# Platform flags

Things known or suspected to behave differently outside Windows, plus deployment gotchas that
have already cost time once. **Development and testing are currently Windows-only**, so anything
here marked *unverified* has not run on the platform in question and must not be assumed to work.

Each entry says what the risk is, why it matters, and what to do about it. Delete an entry when it
has been verified or made moot — not when it merely stops being convenient.

## Cryptography

**`ChaCha20Poly1305.IsSupported` is false on macOS**, and on Windows builds before 10.0.20142.
This is why the client uses NSec (libsodium) rather than the BCL for content encryption; see
docs/crypto.md §1. *Already mitigated* — but if a BCL AEAD path is ever added as a fallback it
**must** gate on `IsSupported` rather than assuming availability, or the client will fail to open
any vault on macOS.

**Argon2id timings are measured on one Windows machine only.** 256 MiB with t=4 took 323 ms here.
The floor and ceiling in `EnrollmentLimits` were chosen against that number. *Unverified
elsewhere:* recalibrate on the slowest target platform before recommending a default profile,
because a cost that is comfortable on a desktop can make unlock unusable on a low-power laptop —
and the parameters are stored per user at enrollment, so a bad default is a per-user migration.

**libsodium ships native binaries per RID.** This complicates single-file and AOT publishing, and
on macOS every native library (`libsodium`, `libSkiaSharp`, `libHarfBuzzSharp`, `libe_sqlite3`)
must be signed **individually** with `--options runtime --timestamp` before the bundle is signed,
or notarization fails with an error that does not name the offending file.

## Desktop client

**The Avalonia WebView on Linux is unproven, and is the single largest risk in the plan.** The
official control uses WPE WebKit (`libwpewebkit-2.0`); the community `NativeWebView` uses WebKitGTK
(`libwebkit2gtk-4.1`), which is far more widely installed. Avalonia's own documentation
contradicts itself on whether offscreen rendering works there. *Unverified:* the spike must cover
Ubuntu on both Wayland and X11, Fedora KDE, and macOS 15. This is why the terminal sits behind
`ITerminalHost` — that abstraction is what preserves the option to swap backends, and it should
not be collapsed away for convenience.

**SSH.NET's `window-change` on `ShellStream` is unverified.** A terminal that cannot resize is
unusable, so this gates M1's client work. Fall back to `IChannelSession` if it does not work, and
prefer forking and upstreaming a fix over reflection as a long-term answer.

**MSIX packaging is ruled out, not merely deprioritised.** A packaged app runs WebView2 in an
AppContainer where loopback connections are blocked without a `CheckNetIsolation` exemption. The
terminal data plane *is* a loopback WebSocket, so MSIX would break the product outright. Velopack
for Windows/macOS/AppImage; Flatpak and deb/rpm defer updates to the package manager.

**Linux ships AppImage and Flatpak first**, specifically so the WebKit runtime is bundled rather
than assumed present on the user's machine.

## Build and CI

**Integration tests need a Docker daemon** (Testcontainers). They run on `ubuntu-latest` in CI.
macOS runners have no Docker daemon, and the Windows CI job is deliberately build-only. So
anything proved by an integration test is proved on Linux only — which is the right place for
server code, and no coverage at all for client platform behaviour.

**`[CallerFilePath]` is rewritten to `/_/...` under `ContinuousIntegrationBuild`.** Any test that
locates a fixture by source path passes locally and fails in CI. Copy fixtures to the output
directory and read them via `AppContext.BaseDirectory` instead; `GoldenVectorTests` shows the
pattern.

**`dotnet format --verify-no-changes` is part of the CI gate** and exits non-zero on style
warnings, not just whitespace. Run it before pushing; a build with zero warnings can still fail
that step.

## Deployment

**PostgreSQL 18 moved its data directory** to `/var/lib/postgresql`, not `/var/lib/postgresql/data`
as in 17 and earlier. A compose file carried over from an older version silently gets an empty
volume — the database appears to work and loses everything on restart. Relevant to any compose
file other than `deploy/docker-compose.dev.yml`, which is already correct.

**Keycloak in the dev stack listens on host port 18080, not 8080.** On this machine an unrelated
Apache Tomcat holds `127.0.0.1:8080`, and a loopback-specific bind wins over Docker's `0.0.0.0`
publish when resolving `localhost` — so every realm request returned 404 while the container
looked healthy. If discovery fails against a locally-published container, check for another
process bound specifically to loopback before suspecting the container.

**`Sync:CursorSigningKey` generates an ephemeral per-process key when unset.** Fine for a single
node; on a multi-node deployment cursors issued by one node are rejected by another, so clients
resync from the beginning repeatedly. Must be configured explicitly before running more than one
instance. `WarnOnRiskyConfiguration` logs this at startup.

**Rate limiting is not implemented yet** (M2). `POST /api/v1/me/enrollment` and the sync endpoints
are reachable by any authenticated caller at any rate. Enrollment requires a valid access token
and is idempotent, so the exposure is resource consumption rather than a credential-guessing
surface — but it is still an unmetered write path.

**`/api/v1/me` does not update `last_seen_at_utc`.** Deliberate: a GET that writes on every call is
a smell, and nothing depends on the value yet. Revisit when device management lands, since that is
the first feature that needs it.