fix(formatting): resolve overlapping rich-text matches before rendering

findAllMatches() only cross-checks each match type against mentions (and
bolt11/lnurl against url+lightning); it never checks url against cashu, or
any other combination the ad-hoc per-type guards didn't anticipate. An
ordinary message containing a URL whose path embeds a "cashuA..."-shaped
token (e.g. a mint redemption link) produces two overlapping matches for
the same text -- the whole URL, and the nested cashu token inside it.

formatContent's single linear rendering pass assumes matches are
non-overlapping with strictly increasing ranges. Given the nested pair, it
appends the URL's full text, then unconditionally re-appends the nested
cashu substring a second time (styled differently), and walks its cursor
backward to the cashu match's end -- which is before the URL's actual end.
The trailing "remaining text" check then re-appends the tail of the URL a
third time, since the cursor never advanced past it.

Add a final pass that sorts matches by start position and greedily keeps
only non-overlapping ones, dropping any later match whose start falls
inside an already-kept match's range. This fixes the url/cashu case and
generally guards any other pair of match types that isn't already handled
by an explicit per-type check, without touching the existing exclusion
logic.

bitchat/Services/MessageFormattingEngine.swift

@@ -368,8 +368,25 @@ final class MessageFormattingEngine {
             allMatches.append(ContentMatch(range: match.range(at: 0), type: .lnurl))
         }
 
-        // Sort by position
-        return allMatches.sorted { $0.range.location < $1.range.location }
+        // Sort by position, then drop any match that overlaps one already
+        // kept. The per-type checks above only guard specific known pairs
+        // (e.g. bolt11/lnurl against url/lightning) -- they don't cover every
+        // combination, so an ordinary message can still produce overlapping
+        // matches of two OTHER types the checks never compared (e.g. a URL
+        // whose path embeds a "cashuA..."-shaped token). formatContent's
+        // single linear pass assumes non-overlapping, strictly-increasing
+        // ranges; without this pass a nested match re-renders already-shown
+        // text and can walk `lastEnd` backwards, duplicating a trailing
+        // slice of content a second time.
+        let sorted = allMatches.sorted { $0.range.location < $1.range.location }
+        var resolved: [ContentMatch] = []
+        var occupiedUntil = 0
+        for match in sorted {
+            guard match.range.location >= occupiedUntil else { continue }
+            resolved.append(match)
+            occupiedUntil = match.range.location + match.range.length
+        }
+        return resolved
     }
 
     private static func formatPlainContent(_ content: String, baseColor: Color, isSelf: Bool) -> AttributedString {

bitchatTests/MessageFormattingEngineTests.swift

@@ -349,6 +349,32 @@ struct MessageFormattingEngineTests {
 
         #expect(String(formatted.characters) == "<@alice> \(longContent) [\(message.formattedTimestamp)]")
     }
+
+    @MainActor
+    @Test func formatMessage_urlContainingCashuTokenIsNotDuplicated() {
+        // Bug: a URL match and a Cashu match are never cross-checked for
+        // overlap, only each independently against mentions. A URL whose
+        // path embeds a "cashuA..."-shaped segment (a perfectly ordinary
+        // mint redemption link) produces two overlapping matches; the
+        // single linear rendering pass then re-renders the nested cashu
+        // substring a second time and, because it walks `lastEnd` backwards,
+        // re-renders the URL's own trailing segment a third time.
+        let context = MockMessageFormattingContext(nickname: "carol")
+        let cashuToken = "cashuA" + String(repeating: "a", count: 44)
+        let url = "https://mint.example.com/redeem/\(cashuToken)/confirm"
+        let content = "redeem link \(url) now"
+        let message = BitchatMessage(
+            id: "url-cashu",
+            sender: "alice",
+            content: content,
+            timestamp: Date(timeIntervalSince1970: 1_700_001_111),
+            isRelay: false
+        )
+
+        let formatted = MessageFormattingEngine.formatMessage(message, context: context, colorScheme: .light)
+
+        #expect(String(formatted.characters) == "<@alice> \(content) [\(message.formattedTimestamp)]")
+    }
 }
 
 @MainActor