query_graph Cypher evaluator: labels(), count(*), AS alias, and LIMIT all broken

[jjoos]

Summary

Four functional bugs in the hand-rolled Cypher subset evaluator (src/cypher/cypher.c) prevent query_graph from handling common Cypher patterns correctly. All observed against a v0.6.0 index on macOS arm64.

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D1. labels(n) always returns empty string

Repro:

MATCH (n) WHERE n.project = 'my-project' RETURN labels(n) LIMIT 1

Expected: {"labels(n)": ["Class"]} (or the node's actual label)
Actual: {"labels(n)": ""}

Likely cause: labels() function returns the raw label column (a single string) without wrapping it in a JSON array, or is unimplemented and returns the empty default.

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D2. count(*) aggregation dropped — empty result set

Repro:

MATCH (n:Function) WHERE n.project = 'my-project' RETURN count(*)

Expected: One row: {"count(*)": 12096}
Actual: Empty result set (0 rows).

The aggregate expression is either not recognized by the evaluator or its result is discarded during projection.

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D3. AS <alias> in RETURN clause ignored

Repro:

MATCH (n) RETURN n.name AS fn_name LIMIT 3

Expected: {"fn_name": "..."}
Actual: {"n.name": "..."}

The alias is parsed but not propagated to the output projection.

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D4. LIMIT ignored when paired with aggregate

Repro:

MATCH (n:Function) RETURN n.name, count(*) LIMIT 10

Expected: 10 rows (or fewer) with group counts.
Actual: All rows returned (or 0 rows per D2, depending on which bug fires first).

LIMIT appears to only apply on the non-aggregating execution path.

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Impact

These bugs make query_graph unreliable for agent use. We currently document Cypher limitations in our tool schemas rather than relying on query_graph for anything beyond simple MATCH (n:Label) WHERE ... RETURN n.name patterns.

Environment

• CBM v0.6.0, commit bebc6d8
• macOS arm64 (Apple Silicon), also reproduced on Linux x86_64 Lambda
• Index mode: full, repos from 2K to 215K nodes

Suggested approach

Each sub-bug is likely in a different part of the evaluator and could be fixed independently. Separate PRs per sub-bug would be easiest to review.

[filhocf]

Confirmed on v0.5.5 (Linux amd64). Reproduction:

MATCH (n) RETURN labels(n) AS type, count(*) AS total LIMIT 5

Expected: 5 rows with label names and counts (aggregated)
Actual: 750 rows (all nodes), all with empty string "" for labels. Multiple issues:

1. labels(n) returns "" instead of the node label
2. count(*) is not aggregated — returns one row per node
3. AS type alias is ignored — column name shows labels
4. LIMIT 5 is ignored — returns all 750 nodes

Tested with a project that has 750 nodes and 817 edges. Basic MATCH (n:Function) RETURN n.name LIMIT 5 works correctly, so the issue is specifically with Cypher functions and aggregation.

Will test again on v0.6.0 when I can restart the MCP process.