fix(session): list_namespaces mirrors list_tables resolution

[YuangGao]

Changes Made

Session.list_namespaces ignored attached catalogs and raised when no current catalog was set. It now mirrors Session::list_tables (#7126):

• Rule 3: <catalog>.<rest> patterns dispatch exclusively to that attached catalog
• Otherwise: namespaces from the current catalog, qualified with the session alias so results round-trip through set_namespace / list_tables / read_table
• No current catalog returns [] instead of raising ValueError

Adds Session::list_namespaces in Rust + PySession shim and switches the Python wrapper to delegate.

Related Issues

Closes #7134

[greptile-apps]

Greptile Summary

This PR fixes Session.list_namespaces to mirror the catalog-resolution logic already implemented in Session.list_tables (#7126), adding a Rust-level Session::list_namespaces and a PySession shim so the Python wrapper can simply delegate.

• Rule 3 dispatch: a <catalog>.<rest> pattern is routed exclusively to that attached catalog, results qualified with the catalog alias so they round-trip through set_namespace / list_tables / read_table.
• Current-catalog fallback: with no catalog-qualified pattern the current catalog is queried; if no current catalog is set an empty list is returned instead of raising ValueError.
• MemoryCatalog pattern support: the hard error on any non-None pattern is replaced with proper SQL LIKE filtering via the existing match_pattern helper.

Confidence Score: 5/5

Safe to merge — the change is a well-scoped addition with no modifications to existing write paths or table resolution logic.

The new list_namespaces logic is a direct structural copy of the already-tested list_tables dispatch, the MemoryCatalog change replaces an unconditional error with correct filtering, and five integration tests cover all documented scenarios including the round-trip property.

No files require special attention.

Important Files Changed

Filename	Overview
src/daft-session/src/session.rs	Adds list_namespaces that mirrors list_tables Rule 3 dispatch and current-catalog fallback; logic is correct and consistent.
src/daft-catalog/src/impls/memory.rs	Replaces the hard error on any pattern with proper SQL LIKE filtering via match_pattern; logic is sound.
src/daft-session/src/python.rs	Thin PyO3 shim for list_namespaces — correct, follows the same pattern as list_tables.
daft/session.py	Python wrapper now delegates to the Rust list_namespaces instead of calling the catalog directly; removes the ValueError on missing current catalog.
daft/daft/init.pyi	Adds type stub for the new PySession.list_namespaces method.
tests/test_session.py	Adds five targeted tests covering the four dispatch scenarios plus the round-trip property with list_tables; good coverage.
tests/catalog/test_memory.py	Adds a test for the new MemoryCatalog pattern-filtering behavior; correct assertions.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Session.list_namespaces(pattern)"] --> B{pattern has a dot\nAND head is\nattached catalog?}
    B -- Yes --> C["get_catalog(head)\n.list_namespaces(rest)"]
    C --> D["qualify results\nwith catalog alias"]
    D --> E["return [cat.ns, ...]"]
    B -- No --> F{current catalog\nset?}
    F -- No --> G["return []"]
    F -- Yes --> H["get_catalog(alias)\n.list_namespaces(pattern)"]
    H --> I["qualify results\nwith alias"]
    I --> E

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flowchart TD
    A["Session.list_namespaces(pattern)"] --> B{pattern has a dot\nAND head is\nattached catalog?}
    B -- Yes --> C["get_catalog(head)\n.list_namespaces(rest)"]
    C --> D["qualify results\nwith catalog alias"]
    D --> E["return [cat.ns, ...]"]
    B -- No --> F{current catalog\nset?}
    F -- No --> G["return []"]
    F -- Yes --> H["get_catalog(alias)\n.list_namespaces(pattern)"]
    H --> I["qualify results\nwith alias"]
    I --> E

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