OnelinerWatermark>,