merge: quote merge-key identifiers with dest dialect

Incremental merge interpolated merge-key columns raw, so a key with a
character illegal in a bare identifier (e.g. dcord#) produced
WHERE dcord# IN (...) and Postgres errored at "IN". build_merge_sql now
takes the dest driver and quotes each key via quote_identifier (clean
names stay bare, the rest wrap in the dialect's quotes).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pipekit/engine/merge.py

@@ -19,7 +19,13 @@ class MergeError(ValueError):
 
 
 def build_merge_sql(*, strategy: str, dest_table: str, staging_table: str,
-                    merge_key: str | None) -> str:
+                    merge_key: str | None, dest_drv=None) -> str:
+    # Quote merge-key identifiers with the dest dialect. Keys are user-entered
+    # and may hold characters illegal in a bare identifier (e.g. '#', spaces,
+    # mixed case) — PG's quote_identifier leaves clean names bare and wraps the
+    # rest in "…". Falls back to raw when no driver is supplied.
+    quote = dest_drv.quote_identifier if dest_drv else (lambda s: s)
+
     if strategy == "full":
         return f"TRUNCATE TABLE {dest_table};\nINSERT INTO {dest_table} SELECT * FROM {staging_table};"
 
@@ -29,7 +35,7 @@ def build_merge_sql(*, strategy: str, dest_table: str, staging_table: str,
     if strategy == "incremental":
         if not merge_key:
             raise MergeError("incremental merge requires merge_key")
-        keys = [k.strip() for k in merge_key.split(",") if k.strip()]
+        keys = [quote(k.strip()) for k in merge_key.split(",") if k.strip()]
         if not keys:
             raise MergeError(f"merge_key is empty after parsing: {merge_key!r}")
         if len(keys) == 1:

pipekit/engine/runner.py

@@ -93,6 +93,7 @@ def run_module(module_id: int, *, group_run_id: int | None = None,
             dest_table=module["dest_table"],
             staging_table=module["staging_table"],
             merge_key=module["merge_key"],
+            dest_drv=dest_drv,
         )
         repo.log_run_sql(run_id, merge_sql=merge_sql)