fix(graph-node): execute Cypher MATCH properly and defer hydration (#879, #826)

[ruvnet]

Closes #879. Closes #826.

What was broken

query() handled exactly one shape — MATCH (n:Label) — through the label index. Every other shape hit an empty if branch and returned zero rows:

• MATCH (n) — the label-less scan, which graph-node: persisted writes invisible to stats()/query() across handles/processes; MATCH without label unimplemented #879 calls "the standard query shape for point lookups"
• any WHERE filter — the parser produced a where_clause (cypher/ast.rs:38, populated at parser.rs:142) that the executor dropped on the floor
• every relationship pattern — result_edges was declared and never written to, so edges was [] for all query shapes, labelled ones included

querySync() was worse: it never called parse_cypher at all. It returned a hardcoded empty result for any input, including the query in its own doc example.

What this does

New cypher_exec module — a single-pattern matcher (not a planner):

shape	before	after
MATCH (n)	[]	full node scan
MATCH (n:Label)	worked	unchanged
WHERE n.id = 'x'	ignored	evaluated
WHERE n.age > 30 AND ...	ignored	evaluated
MATCH (a)-[r:T]->(b)	edges: []	edges + endpoints, direction honoured
MATCH (n {name: 'x'})	ignored	evaluated
CREATE ... via query()	silently dropped	refused with an error
[*1..2], chained patterns	silently []	error naming what was refused

query() and querySync() now share one executor so they cannot drift apart again.

The last row matters as much as the rest: returning an empty set for something you can't execute is what let this ship through three releases without anyone noticing.

Hydration (#826)

#879 asks for a release. That was blocked: the fix for #879's claims 1/2 (already on main, commit 31bb94401) calls hydrate_from_storage synchronously from the NAPI constructor, replaying the whole store on the Node main thread — ~15s of blocked event loop on the 154k-node graph from #810. Shipping #879 alone would have traded "persistence is invisible" for "constructing a handle freezes your process".

Hydration now runs once, lazily, inside the spawn_blocking of whichever operation needs it first. Construction is O(1) again. deferred_hydration_replays_exactly_once covers the hazard that introduces — replaying twice and double-counting every record.

Also

• Internal __embedding / __confidence no longer leak into result rows. A 384-element float dump was landing in every property map — invisible until query() started returning rows.
• Scalar properties render as alice, not String("alice") (was format!("{:?}")).
• test.js now asserts. It ran await db.query('MATCH (n) RETURN n') — precisely the broken shape — logged the result and printed ✓ Query executed regardless. Test 12 reopened a persisted DB and never checked the reopened handle at all. That is the mechanism by which this reached 2.0.4.
• Regenerated index.d.ts, which had drifted from the implementation: deleteNode, deleteEdge, deleteHyperedge and their result types existed in Rust but were absent from the published types.
• Corrected stream doc examples calling db.queryStream() / db.searchHyperedgesStream() — neither method exists on GraphDatabase, and QueryResultStream::next() is itself a stub returning Ok(None).

Verification

• cargo test -p ruvector-graph-node — 21 passed (was 8; 13 new)
• cargo test -p ruvector-graph --features storage — 259 passed
• node test.js — 12 sections, now with assertions
• clippy clean, cargo fmt --check clean
• graph-node: persisted writes invisible to stats()/query() across handles/processes; MATCH without label unimplemented #879's verbatim repro re-run against a release build: all three handles (g1, second same-process handle, GraphDatabase.open) report totalNodes: 1, and a fresh process agrees

Out of scope, filed separately

The parser binds NOT tighter than comparison, so NOT n.age = 30 arrives as (NOT n.age) = 30. That is a precedence defect in ruvector-graph's parser affecting every consumer, not just this binding — it deserves its own change rather than riding along here.

Version bumped to 2.1.0 (minor: query() gains behaviour, and unsupported constructs now error where they previously returned empty).

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https://claude.ai/code/session_017cMsrUW5PFR9fPahCwT5iA