Goblin Build 133 - Tor transport (replaces the Nym mixnet)

The wallet's private transport moves from the Nym mixnet to embedded Tor
(arti, copied from GRIM's engine): it dials the relay's pinned .onion, so
the relay never learns your IP, while the relay + NIP-59 gift-wrap hide the
rest - content, sender, and (via a relay-side randomized release) timing.
The Grin node stays on the clear internet as before.

Why leave the mixnet: the Nym free-tier bandwidth this depended on is being
removed upstream (the grant expires at UTC midnight; the paid path requires
holding NYM tokens), so a payments wallet can't stand on it. Tor is
unmetered, embedded in-process on mobile, faster where users wait, and
lighter on the battery.

Preserved intact: the confirm-before-sent guard, relay-gated readiness, and
the lazy warm-on-activity node polling. src/nym/ is feature-gated off (arti
and nym-sdk can't share one binary); full removal is a follow-up.

Cargo.toml

@@ -31,6 +31,17 @@ lto = true
 codegen-units = 1
 panic = "abort"
 
+[features]
+## Default build uses the Tor transport only. The `nym` feature gates the dormant
+## mixnet path (src/nym/). Cargo resolves OPTIONAL deps into the graph too, so
+## nym-sdk cannot merely be `optional` — it links a different libsqlite3-sys than
+## arti (a native-lib `links` conflict Cargo rejects at resolution). The nym
+## path-deps are therefore commented out below; the module code is retained on
+## disk but building `--features nym` requires restoring them (and drops arti —
+## the two transports cannot coexist in one binary, which is why Tor replaced Nym).
+default = []
+nym = []
+
 [dependencies]
 log = "0.4.27"
 
@@ -124,18 +135,34 @@ rustls = { version = "0.23", features = ["ring"] }
 tokio-rustls = { version = "0.26", default-features = false, features = ["ring"] }
 webpki-roots = "1"
 
-## Nym mixnet, linked IN-PROCESS (no sidecar subprocess, no bundled binary).
+## Tor — embedded arti (the DIALING half only: connect OUT to the relay's .onion,
+## and to clearnet HTTP hosts through a Tor exit). Copied from our sister wallet
+## GRIM's proven, shipping engine. Two choices inherited VERBATIM from GRIM: arti
+## 0.43 across the family, and the native-tls Tor runtime (TokioNativeTlsRuntime),
+## NOT rustls — this deliberately sidesteps the rustls/ring crypto-provider
+## conflict fought during the Nym era (our relay/HTTP rustls still uses ring, see
+## lib.rs; arti's own TLS is native-tls and never touches the rustls provider).
+## `static` vendors openssl (self-contained Android/cross builds, as GRIM ships);
+## `onion-service-client` enables dialing .onion. We drop GRIM's `pt-client`
+## (bridges) and `onion-service-service` (hosting) — Goblin only dials.
+arti-client = { version = "0.43.0", features = ["static", "onion-service-client"] }
+tor-rtcompat = { version = "0.43.0", features = ["static"] }
+
+## Nym mixnet — DORMANT since the Tor transport swap. The mixnet path (src/nym/)
+## is retained on disk but its deps are COMMENTED OUT, because arti's `tor-dirmgr`
+## needs libsqlite3-sys 0.34 (rusqlite 0.36) while nym-sdk's credential-storage
+## needs libsqlite3-sys 0.30 (sqlx) and BOTH link the native `sqlite3` library —
+## Cargo forbids two packages linking the same native lib, and it rejects this at
+## RESOLUTION even for optional/unused deps. The two transports therefore cannot
+## coexist in one binary (exactly why Tor replaced Nym). To build the old path,
+## restore these three deps and build `--features nym` (which then drops arti).
+## Full deletion is a later phase; for now the code stays on disk for reference.
 ## Path deps into the local nym checkout, PINNED at rev
-## f6ed17d949cc19fee0fb51db3cb65771fd510d5b: it carries the load-bearing local
-## commit "http-api-client: preconfigured webpki roots on Android". Do not
-## float the checkout past that rev without re-verifying the Android build.
-nym-sdk = { path = "../nym/sdk/rust/nym-sdk" }
-## smolmix: TCP/UDP tunnel over the mixnet with an AUTO-SELECTED IPR exit —
-## the single-network-requester SPOF is structurally gone (plan G14).
-smolmix = { path = "../nym/smolmix/core" }
-## mix-dns wire codec. Already in the dependency graph via nym-http-api-client
-## (Cargo.lock), so we reuse it instead of vendoring a DNS encode/parse.
-hickory-proto = { version = "0.26", default-features = false, features = ["std"] }
+## f6ed17d949cc19fee0fb51db3cb65771fd510d5b ("http-api-client: preconfigured
+## webpki roots on Android").
+# nym-sdk = { path = "../nym/sdk/rust/nym-sdk" }
+# smolmix = { path = "../nym/smolmix/core" }
+# hickory-proto = { version = "0.26", default-features = false, features = ["std"] }
 
 ## NIP-98 payload hashing
 sha2 = "0.10.8"