Name a remedy the command being used has

`haiku-ingester` reached the client's refusal, which names `sources=[name]`, a
Python argument no CLI user can pass. It refuses a configured set itself, with
`--db PATH` and the one-ingester-per-database layout.

`haiku-rag`'s own refusal now says where each option goes: `--db-name` is global
and precedes the command, `--db` follows it.

haiku_rag_slim/haiku/rag/cli.py

@@ -105,8 +105,8 @@ def resolve_scope(
     if scope.covers_multiple and not covers_set:
         raise AmbiguousDatabaseError(
             f"lancedb.databases names {', '.join(sorted(scope.names))}; this "
-            "command works on a single database: pass --db-name NAME, or "
-            "--db PATH."
+            "command works on a single database: pass --db-name NAME before "
+            "the command, or --db PATH after it"
         )
     return scope
 

haiku_rag_slim/haiku/rag/ingester/app.py

@@ -74,11 +74,19 @@ class IngesterApp:
 
     def __init__(self, *, config: AppConfig, db_path: Path | None = None):
         from haiku.rag.client.scope import DatabaseScope
+        from haiku.rag.store.exceptions import AmbiguousDatabaseError
 
         self._config = config
         # `--db` names the database directly, and nothing stands in for it: a
         # manufactured default would override a configured `lancedb.uri`.
         self._scope = DatabaseScope.resolve(config, database_path=db_path)
+        if self._scope.covers_multiple:
+            raise AmbiguousDatabaseError(
+                "haiku-ingester writes one database, and lancedb.databases "
+                f"names {', '.join(self._scope.names)}; select one with "
+                "--db PATH, or give each database its own ingester with a "
+                "configuration naming a single one"
+            )
         self._engine: AsyncEngine | None = None
         self._jobs: JobRepo | None = None
         self._sync: SyncStateRepo | None = None

tests/ingester/test_cli.py

@@ -525,6 +525,23 @@ class TestPlacingTheIngesterDatabase:
         assert scope.names == ("docs",)
         assert not scope.covers_multiple
 
+    def test_a_set_is_refused_with_a_remedy_this_command_has(self, tmp_path):
+        """The client would name `sources=[name]`, a Python argument no CLI user
+        can pass."""
+        from haiku.rag.store.exceptions import AmbiguousDatabaseError
+
+        config = AppConfig(
+            lancedb=LanceDBConfig(
+                databases={"a": str(tmp_path / "a"), "b": str(tmp_path / "b")}
+            )
+        )
+
+        with pytest.raises(AmbiguousDatabaseError) as raised:
+            self._app(config)
+
+        assert "--db PATH" in str(raised.value)
+        assert "sources=" not in str(raised.value)
+
     def test_several_configured_databases_exit_cleanly(self, tmp_path, monkeypatch):
         """No selector names one of a set, so the CLI reports it rather than
         printing a traceback."""

tests/test_cli.py

@@ -116,9 +116,14 @@ class TestOneDatabaseCommands:
     def test_a_configured_set_refuses_a_one_database_command(self, monkeypatch):
         self._install(monkeypatch, alpha="/db/a.lancedb", beta="/db/b.lancedb")
 
-        with pytest.raises(AmbiguousDatabaseError, match="alpha, beta"):
+        with pytest.raises(AmbiguousDatabaseError, match="alpha, beta") as raised:
             resolve_scope(None)
 
+        # `--db-name` is global and `--db` is per-command, so the remedy says
+        # where each one goes.
+        assert "--db-name NAME before the command" in str(raised.value)
+        assert "--db PATH after it" in str(raised.value)
+
     def test_the_refusal_names_the_databases_and_not_their_locations(self, monkeypatch):
         """A location in an error message travels into logs and terminals; the
         names exist so it does not have to."""