Expand coverage for transport, chat, and media flows (#1056)

* Expand coverage for transport, chat, and media flows

* Stabilize transport and media coverage tests

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchatTests/Services/AutocompleteServiceTests.swift

@@ -0,0 +1,50 @@
+import Foundation
+import Testing
+@testable import bitchat
+
+@Suite("AutocompleteService Tests")
+struct AutocompleteServiceTests {
+
+    @Test("Mention suggestions are sorted, capped, and include replacement range")
+    func mentionSuggestionsAreSortedAndCapped() {
+        let service = AutocompleteService()
+        let text = "hi @al"
+
+        let result = service.getSuggestions(
+            for: text,
+            peers: ["zoe", "alice", "albert", "bob", "alex", "ally", "alpha"],
+            cursorPosition: text.count
+        )
+
+        #expect(result.suggestions == ["@albert", "@alex", "@alice", "@ally", "@alpha"])
+        #expect(result.range == NSRange(location: 3, length: 3))
+    }
+
+    @Test("Suggestions are empty when cursor is not at a trailing mention")
+    func suggestionsRequireTrailingMentionContext() {
+        let service = AutocompleteService()
+        let text = "hi @al there"
+
+        let result = service.getSuggestions(
+            for: text,
+            peers: ["alice", "albert"],
+            cursorPosition: text.count
+        )
+
+        #expect(result.suggestions.isEmpty)
+        #expect(result.range == nil)
+    }
+
+    @Test("Applying suggestions replaces the range and adds command spacing only when needed")
+    func applySuggestionReplacesRangeAndHandlesCommandSpacing() {
+        let service = AutocompleteService()
+
+        let mentionResult = service.applySuggestion("@alice", to: "hi @al", range: NSRange(location: 3, length: 3))
+        let msgCommand = service.applySuggestion("/msg", to: "/m", range: NSRange(location: 0, length: 2))
+        let clearCommand = service.applySuggestion("/clear", to: "/c", range: NSRange(location: 0, length: 2))
+
+        #expect(mentionResult == "hi @alice")
+        #expect(msgCommand == "/msg ")
+        #expect(clearCommand == "/clear")
+    }
+}