diff --git a/core/db.py b/core/db.py
index dcc40e9..6ce0b33 100644
--- a/core/db.py
+++ b/core/db.py
@@ -737,6 +737,35 @@ def _migrate(conn: sqlite3.Connection):
             )
             conn.commit()
 
+    # Add UNIQUE(from_project, to_project, type) to project_links (KIN-INFRA-013).
+    # SQLite does not support ALTER TABLE ADD CONSTRAINT — table recreation required.
+    if "project_links" in existing_tables:
+        pl_sql_row = conn.execute(
+            "SELECT sql FROM sqlite_master WHERE type='table' AND name='project_links'"
+        ).fetchone()
+        pl_has_unique = pl_sql_row and "UNIQUE" in (pl_sql_row[0] or "").upper()
+        if not pl_has_unique:
+            conn.executescript("""
+                PRAGMA foreign_keys=OFF;
+                CREATE TABLE project_links_new (
+                    id INTEGER PRIMARY KEY AUTOINCREMENT,
+                    from_project TEXT NOT NULL REFERENCES projects(id),
+                    to_project TEXT NOT NULL REFERENCES projects(id),
+                    type TEXT NOT NULL,
+                    description TEXT,
+                    created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
+                    UNIQUE(from_project, to_project, type)
+                );
+                INSERT OR IGNORE INTO project_links_new
+                    SELECT id, from_project, to_project, type, description, created_at
+                    FROM project_links;
+                DROP TABLE project_links;
+                ALTER TABLE project_links_new RENAME TO project_links;
+                CREATE INDEX IF NOT EXISTS idx_project_links_to ON project_links(to_project);
+                CREATE INDEX IF NOT EXISTS idx_project_links_from ON project_links(from_project);
+                PRAGMA foreign_keys=ON;
+            """)
+
 
 def _seed_default_hooks(conn: sqlite3.Connection):
     """Seed default hooks for the kin project (idempotent).
diff --git a/tests/test_api_pipeline_logs.py b/tests/test_api_pipeline_logs.py
index 20284e0..f9c1324 100644
--- a/tests/test_api_pipeline_logs.py
+++ b/tests/test_api_pipeline_logs.py
@@ -58,13 +58,14 @@ def test_get_pipeline_logs_empty_returns_empty_list(pipeline_client):
 
 
 # ─────────────────────────────────────────────────────────────
-# Тест: несуществующий pipeline → 404 (Convention #420)
+# Тест: несуществующий pipeline → 200 [] (KIN-OBS-023)
 # ─────────────────────────────────────────────────────────────
 
-def test_get_pipeline_logs_nonexistent_pipeline_returns_404(client):
-    """GET /api/pipelines/99999/logs возвращает 404 для несуществующего pipeline."""
+def test_get_pipeline_logs_nonexistent_pipeline_returns_empty(client):
+    """KIN-OBS-023: GET /api/pipelines/99999/logs → 200 [] (log collections return empty, not 404)."""
     r = client.get("/api/pipelines/99999/logs")
-    assert r.status_code == 404
+    assert r.status_code == 200
+    assert r.json() == []
 
 
 # ─────────────────────────────────────────────────────────────