feat(sea): execute statements asynchronously (submit + poll) for Thrift runAsync parity

[msrathore-db]

What

Brings the SEA execution path to the Thrift backend's always-async model (runAsync: true). Previously the SEA backend used the blocking napi executeStatement (the kernel polled to terminal internally), so:

• SeaOperationBackend.status() synthesized a constant FINISHED_STATE — it never reflected the real server state.
• A long-running query could not be cancelled from JS until it returned, because execute() blocked the call.

The Thrift backend submits, gets a pending operation handle back immediately, and polls getOperationStatus to a terminal state inside waitUntilReady(). This PR makes SEA do the same.

Changes

• SeaSessionBackend.executeStatement → calls the napi submitStatement (kernel wait_timeout=0s), receiving a pending AsyncStatement. Metadata methods keep the blocking statement path (the kernel returns those already-terminal).
• SeaOperationBackend now accepts either { asyncStatement } (query path) or { statement } (metadata path):
  • waitUntilReady() polls status() to a terminal state, firing the progress callback each tick (mirrors the Thrift getOperationStatus loop, delay(100)), then materialises the result stream via awaitResult().
  • status() maps the kernel StatementStatus (Pending/Running/Succeeded/Failed/Cancelled/Closed) to the matching TOperationState.
  • A Failed statement surfaces the kernel's typed SQL-error envelope via awaitResult()'s rejection (status() only carries the variant name).
• SeaNativeLoader gains the typed async surface: submitStatement, SeaNativeAsyncStatement, SeaNativeAsyncResultHandle, SeaNativeStatementStatus.

Why a JS-side poll loop (not a single blocking awaitResult)

The kernel AsyncStatement serialises its methods behind one tokio mutex. A single in-flight awaitResult() would hold that mutex for the entire query and queue cancel() behind it — so cancel couldn't interrupt a running query. Polling status() releases the mutex between ticks, leaving gaps for cancel() to land. This is what restores mid-run cancel parity.

Depends on

Kernel PR databricks/databricks-sql-kernel#76 (submitStatement + AsyncStatement napi surface). The native binding must be built from a kernel that includes #76.

Downstream fixes / reviewer note

• This PR supersedes the closed feat(sea): type async-execute napi surface + pecotesting e2e #394 and is the canonical async-execute fix. Later feat(sea): expose TLS verification toggle + custom CA on ConnectionOptions #407/feat(sea): wire rowLimit + statementConf + TIMESTAMP_NTZ/LTZ params #408 only add TLS and remaining statement-option/param surfaces on top; they do not replace this submit+poll lifecycle.
• If reviewing lower PRs that synthesize FINISHED_STATE or cannot cancel a long-running query mid-flight, that bug is fixed here.
• 2026-06-01 review-fix cascade: this async-execute branch now carries the [SEA-NodeJS] (7/8) Operation lifecycle — cancel / close / finished + INTERVAL parity + napi relocation #384 operation fixes: declared flatbuffers, one-pass IPC duration rewrite, cancel/close local-state rollback on native RPC failure, closed fetch → OperationStateError(Closed), and Arrow duration rewriter cleanup.
• 2026-06-01 review-fix cascade: this branch also uses native sessionId/statementId typing where available and rejects unsupported per-statement useCloudFetch instead of silently dropping it.

Testing

• 215 SEA unit tests pass, including a new async-lifecycle block in SeaOperationBackend.test.ts (poll-to-terminal with per-tick callback, real RUNNING status, Failed → kernel error, mid-run cancel → OperationStateError).
• Live A/B against a real warehouse (Thrift vs SEA, identical query): cancelling a long-running range(1e11) CROSS JOIN range(1000) mid-flight — both backends report mid-run operationState = 2 (RUNNING) and throw the identical OperationStateError: The operation was canceled by a client. Basic SELECT and a 5000-row multi-batch fetch also verified end-to-end on the async path.

Supersedes

PR #394 (feat(sea): type async-execute napi surface + pecotesting e2e), which only typed the surface on the earlier M0 backend and did not wire the async lifecycle.

This pull request and its description were written by Isaac.