Paul HittandClaude Opus 4.8
dc1be35816
🔴 **The obvious implementation is the one that must not be built.** Having each recipient fetch the URL to draw a card tells the site the reader's IP address, that they received a link, and roughly when they opened it — once per member on a group message. A messenger that hides the message and then has every reader announce its contents to a third party has given away what it was protecting. So the SENDER fetches, and the preview travels inside the ciphertext. The receiver renders from those bytes and contacts nobody. ⚠️ Sender-side is a smaller leak, not no leak: the site learns somebody is about to share that URL, from this address. The setting exists for that, and the copy says who learns what rather than implying it is free. 🔴 **The host is shown separately and derived from the URL**, because title and description come from a page the sender did not write — a card claiming one destination while the link points at another is a phishing primitive. Both fields are bounded on the way IN as well as line-limited at render, so the cap does not depend on a future renderer remembering one. ⚠️ `Content.text` still returns the raw body byte-for-byte when there is no preview, so an ordinary message is unchanged on the wire and older clients see exactly what they saw before. ⚠️ The fetch is short-timeout and best-effort, and runs on the IO context. A preview is a decoration and must never be able to delay a send — every failure path ends as a message with a plain URL in it. engine 168, client 96, app 40. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Flamenet Messenger — Android
The Android app, and the two libraries under it.
engine/ the protocol: X3DH, Double Ratchet, sealed sender, safety numbers,
key transparency. Plain Kotlin/JVM — no Android in it at all.
client/ the relay transport: HTTP, auth, the §8 routes.
app/ the Compose app.
interop/ the cross-engine driver; not shipped.
engine and client are deliberately plain JVM libraries. The protocol has
nothing to do with Android, and keeping it off the platform means their tests
run anywhere a JVM does — no SDK, no emulator, no device, which is also what
lets them gate in CI on Linux:
./gradlew :engine:test :client:test
The app's own unit tests need the Android SDK but still no emulator (Robolectric):
./gradlew :app:testDebugUnitTest
Where it stands
PARITY.md is the definition of done for this app — read that, not this. Every row there names the iOS file it came from so it can be re-checked rather than trusted. Headlines as of 2026-08-28: messaging, groups, attachments, voice notes, stories, calls, sealed sender, key transparency and the encrypted vault are built and tested; a cross-platform round trip against iOS was verified on 2026-08-26.
⚠️ This file said "Nothing here is an app yet" until 2026-08-28, above a tree containing the finished app — the README described the repository as it was when the engine landed and nothing updated it as the app grew around it. If a claim here ever disagrees with PARITY.md or with the tree, believe those, and fix this.
Why the engine came first, and is held to the vectors
An Android client needs the protocol implemented a third time, and the third
implementation is the one that finds the places where the specification says
less than the two existing engines quietly agreed on — but only if it is
written against the spec and the published vectors rather than against a
reading of our own Swift and JavaScript. So the engine is held to
test/vectors/protocol-v1.json in
flamenet-e2e — the same file the
other two engines are checked against, read from that repository rather than
copied here, because a copied vector file drifts and a drifting vector file
stops being a check. PublishedVectorsTest looks for it beside this checkout
and fails loudly if it cannot find it; FLAMENET_VECTORS overrides the search.
Two implementations that agree may both be wrong in the same way, especially when one was written while reading the other. The audit-path ordering in §19 is the worked example: a top-down reading of a bottom-up path produces the correct root for every left-spine index, so it passes any test that only checks index 0. The vector file pins a right-descending index for that reason, and the Kotlin tests assert both that the published path verifies and that the same path reversed does not.
If this engine ever disagrees with the file, the interesting question is which of the three is wrong — not this one by default.
Contributing and security
- CONTRIBUTING.md — building (JDK 21,
JAVA_HOMEis not optional on a Mac), the test gate, and the platform traps that cost an hour each. - PARITY.md — what iOS does, what this does, and what is left. It is the definition of done for this app.
- SECURITY.md — threat model and where to send a vulnerability report. Not an issue tracker matter: security@flamenetmessenger.com.