feat: cancel_job over REST (Database::cancel_job + remote impl + pyo3 + python)

Exposes the existing server-side CANCEL JOB (CoordinatorCatalog::cancel_job)
as a REST-backed SDK method: Database trait default NotSupported,
RemoteDatabase POSTs /v1/job/{id}/cancel, pyo3 binding, sync+async python
wrappers. Best-effort: a missing job returns false, not an error. Mock-HTTP
unit test in test_derived_compute_routes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

rust/lancedb/src/connection.rs

@@ -547,6 +547,12 @@ impl Connection {
         self.internal.list_jobs().await
     }
 
+    /// Cancel an inflight server-side job by id. Returns true if a
+    /// matching inflight job was flagged for cancellation.
+    pub async fn cancel_job(&self, job_id: &str) -> Result<bool> {
+        self.internal.cancel_job(job_id).await
+    }
+
     /// Rename a table in the database.
     ///
     /// This is only supported in LanceDB Cloud.

rust/lancedb/src/database.rs

@@ -418,6 +418,12 @@ pub trait Database:
     async fn list_jobs(&self) -> Result<Vec<JobInfo>> {
         not_supported("list_jobs")
     }
+    /// Cancel an inflight server-side job by id. Returns true if a
+    /// matching inflight job was found and flagged for cancellation,
+    /// false if none was inflight (best-effort, like SQL `CANCEL JOB`).
+    async fn cancel_job(&self, _job_id: &str) -> Result<bool> {
+        not_supported("cancel_job")
+    }
 
     /// Open a table in the database
     async fn open_table(&self, request: OpenTableRequest) -> Result<Arc<dyn BaseTable>>;

rust/lancedb/src/remote/db.rs

@@ -139,6 +139,11 @@ struct RemoteListJobsResponse {
     jobs: Vec<RemoteJobEntry>,
 }
 
+#[derive(serde::Deserialize)]
+struct RemoteCancelJobResponse {
+    cancelled: bool,
+}
+
 // Request structure for the remote clone table API
 #[derive(serde::Serialize)]
 struct RemoteCloneTableRequest {
@@ -890,6 +895,14 @@ impl<S: HttpSend> Database for RemoteDatabase<S> {
             .collect())
     }
 
+    async fn cancel_job(&self, job_id: &str) -> Result<bool> {
+        let req = self.client.post(&format!("/v1/job/{}/cancel", job_id));
+        let (request_id, rsp) = self.client.send(req).await?;
+        let rsp = self.client.check_response(&request_id, rsp).await?;
+        let body: RemoteCancelJobResponse = rsp.json().await.err_to_http(request_id)?;
+        Ok(body.cancelled)
+    }
+
     async fn open_table(&self, request: OpenTableRequest) -> Result<Arc<dyn BaseTable>> {
         let identifier = build_table_identifier(
             &request.name,
@@ -1977,6 +1990,27 @@ mod tests {
         assert_eq!(jobs.len(), 1);
         assert_eq!(jobs[0].state, "running");
         assert_eq!(jobs[0].units_total, Some(2));
+
+        // cancel_job
+        let conn = Connection::new_with_handler(|request| {
+            assert_eq!(request.method(), &reqwest::Method::POST);
+            assert_eq!(request.url().path(), "/v1/job/j-3/cancel");
+            http::Response::builder()
+                .status(200)
+                .body(r#"{"cancelled":true}"#)
+                .unwrap()
+        });
+        assert!(conn.cancel_job("j-3").await.unwrap());
+
+        // cancel_job: no such inflight job -> false, not an error
+        let conn = Connection::new_with_handler(|request| {
+            assert_eq!(request.url().path(), "/v1/job/gone/cancel");
+            http::Response::builder()
+                .status(200)
+                .body(r#"{"cancelled":false}"#)
+                .unwrap()
+        });
+        assert!(!conn.cancel_job("gone").await.unwrap());
     }
 
     #[tokio::test]