Stories you can answer, and an @ that finds people

The story features existed in the codec and nowhere a person could reach
them. ＋ went straight to the file chooser, so a story of words was
unreachable even though the engine could carry one; there was no way to
react, reply, mute, or see what anybody had said back.

＋ is a menu now. Reactions are a fixed row of five — a story is glanced
at and scrolled past, and anything that takes two taps to say "nice"
does not get used. Your own story shows the tally instead, because you
cannot react to yourself and a row of dead buttons is worse than none.

Mentions get an `@` picker in the group composer, matching iOS down to
the rule that matters: the id is recorded when somebody is PICKED, never
re-derived from the text at send time. Deriving it would mean typing a
name reached that person whether or not they were chosen, and renaming a
contact would silently unmention them. Only the ones still named in the
body are sent, so picking somebody and then deleting their name doesn't
ring them about a message that no longer mentions them.

A group member who isn't in your contacts has no name to show, so they
appear under their id. Un-mentionable would be worse than ugly — it
would mean a group where some people cannot be reached.

Mentions on Android are carried and rendered but override nothing: there
is no per-conversation notification mute here to override yet.

640 unit tests green across app, engine and client. PARITY.md updated —
mentions and the story features move to ✅, and Files and Wallet get rows
saying plainly that Android has none of either.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

engine/src/main/kotlin/io/flamenet/e2e/Vault.kt

@@ -82,6 +82,7 @@ class Vault(private val storage: Storage, private val key: SecretKey) {
         private const val OUTBOX = "outbox"
         private const val CALL_LOG = "call-log"
         private const val STORY_AUDIENCE = "story-audience"
+        private const val STORY_MUTES = "story-mutes"
         private const val DISAPPEAR = "disappear"
         private const val SNOOZE = "snooze"
         private const val REPLY_REMINDER = "reply-reminder"
@@ -1091,6 +1092,25 @@ class Vault(private val storage: Storage, private val key: SecretKey) {
 
     fun saveStoryAudience(audience: JSONObject) = writeJson(STORY_AUDIENCE, audience)
 
+    /**
+     * Whose stories this device does not show.
+     *
+     * 🔴 Encrypted at rest with everything else in here. Who somebody has
+     * quietly stopped watching is exactly the kind of thing a stolen phone
+     * should not hand over — and it is a judgement about a person, which is
+     * worse to leak than a preference.
+     */
+    fun storyMutes(): Set<Long> {
+        val array = readJson(STORY_MUTES)?.optJSONArray("ids") ?: return emptySet()
+        return (0 until array.length()).map { array.optLong(it) }.toSet()
+    }
+
+    fun saveStoryMutes(ids: Set<Long>) {
+        val array = org.json.JSONArray()
+        ids.sorted().forEach { array.put(it) }
+        writeJson(STORY_MUTES, JSONObject().put("ids", array))
+    }
+
     // -- Key-log issuer pin (audit M1) ---------------------------------------
 
     /**