Name the remedy for a missing configured database and list the databases an unknown name could have meant

A configured or default database that does not exist raises
SourceUnavailableError with the way to create it and without its location.
An unknown --db-name lists the databases there are, configured or default.
The CHANGELOG records Store.db_path, SingleDatabaseSession(ref, config),
the empty lancedb.uri migration and the error-type change.

CHANGELOG.md

@@ -5,7 +5,8 @@
 ### Removed
 
 - `lancedb.uri`. Write `lancedb.databases: {NAME: <location>}`; a config carrying
-  `uri` fails to load with that message.
+  `uri` fails to load with that message. Configurations generated by
+  `init-config` through 0.81 carry `uri: ""` and must drop the key.
 - `HAIKU_RAG_DB`. Capabilities cover the databases the configuration places, or
   the `db_path` argument.
 - `DB_PATH` in the `app/` backend and `examples/custom_agent_agui.py`. Both load
@@ -33,6 +34,12 @@
 - `DatabaseRef(name, location, given)` replaces `DatabaseRef(name, uri, db_path)`;
   `DatabaseScope.at(path)` added; `locate_database` returns `Path | str`.
   `IngesterApp(config, scope)` takes a resolved scope in place of `db_path`.
+  `SingleDatabaseSession(ref, config)` replaces `SingleDatabaseSession(db_path,
+  config, source=)`. `Store.db_path` is `None` for a database behind a URI.
+- Opening a configured or default database that does not exist raises
+  `SourceUnavailableError` naming the database and the remedy (`haiku-rag init`
+  or `create=True`), where the default database raised `FileNotFoundError` with
+  its path. A database given as a path still raises `FileNotFoundError`.
 - `Store(location, config)`, `connect_lancedb(location, config)`,
   `gather_database_info(location, config)` and `run_doctor(config, location, ...)`
   take the database location, a path or a URI. `ConnectionMode.of(location)`

docs/configuration/storage.md

@@ -110,7 +110,7 @@ async with HaikuRAG(create=True) as client:
 
 The [default location](index.md#configuration-file-locations) is platform-specific (e.g., `~/Library/Application Support/haiku.rag/` on macOS).
 
-Opening a nonexistent local database given as a path raises `FileNotFoundError`, naming the path. This prevents accidental database creation from typos or misconfigured paths. A database placed by `lancedb.databases` raises `SourceUnavailableError` instead, naming the database and not its location.
+Opening a nonexistent local database given as a path raises `FileNotFoundError`, naming the path. This prevents accidental database creation from typos or misconfigured paths. A configured or default database raises `SourceUnavailableError` instead, naming the database and not its location.
 
 ## Remote Storage
 

docs/python.md

@@ -27,7 +27,7 @@ async with HaikuRAG("path/to/database.lancedb", read_only=True) as client:
 `async with` is the lifecycle. A caller that owns the client some other way releases it with `await client.aclose()`, which does the same work for every client shape. `client.close()` closes the connection to one database and nothing else, since draining the background vacuum and releasing the embedder and reranker are awaitable; it refuses a client covering several.
 
 !!! note
-    Databases must be explicitly created with `create=True` or via `haiku-rag init` before use. Opening a nonexistent local database given as a path raises `FileNotFoundError`, naming the path; one placed by `lancedb.databases` raises `SourceUnavailableError`, which names the database rather than its location. A path beside a configured `lancedb.databases` raises `AmbiguousDatabaseError`.
+    Databases must be explicitly created with `create=True` or via `haiku-rag init` before use. Opening a nonexistent local database given as a path raises `FileNotFoundError`, naming the path; a configured or default database raises `SourceUnavailableError`, which names the database rather than its location. A path beside a configured `lancedb.databases` raises `AmbiguousDatabaseError`.
 
