Fix heading with bold text producing malformed output (#11)

Both headings and bold map to `*` in Slack mrkdwn. When bold text
appears inside a heading, the nested `*` markers produce malformed
output like `**Step 1*: Description here*` instead of the correct
`*Step 1: Description here*`.

Suppress bold markers inside headings since the heading wrapper
already provides bold formatting, making nested bold redundant.

Fixes #10

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: thesmallstar

src/slackify_markdown/slackify.py

@@ -10,6 +10,8 @@
 # Todo: Clean code before release.
 class SlackifyMarkdown(RendererHTML):
 
+    _in_heading = False
+
     SUPPORTED_TOKENS = [
         "text",
         "inline",
@@ -112,6 +114,7 @@ def heading_open(
         options: Dict[str, Any],
         env: Dict[str, Any],
     ) -> str:
+        self.__class__._in_heading = True
         return "*"
 
     def heading_close(
@@ -121,6 +124,7 @@ def heading_close(
         options: Dict[str, Any],
         env: Dict[str, Any],
     ) -> str:
+        self.__class__._in_heading = False
         return "*\n\n"
 
     def strong_open(
@@ -130,6 +134,8 @@ def strong_open(
         options: Dict[str, Any],
         env: Dict[str, Any],
     ) -> str:
+        if self._in_heading:
+            return ""
         return "*"
 
     def strong_close(
@@ -139,6 +145,8 @@ def strong_close(
         options: Dict[str, Any],
         env: Dict[str, Any],
     ) -> str:
+        if self._in_heading:
+            return ""
         return "*"
 
     def em_open(

tests/test_convert.py

@@ -178,6 +178,12 @@ def test_headings():
     assert slackify_markdown(mrkdown) == slack
 
 
+def test_heading_with_bold():
+    assert slackify_markdown("### **Step 1**: Description here") == "*Step 1: Description here*\n\n"
+    assert slackify_markdown("### **Step 1**") == "*Step 1*\n\n"
+    assert slackify_markdown("# **Test**: text") == "*Test: text*\n\n"
+
+
 def test_bold():
     mrkdown = "**bold text**"
     slack = "*bold text*\n"