diff --git a/crates/workspace-server/src/store.rs b/crates/workspace-server/src/store.rs
index 00243bd9..db1e06cd 100644
--- a/crates/workspace-server/src/store.rs
+++ b/crates/workspace-server/src/store.rs
@@ -5237,8 +5237,9 @@ fn workspace_resource_reference_diagnostics(conn: &Connection) -> Result<Vec<Str
                    AND ticket.ticket_id = link.ticket_id) LIMIT 100",
         ),
         // Historical assignment/operation rows intentionally survive Ticket or Worker
-        // retention deletion. A parent missing from every Workspace is therefore a retained
-        // soft reference; a matching id that exists only in another Workspace is corruption.
+        // retention deletion. A parent id missing from every Workspace is therefore a retained
+        // soft reference; a matching Ticket id in another Workspace, or a live Worker id whose
+        // Workspace/Runtime placement does not match the snapshot, is corruption.
         (
             "ticket_worker_assignments.ticket_id",
             "SELECT assignment.workspace_id || '/' || assignment.assignment_id || ' -> ' || assignment.ticket_id \
@@ -5255,9 +5256,10 @@ fn workspace_resource_reference_diagnostics(conn: &Connection) -> Result<Vec<Str
              FROM ticket_worker_assignments AS assignment \
              WHERE NOT EXISTS (SELECT 1 FROM worker_registry AS worker \
                  WHERE worker.workspace_id = assignment.workspace_id \
+                   AND worker.runtime_id = assignment.runtime_id \
                    AND worker.worker_id = assignment.worker_id) \
-               AND EXISTS (SELECT 1 FROM worker_registry AS foreign_worker \
-                 WHERE foreign_worker.worker_id = assignment.worker_id) LIMIT 100",
+               AND EXISTS (SELECT 1 FROM worker_registry AS live_worker \
+                 WHERE live_worker.worker_id = assignment.worker_id) LIMIT 100",
         ),
         (
             "ticket_current_worker_assignments.assignment_id",
@@ -8501,6 +8503,12 @@ INSERT INTO ticket_worker_assignments (
     'workspace-b', 'ticket-b', 'assignment-cross-worker', 'runtime-a',
     '00000000-0000-7000-8000-000000000001', 'tester', '2026-01-01'
 );
+INSERT INTO ticket_worker_assignments (
+    workspace_id, ticket_id, assignment_id, runtime_id, worker_id, assigned_by, assigned_at
+) VALUES (
+    'workspace-b', 'ticket-b', 'assignment-runtime-mismatch', 'runtime-wrong',
+    '00000000-0000-7000-8000-000000000002', 'tester', '2026-01-01'
+);
 INSERT INTO ticket_worker_assignments (
     workspace_id, ticket_id, assignment_id, runtime_id, worker_id, assigned_by, assigned_at
 ) VALUES (
@@ -8543,6 +8551,7 @@ INSERT INTO ticket_worker_assignment_events (
             "{error}"
         );
         assert!(error.contains("assignment-cross-worker"), "{error}");
+        assert!(error.contains("assignment-runtime-mismatch"), "{error}");
         assert!(
             error.contains("ticket_worker_assignment_events.assignment_id"),
             "{error}"
@@ -8597,6 +8606,14 @@ INSERT INTO ticket_worker_assignment_events (
             [],
         );
         assert!(cross_worker_assignment.is_err());
+        let runtime_mismatch_assignment = conn.execute(
+            "INSERT INTO ticket_worker_assignments \
+             (workspace_id, ticket_id, assignment_id, runtime_id, worker_id, assigned_by, assigned_at) \
+             VALUES ('workspace-b', 'ticket-b', 'assignment-runtime-mismatch', 'runtime-wrong', \
+             '00000000-0000-7000-8000-000000000002', 'tester', '2026-01-01')",
+            [],
+        );
+        assert!(runtime_mismatch_assignment.is_err());
         conn.execute(
             "INSERT INTO ticket_worker_assignments \
              (workspace_id, ticket_id, assignment_id, runtime_id, worker_id, assigned_by, assigned_at) \
diff --git a/docs/development/workspace-schema-migrations.md b/docs/development/workspace-schema-migrations.md
index db7c8ff1..27eabfc1 100644
--- a/docs/development/workspace-schema-migrations.md
+++ b/docs/development/workspace-schema-migrations.md
@@ -21,7 +21,7 @@ Start exactly one instance of the new Server binary against the database. Startu
 
 - rebuilds Ticket, Objective, assignment, Artifact, and human-key tables with Workspace-scoped composite identity;
 - adds composite foreign keys for repository, Ticket, Objective, Worker, relation-target, and current-assignment references;
-- validates new historical assignment/event references with SQLite triggers while allowing those audit rows to survive later Ticket or Worker retention deletion; startup treats a parent missing from every Workspace as retained history but still rejects an id that resolves only in another Workspace; reservation operation ids remain intentionally unconstrained until their resources exist;
+- validates new historical assignment/event references with SQLite triggers while allowing those audit rows to survive later Ticket or Worker retention deletion; startup treats a Ticket or Worker ID missing from every Workspace as retained history, but rejects a Ticket ID in another Workspace and rejects a live Worker ID whose Workspace/Runtime placement does not match the assignment snapshot; reservation operation ids remain intentionally unconstrained until their resources exist;
 - checks the rebuilt schema with `PRAGMA foreign_key_check` before recording the schema version; and
 - restores `PRAGMA foreign_keys = ON` whether the transaction commits or rolls back.