fix(richtext): don't markdown-detect cashu tokens

A cashuB token pasted into a chat rendered as raw base64 instead
of the redeem card, because the message was routed through the
markdown renderer rather than the rich-text renderer.

Root cause: computeIsMarkdown treats any content containing `__`
as markdown (bold). cashuB is base64url-encoded CBOR, and the
base64url alphabet uses `_`; a token whose CBOR ends with the
indefinite-length break marker (0xff) easily produces a trailing
run like `______`. The user's actual token did. The markdown
renderer has no CashuSegment support, so it just dumped the raw
text. The previous truncation patch was unrelated — the cutoff
guard already returned content.length for this 398-char token, so
truncation never fired.

Fix: when content contains `cashuA` or `cashuB` (case-insensitive),
short-circuit isMarkdown to false. The trade-off is that a chat
message mixing markdown formatting AND a cashu token will lose
the markdown rendering, but the cashu card showing up matters
more — and pure-markdown messages are unaffected.

Tests cover the exact user-reported token, the same token
embedded in a longer message, a synthetic cashuA, and a control
case proving plain `__bold__` is still classified as markdown.

amethyst/src/main/java/com/vitorpamplona/amethyst/service/CachedRichTextParser.kt

@@ -81,14 +81,28 @@ object CachedRichTextParser {
         return result
     }
 
-    private fun computeIsMarkdown(content: String): Boolean =
-        content.startsWith("> ") ||
+    private fun computeIsMarkdown(content: String): Boolean {
+        // Cashu v2/cashuB tokens are base64url payloads that routinely
+        // contain '__' (the base64url alphabet uses '_'; a token whose
+        // CBOR ends with a fixed-bytes break easily produces a tail
+        // like `______`). Without this exemption, the markdown detector
+        // tags any chat message carrying a cashuB token as markdown,
+        // the content is routed through RenderContentAsMarkdown, which
+        // has no knowledge of CashuSegment, and the user sees the raw
+        // base64 instead of the redeem card. cashuA (v3 JSON+base64url)
+        // shares the same alphabet and the same risk. Force the
+        // rich-text path whenever a cashu token is present so the
+        // inline CashuPreview renders.
+        if (content.contains("cashuA", true) || content.contains("cashuB", true)) return false
+
+        return content.startsWith("> ") ||
             content.startsWith("# ") ||
             content.contains("##") ||
             content.contains("__") ||
             content.contains("**") ||
             content.contains("```") ||
             content.contains("](")
+    }
 }
 
 object CachedUrlParser {

amethyst/src/test/java/com/vitorpamplona/amethyst/CachedRichTextParserMarkdownTest.kt

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst
+
+import com.vitorpamplona.amethyst.service.CachedRichTextParser
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class CachedRichTextParserMarkdownTest {
+    private val cashuBToken =
+        "cashuBv2FteCJodHRwczovL21pbnQubWluaWJpdHMuY2FzaC9CaXRjb2luYXVjc2F0YWRkVEVTVGF0n79haUgAEHk32wzI" +
+            "ZWFwn79hYQJhc3hAZWM1YWI3Yjc1NjViYjBjZTZhNzg2NzBkMDA0OGExMjVlZGQzMjJhYmVjMTEzYWMwZTBmZGVkZmE3NTQ4Mzg3OWFj" +
+            "WCED0-ops8Ta6NjKChNJPe_jgIbXLlyxg2KSy2WaSTADo5D_v2FhCGFzeEBkNDZlODU5MDExNjU0NmNjZjAwNTE3ZTQ1NmU0MTY0N2Fm" +
+            "ZWUxOWNlMzY2N2IzYTcxODZkMzEwZDY1MjM3OTM4YWNYIQMTDGTY943O4ojhKopoYdemsUE2rSLfzwNBODL8WgOX0v______"
+
+    @Test
+    fun cashuBTokenWithTrailingUnderscoresIsNotMarkdown() {
+        // Bug repro: the user's token tail is `______`, which the
+        // markdown detector tagged as bold via the `contains("__")`
+        // check. RenderContentAsMarkdown has no CashuSegment support,
+        // so the chat bubble rendered the raw base64 instead of the
+        // redeem card. The exemption forces the rich-text path.
+        assertFalse(CachedRichTextParser.isMarkdown(cashuBToken))
+    }
+
+    @Test
+    fun cashuBTokenInLongerMessageIsNotMarkdown() {
+        val text = "Here, send to a friend: $cashuBToken"
+        assertFalse(CachedRichTextParser.isMarkdown(text))
+    }
+
+    @Test
+    fun cashuATokenIsNotMarkdown() {
+        // cashuA payloads share the base64url alphabet, so the same
+        // false-positive risk applies. Pre-empt it.
+        val fakeCashuA = "cashuAeyJ0b2tlbiI6W3sicHJvb2ZzIjpbXX1dfQ___"
+        assertFalse(CachedRichTextParser.isMarkdown(fakeCashuA))
+    }
+
+    @Test
+    fun plainBoldStillRecognizedAsMarkdown() {
+        // Make sure the exemption is targeted — content without a cashu
+        // prefix still triggers the markdown branch.
+        assertTrue(CachedRichTextParser.isMarkdown("hello __world__"))
+    }
+}

amethyst/src/test/java/com/vitorpamplona/amethyst/CashuV4ParserTest.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst
+
+import com.vitorpamplona.amethyst.service.cashu.v4.V4Parser
+import com.vitorpamplona.amethyst.ui.components.GenericLoadable
+import org.junit.Assert.assertTrue
+import org.junit.Assert.fail
+import org.junit.Test
+
+class CashuV4ParserTest {
+    @Test
+    fun decodesMinibitsTestToken() {
+        val token =
+            "cashuBv2FteCJodHRwczovL21pbnQubWluaWJpdHMuY2FzaC9CaXRjb2luYXVjc2F0YWRkVEVTVGF0n79haUgAEHk32wzI" +
+                "ZWFwn79hYQJhc3hAZWM1YWI3Yjc1NjViYjBjZTZhNzg2NzBkMDA0OGExMjVlZGQzMjJhYmVjMTEzYWMwZTBmZGVkZmE3NTQ4Mzg3OWFj" +
+                "WCED0-ops8Ta6NjKChNJPe_jgIbXLlyxg2KSy2WaSTADo5D_v2FhCGFzeEBkNDZlODU5MDExNjU0NmNjZjAwNTE3ZTQ1NmU0MTY0N2Fm" +
+                "ZWUxOWNlMzY2N2IzYTcxODZkMzEwZDY1MjM3OTM4YWNYIQMTDGTY943O4ojhKopoYdemsUE2rSLfzwNBODL8WgOX0v______"
+
+        val outcome = V4Parser.parseCashuB(token)
+        when (outcome) {
+            is GenericLoadable.Loaded -> {
+                val list = outcome.loaded
+                assertTrue("Expected at least one CashuToken", list.isNotEmpty())
+                val first = list.first()
+                println("mint=${first.mint} totalAmount=${first.totalAmount} proofs=${first.proofs.size}")
+            }
+            is GenericLoadable.Error -> fail("V4Parser failed: ${outcome.errorMessage}")
+            else -> fail("V4Parser returned $outcome")
+        }
+    }
+}