EXEC Schemes and Builtins

The schemes

Scheme	Runs	Reference
http(s)://…	Your service, over HTTP	ops
op://NAME	Sandboxed wasm nano-op on the chassis	ops, sdk/op
txco://…	A chassis builtin (table below)	this page
ai://chat	A chat model via the chassis’s AI registry	ai
mcp+http(s)://…	A tool on an external MCP server	mcp
<stack>/<scope>	Unschemed stage jump (synthesized into @goto)	resonators

The builtin registry

Builtin	What it does
txco://noop	Returns {}. Placeholder / structural.
txco://static	Serve static files with layered lookup: the stack’s FILES/ → workspace FILES/ → embedded defaults. Caps: 1 MiB/file, 2048 files, 64 MiB total. See examples/quickstart-hello-world for the rule pattern.
txco://read-file	Read a stack’s FILES/ asset(s) into the document as data (templates, fixtures, config) — the read-into-the-tree counterpart to static. See read-file.
txco://web-render	Read a source path, optionally render Markdown→HTML, set @web.res.*, halt. Pages without a backend.
txco://sendmail	Render + submit outbound email from the _sendmail contract — see sendmail.
txco://relay	Forward an inbound message VERBATIM (the .forward primitive) — see relay. Only fires from the inbound-mail path (LMTP).
txco://hmac-sign	Compute an HMAC signature (key via WITH secrets.*).
txco://hmac-verify	Verify an HMAC, constant-time; result lands under @computed.*.
txco://basic-auth-encode	Encode user:pass to a basic-auth header value.
txco://basic-auth-verify	Check an inbound Authorization: Basic … header against a user and a secret password, constant-time; only the verdict lands under @computed.* (basic_auth_ok, basic_auth_configured). With secrets.password.optional = true + allow_unconfigured = true an unset secret leaves the route open — the demo/dev shape.
txco://copy	Path-to-path copy inside the envelope (what SET can’t do with computed paths).
txco://kv/get · kv/set · kv/delete · kv/incr · kv/cas	Read + write durable state across requests — counters, flags, locks, caches (boltdb local / redis shared). See kv.
txco://blob/put · blob/get · blob/stat · blob/list · blob/delete	Runtime-writable BYTES under mutable, permissioned names over the content-addressed store — uploads, documents, artifacts; seeded with a stack via BLOBS/. See blobs.
txco://notebook/append · notebook/read · notebook/export · notebook/list · notebook/delete	An append-only record per (tenant, namespace, name) — task history, conversation history, audit breadcrumbs — read back by cursor, time window or tail (always oldest first) and exported as NDJSON. A duplicate object_key returns the original entry. See notebooks.
txco://imap/account · imap/append · imap/mailbox · imap/remove · imap/flags · imap/list · imap/messages · imap/get	Provision an IMAP account (argon2id, its INBOX), materialize messages (a RECORD or verbatim bytes) into mailboxes the imap personality serves to any mail client, manage role-tagged folders with per-verb policy, and read the store back. See imap.
txco://websocket/accept · websocket/send · websocket/reply · websocket/close	Live sessions: in the upgrade request’s own run, accept takes the connection (WITH state, origins, subprotocols, events); then every message is one run of <stack>/_websocket and reply (or send by session_id) writes back on the socket. See websocket.
txco://detect-tenant	Boot-pipeline: hostname/listener → tenant resolution. Used by the scaffolded _sys/boot rules; you rarely call it directly.
txco://route	Boot-pipeline: promote a routing proposal (@route.*) into @goto + @tenant. Companion to detect-tenant.
txco://continuation-result	Poll handler behind ?_txc.continuation=<id> (continuations). Wired by the chassis; not called from rules.

Builtins pay normal fuel and appear in traces like any other op.