fix(telegram): add MarkdownV2 support for strikethrough, spoiler, and blockquotes

- Convert ~~text~~ to ~text~ (MarkdownV2 strikethrough)
- Protect ||text|| from pipe escaping (MarkdownV2 spoiler)
- Preserve > at line start as blockquote instead of escaping it
- Update _strip_mdv2() to strip ~strikethrough~ and ||spoiler|| markers
- Add tests covering new formatting paths and edge cases

tests/gateway/test_telegram_format.py

@@ -295,6 +295,95 @@ class TestItalicNewlineBug:
         assert "_italic_" in result
 
 
+# =========================================================================
+# format_message - strikethrough
+# =========================================================================
+
+
+class TestFormatMessageStrikethrough:
+    def test_strikethrough_converted(self, adapter):
+        result = adapter.format_message("This is ~~deleted~~ text")
+        assert "~deleted~" in result
+        assert "~~" not in result
+
+    def test_strikethrough_with_special_chars(self, adapter):
+        result = adapter.format_message("~~hello.world!~~")
+        assert "~hello\\.world\\!~" in result
+
+    def test_strikethrough_in_code_not_converted(self, adapter):
+        result = adapter.format_message("`~~not struck~~`")
+        assert "`~~not struck~~`" in result
+
+    def test_strikethrough_with_bold(self, adapter):
+        result = adapter.format_message("**bold** and ~~struck~~")
+        assert "*bold*" in result
+        assert "~struck~" in result
+
+
+# =========================================================================
+# format_message - spoiler
+# =========================================================================
+
+
+class TestFormatMessageSpoiler:
+    def test_spoiler_converted(self, adapter):
+        result = adapter.format_message("This is ||hidden|| text")
+        assert "||hidden||" in result
+
+    def test_spoiler_with_special_chars(self, adapter):
+        result = adapter.format_message("||hello.world!||")
+        assert "||hello\\.world\\!||" in result
+
+    def test_spoiler_in_code_not_converted(self, adapter):
+        result = adapter.format_message("`||not spoiler||`")
+        assert "`||not spoiler||`" in result
+
+    def test_spoiler_pipes_not_escaped(self, adapter):
+        """The || delimiters must not be escaped as \\|\\|."""
+        result = adapter.format_message("||secret||")
+        assert "\\|\\|" not in result
+        assert "||secret||" in result
+
+
+# =========================================================================
+# format_message - blockquote
+# =========================================================================
+
+
+class TestFormatMessageBlockquote:
+    def test_blockquote_converted(self, adapter):
+        result = adapter.format_message("> This is a quote")
+        assert "> This is a quote" in result
+        # > must NOT be escaped
+        assert "\\>" not in result
+
+    def test_blockquote_with_special_chars(self, adapter):
+        result = adapter.format_message("> Hello (world)!")
+        assert "> Hello \\(world\\)\\!" in result
+        assert "\\>" not in result
+
+    def test_blockquote_multiline(self, adapter):
+        text = "> Line one\n> Line two"
+        result = adapter.format_message(text)
+        assert "> Line one" in result
+        assert "> Line two" in result
+        assert "\\>" not in result
+
+    def test_blockquote_in_code_not_converted(self, adapter):
+        result = adapter.format_message("```\n> not a quote\n```")
+        assert "> not a quote" in result
+
+    def test_nested_blockquote(self, adapter):
+        result = adapter.format_message(">> Nested quote")
+        assert ">> Nested quote" in result
+        assert "\\>" not in result
+
+    def test_gt_in_middle_of_line_still_escaped(self, adapter):
+        """Only > at line start is a blockquote; mid-line > should be escaped."""
+        result = adapter.format_message("5 > 3")
+        assert "\\>" in result
+
+
 # =========================================================================
 # format_message - mixed/complex
 # =========================================================================
@@ -393,6 +482,12 @@ class TestStripMdv2:
     def test_empty_string(self):
         assert _strip_mdv2("") == ""
 
+    def test_removes_strikethrough_markers(self):
+        assert _strip_mdv2("~struck text~") == "struck text"
+
+    def test_removes_spoiler_markers(self):
+        assert _strip_mdv2("||hidden text||") == "hidden text"
+
 
 @pytest.mark.asyncio
 async def test_send_escapes_chunk_indicator_for_markdownv2(adapter):