 !!! note
     Read-only mode is useful for safely accessing databases without risk of modification. It blocks all write operations and downgrades an embedding provider/name mismatch to a warning instead of raising `ConfigMismatchError`.

haiku_rag_slim/haiku/rag/client/scope.py

@@ -126,7 +126,7 @@ class DatabaseScope:
         if database_name is not None:
             if database_name not in declared:
                 raise UnknownDatabaseError(
-                    f"unknown database {database_name!r}; lancedb.databases names "
+                    f"unknown database {database_name!r}; the databases are "
                     f"{', '.join(sorted(declared))}"
                 )
             return cls(

haiku_rag_slim/haiku/rag/client/session.py

@@ -113,13 +113,15 @@ class SingleDatabaseSession:
             # A path the caller gave may be named: the caller knows it already.
             if self.ref.given:
                 raise
-            failure = type(error).__name__
+            failure = (
+                "does not exist; create it with `haiku-rag init` or `create=True`"
+                if isinstance(error, FileNotFoundError)
+                else f"could not be opened: {type(error).__name__}"
+            )
         if failure is not None:
             # Raised outside the handler: the exception carries neither a cause
             # nor a location-bearing context.
-            raise SourceUnavailableError(
-                f"database {self.source!r} could not be opened: {failure}"
-            )
+            raise SourceUnavailableError(f"database {self.source!r} {failure}")
         self.document_repository = DocumentRepository(self.store)
         self.chunk_repository = ChunkRepository(self.store)
         self.document_item_repository = DocumentItemRepository(self.store)

tests/ingester/test_cli.py

@@ -557,12 +557,6 @@ class TestPlacingTheIngesterDatabase:
         with pytest.raises(typer.BadParameter, match="no name"):
             _scope_for(Path("/"))
 
-    def test_a_python_caller_cannot_pass_a_path(self):
-        from haiku.rag.ingester.app import IngesterApp
-
-        with pytest.raises(TypeError):
-            IngesterApp(config=AppConfig(), db_path="/db/other.lancedb")  # type: ignore[call-arg]  # ty: ignore[unknown-argument]
-
     def test_one_configured_database_is_accepted(self, tmp_path):
         """A one-entry mapping names which database to write."""
         config = AppConfig(

tests/multi_db/test_lifecycle.py

@@ -474,6 +474,25 @@ class TestFailureNaming:
         assert str(tmp_path) not in str(caught.value)
         assert caught.value.__cause__ is None
 
+    @pytest.mark.asyncio
+    async def test_a_missing_default_database_names_the_remedy(self, tmp_path):
+        """The location stays out of the message; the way to create the
+        database does not."""
+        from haiku.rag.config.models import AppConfig, StorageConfig
+
+        config = AppConfig(storage=StorageConfig(data_dir=tmp_path / "empty"))
+
+        with pytest.raises(SourceUnavailableError) as caught:
+            async with HaikuRAG(config=config):
+                pass
+
+        message = str(caught.value)
+        assert "database 'haiku.rag' does not exist" in message
+        assert "haiku-rag init" in message
+        assert "create=True" in message
+        assert str(tmp_path) not in message
+        assert caught.value.__cause__ is None
+
     @pytest.mark.asyncio
     async def test_a_database_given_as_a_path_keeps_its_error(self, tmp_path):
         """The caller gave the path, so the error may name it."""

tests/test_database_scope.py

@@ -54,11 +54,21 @@ class TestResolution:
         assert scope.names == ("beta",)
 
     def test_an_unknown_name_is_refused(self):
+        """The message lists the databases there are, configured or default."""
         config = _config(databases={"alpha": "/data/alpha.lancedb"})
 
-        with pytest.raises(UnknownDatabaseError, match="unknown database 'nope'"):
+        with pytest.raises(
+            UnknownDatabaseError,
+            match="unknown database 'nope'.*the databases are alpha",
+        ):
             DatabaseScope.resolve(config, database_name="nope")
 
+        with pytest.raises(
+            UnknownDatabaseError,
+            match="unknown database 'nope'.*the databases are haiku.rag",
+        ):
+            DatabaseScope.resolve(_config(), database_name="nope")
+
     def test_no_selector_covers_the_configured_set_in_order(self):
         config = _config(
             databases={"beta": "/data/b.lancedb", "alpha": "/data/a.lancedb"}