fix: preserve literal markdown on renderer fallback

app/src/main/java/space/hackenslacker/kanbn4droid/app/carddetail/MarkdownRenderer.kt

@@ -20,7 +20,7 @@ class MarkdownRenderer(
             val html = parseToHtml(markdown)
             htmlToSpanned(html)
         } catch (_: Exception) {
-            htmlToSpanned(markdown)
+            PlainTextSpanned(markdown)
         }
     }
 
@@ -51,3 +51,31 @@ class MarkdownRenderer(
         }
     }
 }
+
+private class PlainTextSpanned(
+    private val text: String,
+) : Spanned {
+    override val length: Int
+        get() = text.length
+
+    override fun get(index: Int): Char = text[index]
+
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence {
+        return text.subSequence(startIndex, endIndex)
+    }
+
+    override fun toString(): String = text
+
+    override fun getSpanStart(tag: Any): Int = -1
+
+    override fun getSpanEnd(tag: Any): Int = -1
+
+    override fun getSpanFlags(tag: Any): Int = 0
+
+    override fun nextSpanTransition(start: Int, limit: Int, kind: Class<*>?): Int = limit
+
+    override fun <T : Any> getSpans(start: Int, end: Int, kind: Class<T>): Array<T> {
+        @Suppress("UNCHECKED_CAST")
+        return java.lang.reflect.Array.newInstance(kind, 0) as Array<T>
+    }
+}

app/src/test/java/space/hackenslacker/kanbn4droid/app/carddetail/MarkdownRendererTest.kt

@@ -34,7 +34,7 @@ class MarkdownRendererTest {
     fun render_whenRenderingFails_returnsPlainTextFallback() {
         val renderer = MarkdownRenderer(
             parseToHtml = { throw IllegalStateException("boom") },
-            htmlToSpanned = { html -> TestSpanned(html) },
+            htmlToSpanned = { throw AssertionError("htmlToSpanned should not run on fallback") },
         )
 
         val result = renderer.render("**keep this literal**")