NSQL Filter Language & Webhook Specification

Status: the parser, validator, and match engine are genuinely implemented. ON ACCOUNT scoping and non-ASCII rule parsing are correct (Phase 3.A, done). Actions still do not execute against live mail — the match-and-act engine is not yet wired into the sync path, and webhook dispatch (CALL WEBHOOK) is unwired end-to-end — and header (header['X-...']) conditions always evaluate false (hardcoded). These are tracked as roadmap M4.

Nuncio SQL Filter Language (NSQL) is a declarative, high-throughput email routing and automation language powered by sqlparser-rs.

1. NSQL Compiler Pipeline & Validation Flowchart

2. NSQL Syntax Grammar

The parser (crates/nuncio-filter/src/parser.rs) accepts an optional ON ACCOUNT clause, a sqlparser-parsed WHERE-style condition, and a comma-separated ACTION clause — not the WHEN/THEN form this section previously described:

/* Complete NSQL Statement Syntax */
[ON ACCOUNT '<target_account>']
[WHERE] <field> <operator> <value> [AND|OR <condition>]
ACTION <action_1> [, <action_2> ...];

Supported Fields & Operators

Fields: subject, from, to, body, header['X-Spam-Score'], has_attachment, size, folder, date, account.
Operators: =, !=, CONTAINS, NOT CONTAINS, MATCHES (regex), >, <, >=, <=, IN ('a', 'b'), NOT IN ('a', 'b').
Actions: MOVE TO 'folder', COPY TO 'folder', MARK READ, MARK UNREAD, FLAG, UNFLAG, DELETE, FORWARD TO 'email', CALL WEBHOOK 'url'.

3. Webhook Dispatch

CALL WEBHOOK actions dispatch through crates/nuncio-filter/src/webhook.rs: an outbound HTTP POST signed with an HMAC-SHA256 signature, with SSRF defenses on the target URL. As noted above, this dispatcher exists but is not yet invoked from the live sync path (roadmap M4). (A previous diagram in this section depicted the removed length-prefixed JSON-RPC IPC transport, not the webhook flow, and has been removed as inaccurate.)