feat(client/android): the eighth field carries the OS, and cards wear it

The JNI discovery record appends `os` as its eighth ␟-field (append-only —
the Kotlin parser's arity guard already tolerates both old and new records,
now pinned by tests in both directions), sanitized on the Kotlin side by the
mirrored chain grammar next to the shared `osIconTokens` walk. `KnownHost`
persists it additively (optString — no schema bump, migration passes it
through) with `learnOs` beside `learnMac`, learned on the same discovery tick.

Compose ships no brand icons, so OsIcons.kt vendors the ten marks as raw SVG
path strings built into ImageVectors via PathParser (lazy, cached) — they tint
with the Material theme like any Icon. The host card's address line leads with
the mark, live advert preferred over the stored chain.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/android/native/src/discovery.rs

@@ -31,9 +31,10 @@ const PROTO: &str = "punktfunk/1";
 /// Field separator inside one serialized record (ASCII Unit Separator — never in a field value).
 const FIELD_SEP: char = '\u{1f}';
 
-/// One resolved host, serialized to Kotlin as `key␟name␟addr␟port␟fp␟pair␟mac` (`␟` = [`FIELD_SEP`]).
-/// Records are newline-joined in a poll snapshot; [`Host::encode`] strips the framing bytes from
-/// every field so no value can break it.
+/// One resolved host, serialized to Kotlin as `key␟name␟addr␟port␟fp␟pair␟mac␟os`
+/// (`␟` = [`FIELD_SEP`]). Records are newline-joined in a poll snapshot; [`Host::encode`] strips
+/// the framing bytes from every field so no value can break it. New fields append (the Kotlin
+/// parser tolerates both arities), never reorder.
 #[derive(Clone, PartialEq)]
 struct Host {
     key: String,
@@ -44,6 +45,9 @@ struct Host {
     pair: String,
     /// Wake-on-LAN MAC(s) from the mDNS `mac` TXT (comma-separated), for later wake. Empty if absent.
     mac: String,
+    /// OS-identity chain from the mDNS `os` TXT (`linux/fedora/bazzite`, ...), for the host
+    /// card's OS icon. Empty if absent (older host).
+    os: String,
 }
 
 impl Host {
@@ -56,7 +60,7 @@ impl Host {
             s.replace(['\n', '\r', FIELD_SEP], "")
         }
         format!(
-            "{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}",
+            "{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}{FIELD_SEP}{}",
             clean(&self.key),
             clean(&self.name),
             clean(&self.addr),
@@ -64,6 +68,7 @@ impl Host {
             clean(&self.fp),
             clean(&self.pair),
             clean(&self.mac),
+            clean(&self.os),
         )
     }
 }
@@ -186,6 +191,7 @@ fn resolve(info: &ResolvedService) -> Option<Host> {
         fp: val("fp"),
         pair: val("pair"),
         mac: val("mac"),
+        os: val("os"),
     })
 }
 
@@ -206,7 +212,7 @@ pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeDiscoverySt
 }
 
 /// `NativeBridge.nativeDiscoveryPoll(handle): String` — the current resolved-host snapshot,
-/// newline-joined records of `key␟name␟addr␟port␟fp␟pair␟mac` (`␟` = U+001F). Empty string = no hosts /
+/// newline-joined records of `key␟name␟addr␟port␟fp␟pair␟mac␟os` (`␟` = U+001F). Empty string = no hosts /
 /// `0` handle. Poll ~1 Hz from the UI thread (cheap: a mutex lock + string build).
 #[no_mangle]
 pub extern "system" fn Java_io_unom_punktfunk_kit_NativeBridge_nativeDiscoveryPoll<'local>(
@@ -268,10 +274,11 @@ mod tests {
             fp: "ab".repeat(32),
             pair: "required".into(),
             mac: "aa:bb:cc:dd:ee:ff".into(),
+            os: "linux/fedora/bazzite".into(),
         };
         let encoded = h.encode();
         let fields: Vec<&str> = encoded.split(FIELD_SEP).collect();
-        assert_eq!(fields.len(), 7);
+        assert_eq!(fields.len(), 8);
         assert_eq!(fields[0], "host-123");
         assert_eq!(fields[1], "home-worker-2");
         assert_eq!(fields[2], "192.168.1.70");
@@ -279,6 +286,7 @@ mod tests {
         assert_eq!(fields[4], "ab".repeat(32));
         assert_eq!(fields[5], "required");
         assert_eq!(fields[6], "aa:bb:cc:dd:ee:ff");
+        assert_eq!(fields[7], "linux/fedora/bazzite");
         assert!(
             !encoded.contains('\n'),
             "a record must never contain the record separator"
@@ -297,12 +305,13 @@ mod tests {
             fp: "ab\u{1f}cd".into(),
             pair: "required\n".into(),
             mac: "aa:bb\u{1f}cc".into(),
+            os: "linux\u{1f}evil/arch".into(),
         };
         let encoded = h.encode();
         assert_eq!(
             encoded.matches(FIELD_SEP).count(),
-            6,
-            "exactly seven fields"
+            7,
+            "exactly eight fields"
         );
         assert!(!encoded.contains('\n') && !encoded.contains('\r'));
         let fields: Vec<&str> = encoded.split(FIELD_SEP).collect();
@@ -310,5 +319,6 @@ mod tests {
         assert_eq!(fields[1], "evilhost");
         assert_eq!(fields[4], "abcd");
         assert_eq!(fields[5], "required");
+        assert_eq!(fields[7], "linuxevil/arch");
     }
 }