Add README

Author: TroyHernandez

README.md

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+# mx.api
+
+A minimal-dependency client for the
+[Matrix Client-Server HTTP API](https://spec.matrix.org/), suitable for
+talking to a Synapse or Conduit homeserver from R. Two Imports: `curl`
+and `jsonlite`. No tidyverse.
+
+Pairs with [`mx.crypto`](https://github.com/cornball-ai/mx.crypto),
+which handles Olm + Megolm; mx.api itself does no cryptography.
+
+## Install
+
+```r
+# CRAN
+install.packages("mx.api")
+
+# GitHub (development version, 0.1.0.1)
+remotes::install_github("cornball-ai/mx.api")
+```
+
+## Quick start: log in, send, sync
+
+```r
+library(mx.api)
+
+s <- mx_login(
+    server   = "https://matrix.example",
+    user     = "alice",
+    password = "hunter2"
+)
+
+room <- mx_room_join(s, "#general:matrix.example")
+mx_send(s, room, "hello from R")
+
+batch <- mx_sync(s, timeout = 0)
+str(batch$rooms$join)
+
+mx_logout(s)
+```
+
+## What's covered
+
+| Area | Functions |
+|---|---|
+| Session | `mx_register`, `mx_login`, `mx_logout`, `mx_whoami`, `mx_session` |
+| Rooms | `mx_rooms`, `mx_room_create`, `mx_room_join`, `mx_room_leave`, `mx_room_members`, `mx_room_name`, `mx_room_topic` |
+| Messages | `mx_send`, `mx_messages`, `mx_sync`, `mx_react`, `mx_read_receipt` |
+| Media | `mx_upload`, `mx_download` |
+| E2EE transport | `mx_keys_upload`, `mx_keys_query`, `mx_keys_claim`, `mx_send_to_device` |
+| E2EE signing helper | `mx_canonical_json` |
+
+End-to-end **cryptography** is out of scope; pair with `mx.crypto`
+(or another crypto library) to sign and verify the payloads these
+endpoints carry. Helpful framing:
+
+- mx.api speaks Matrix HTTP. It does no signing, no key management,
+  no key validation.
+- mx.crypto speaks Olm + Megolm. It does no HTTP.
+- An integration script that wants encrypted rooms uses both. The
+  current reference is `mx.crypto/inst/integration/e2e_demo.R`.
+
+## Canonical JSON
+
+`mx_canonical_json()` is the byte-stable encoder Matrix's signing rules
+require. It is hand-rolled (not a jsonlite wrapper) so the
+spec-sensitive choices — key ordering by UTF-8 byte sequence, integer
+range, NaN/Inf/NA rejection, duplicate-key rejection, control-char
+escaping — are visible and unit-tested rather than hidden in another
+package's defaults.
+
+```r
+mx_canonical_json(list(b = 2, a = 1))
+#> [1] "{\"a\":1,\"b\":2}"
+
+mx_canonical_json(1.5)
+#> Error: mx_canonical_json: non-integer number 1.5 disallowed
+```
+
+97 assertions exercise the encoder (see `inst/tinytest/test_canonical_json.R`).
+
+## Status
+
+**0.1.0.1** dev marker on `main` (2026-05-13). The 0.1.0 release is on
+CRAN. The 0.1.0.1 delta is additive:
+
+- New transport endpoints for E2EE coordination:
+  `mx_keys_upload`, `mx_keys_query`, `mx_keys_claim`,
+  `mx_send_to_device`.
+- New `mx_canonical_json` for signature payload encoding.
+
+See `NEWS.md` for the full changelog.
+
+## CI
+
+GitHub Actions via [r-ci](https://github.com/eddelbuettel/r-ci); macOS
+and Ubuntu runners cover every commit + PR.
+
+## License
+
+MIT. See `LICENSE`.