fix: add close() so a file-backed db can be released deterministically

[adityamukho]

Fixes the Node.js CI failure on main after the v1.2.2 cascade — file-backed roundtrip broke on all four platforms.

Why it broke

minigraf 1.2.2 (project-minigraf/minigraf#304) refuses a second handle on a file this process already has open. Two handles each cache their own header.page_count, allocate pages from it, and bounds-check reads against it, so they diverge and corrupt the file — that was the source of the intermittent Page N out of bounds. Refusing is correct.

The problem is that this binding had no way to release a handle. The class exposed only constructor, inMemory, execute and checkpoint. Every other binding already has an escape hatch:

binding	release mechanism
Python, Java, Swift (UniFFI)	destroy()
C	minigraf_close
Node (napi-rs)	none

So the existing test was not doing anything wrong:

{
  const db = new MiniGrafDb(dbPath)
  db.execute('(transact [[:bob :name "Bob"]])')
  db.checkpoint()
}                                  // correct in a refcounted host

const db2 = new MiniGrafDb(dbPath) // throws: first handle is still alive

Leaving the block makes db unreachable but frees nothing — V8 collects whenever it likes, which here is well after the reopen. In Python or Rust scope exit releases the handle; in JavaScript it cannot. The consequence was that Node users could not reopen a .graph file in one process at all, with no workaround available.

For contrast, minigraf-java's equivalent test passes precisely because it calls db.destroy() between the two opens.

The fix

close() drops the inner Minigraf, running its Drop impl (best-effort checkpoint, then release of the sidecar .graph.lock). inner becomes an Option so that is representable. It is idempotent, and execute() / checkpoint() throw database is closed afterwards.

Tests

file-backed roundtrip now closes before reopening. Removing that single call reproduces the CI failure exactly — verified locally — so close() is what fixes it rather than something incidental:

✖ file-backed roundtrip
  Error: Database is already open in this process (lock file: /tmp/…graph.lock,
  holder PID: 58474 == our own). …

Three new cases: reopening without close throws, close is idempotent, and use-after-close throws. Full suite 6/6 locally against minigraf 1.2.2 from crates.io; cargo clippy -D warnings and cargo fmt --check clean.

Note on index.js

Left untouched on purpose. Regenerating it locally produces ~200 lines of churn unrelated to this change (node:fs → fs, optional chaining stripped, a stale 1.1.1 version string baked into the mismatch check) because my @napi-rs/cli minor differs from CI's. index.d.ts is included since its diff is purely the new close() and doc comments. CI regenerates both during its own build.

Follow-up, not in this PR

minigraf@1.2.2 is already published to npm — the Release workflow succeeded before CI failed — so the version on the registry has this gap. It needs a 1.2.3 once this lands.

🤖 Generated with Claude Code

https://claude.ai/code/session_01QRGNkzJc5FdfpbzAh4ZZzK