FabledScribe/tests/test_mcp_list_family.py

"""Cross-family contracts for the `list_*` MCP tools (#2278, shape 4).

Per-tool tests cover what each list tool does. Nothing covered what the FAMILY
owes its callers, which is where the missing-sibling shape hides: a capability
added to one member and not its neighbour changes no return value, so no
behavioural test can see it. Source inspection can.

WHAT THIS DELIBERATELY DOES NOT ASSERT. The 19 `list_*` tools are genuinely
heterogeneous — 8 take `project_id`, 6 take `limit`, and six take no arguments
at all (`list_projects`, `list_trash`, `list_rulebooks`, `list_design_systems`,
`list_repo_bindings`, `list_starter_role_groups`). Requiring a common parameter
across them would be inventing a convention the API does not have, which the
DRY process's over-DRY guard (§5) warns against by name: a wrong abstraction is
worse than the duplication. So this file asserts ONE contract, the one that is
a real promise rather than a shape coincidence.

THE CONTRACT: a `limit` without an `offset` is a truncation with no
continuation. The caller is told there are 250 results and handed 50, with no
way to ask for the rest. Both tools that had this were capped over a service
that already accepted an offset — `snippets_svc.list_snippets(offset=0)` was
simply not exposed, and `list_processes` passed a hardcoded `offset=0` into
`query_knowledge`. The capability existed one layer down in both cases; only
the door was missing.

As in `test_mcp_auth`, the CANDIDATES are derived and the DECISION is explicit.
Deriving the exemption too would make the contract follow a naming convention,
so any future `list_*` could opt itself out by accident.
"""
import ast
import pathlib

TOOLS_DIR = pathlib.Path(__file__).resolve().parents[1] / "src" / "scribe" / "mcp" / "tools"

# `limit` here caps a RANKED top-N, not a page into a corpus, so there is no
# "rest" to ask for — the 51st most-used tag is not what the caller wanted and
# an offset into that ordering answers no question. Anything added here needs a
# reason of that kind, not "it isn't paged yet".
_DELIBERATELY_UNPAGED = {
    "list_tags",        # most-used tags by count, over a bounded vocabulary
}


def _list_tools() -> dict[str, set[str]]:
    """{tool name: parameter names} for every `list_*` in the tools package."""
    out: dict[str, set[str]] = {}
    for path in sorted(TOOLS_DIR.glob("*.py")):
        if path.name == "__init__.py":
            continue
        for node in ast.parse(path.read_text()).body:
            if (
                isinstance(node, (ast.AsyncFunctionDef, ast.FunctionDef))
                and node.name.startswith("list_")
            ):
                out[node.name] = {
                    a.arg for a in node.args.args
                } | {a.arg for a in node.args.kwonlyargs}
    return out


def test_the_tools_package_is_where_we_think_it_is():
    """If this fails the sweep below is silently checking nothing."""
    tools = _list_tools()
    assert len(tools) >= 15, f"found only {len(tools)} list tools — did the package move?"


def test_every_capped_list_tool_can_be_paged():
    """A `limit` promises a cap; without an `offset` it also imposes a ceiling."""
    tools = _list_tools()
    capped = {name for name, args in tools.items() if "limit" in args}
    assert capped, "no list tool takes a limit — the sweep is not finding signatures"

    unpageable = sorted(
        name for name in capped
        if "offset" not in tools[name] and name not in _DELIBERATELY_UNPAGED
    )
    assert not unpageable, (
        f"these list tools cap their results with no way to page past the cap: "
        f"{unpageable}. Each hands the caller a `total` it cannot reach. Add an "
        f"`offset` (check the service first — it usually already takes one), or "
        f"add the tool to _DELIBERATELY_UNPAGED with a reason saying why there "
        f"is no 'rest' to ask for."
    )


def test_the_unpaged_exemptions_still_exist():
    """A stale exemption is an exemption for nothing, and it hides the next
    tool that inherits the name. Same reverse check `test_mcp_auth` runs on
    its allow-lists."""
    tools = _list_tools()
    missing = sorted(_DELIBERATELY_UNPAGED - set(tools))
    assert not missing, (
        f"_DELIBERATELY_UNPAGED names tools that no longer exist: {missing}. "
        f"Renamed or deleted — drop them from the set."
    )
    still_capped = sorted(
        name for name in _DELIBERATELY_UNPAGED
        if name in tools and "limit" not in tools[name]
    )
    assert not still_capped, (
        f"these are exempted from paging but no longer take a `limit` at all, "
        f"so the exemption is moot: {still_capped}."
    )


def test_offset_never_appears_without_limit():
    """The inverse, and it is a real bug rather than a style point: an offset
    with no cap pages through an unbounded result set, so page 2 of an
    ever-growing list silently returns everything after the skip."""
    tools = _list_tools()
    bad = sorted(
        name for name, args in tools.items()
        if "offset" in args and "limit" not in args
    )
    assert not bad, f"these take an offset but no limit: {bad}"