Parameterized scoring mismatch and subquery error

Start in postgres/src/score.rs, especially score_support(), combine_constant_queries(), and the caller around the cited lines. Reproduce both cases with the SQL in the issue, then trace parameter handling and scorer context propagation; done means parameterized and literal queries produce matching scores and the subquery aggregate no longer raises the context error.

Ran into a couple issues with using lead for running tests versus actual hosted tin.

Environment: Lead 1.0.3, commit bd95c7e, PostgreSQL 18.6.

Using parameters instead of identical literals changes relevance scores.

Reproduction:

CREATE TEMP TABLE lead_score_repro (
    id integer PRIMARY KEY,
    title text NOT NULL
);

INSERT INTO lead_score_repro VALUES
    (1, 'lorem ipsum'),
    (2, 'lorem ipsun');

CREATE INDEX ON lead_score_repro USING tin (title);
ANALYZE lead_score_repro;

PREPARE lead_ranked(text, text) AS
SELECT id, tin.score(ctid) AS score
FROM lead_score_repro
WHERE title ==> $1 AND title ==> $2
ORDER BY id;

EXECUTE lead_ranked(
    'lorem^4',
    '(ipsum^4 OR ipsum~1^1.4 OR ipsum*^2)'
);

SELECT id, tin.score(ctid) AS score
FROM lead_score_repro
WHERE title ==> 'lorem^4'
  AND title ==> '(ipsum^4 OR ipsum~1^1.4 OR ipsum*^2)'
ORDER BY id;

This gives the following:

I believe this is due to the first-query fallback in score_support() that causes this. combine_constant_queries() requires Const nodes and returns None for parameters. The caller then uses first_query, discarding the remaining expressions from scoring:

let combined_query = combine_constant_queries(&same_expression)
    .unwrap_or_else(|| pg_sys::copyObjectImpl(first_query.cast()).cast());

In EXPLAIN (VERBOSE, COSTS OFF), I see score_bound(title, $1, ...) for the parameterized query. For the literal query, I see both search expressions in the scorer's query argument.

Aggregating scores through a subquery raises a scoring-context error

CREATE TEMP TABLE lead_score_repro (
    id integer PRIMARY KEY,
    title text NOT NULL
);

INSERT INTO lead_score_repro VALUES
    (1, 'lorem ipsum'),
    (2, 'lorem ipsun');

CREATE INDEX ON lead_score_repro USING tin (title);
ANALYZE lead_score_repro;

-- Succeeds.
SELECT max(tin.score(ctid)) AS score
FROM lead_score_repro
WHERE title ==> 'lorem^4';

-- Fails.
SELECT max(score) AS score
FROM (
    SELECT tin.score(ctid) AS score
    FROM lead_score_repro
    WHERE title ==> 'lorem^4'
) AS matches;

For the direct aggregate, I get 0.72928625. For the subquery aggregate, I get:

ERROR: tin.score() requires a tin index scan and cannot be used in this query context
SQLSTATE: XX000