diff --git a/src/shared/__init__.py b/src/shared/__init__.py
new file mode 100644
index 0000000..ad5da11
--- /dev/null
+++ b/src/shared/__init__.py
@@ -0,0 +1 @@
+# shared package
diff --git a/src/shared/patterns.py b/src/shared/patterns.py
new file mode 100644
index 0000000..9fbdc47
--- /dev/null
+++ b/src/shared/patterns.py
@@ -0,0 +1,28 @@
+"""
+Shared regex patterns used by both grok_bridge.py and grok_agent.py.
+
+Centralizing these patterns ensures consistent parsing across all modules.
+"""
+
+# Canonical list of supported file extensions for filename detection.
+SUPPORTED_EXTENSIONS = (
+    "py|js|ts|jsx|tsx|go|rs|java|c|cpp|h|hpp|cs|rb|php|swift|kt|scala|sh|bash"
+)
+
+# Regex pattern string that matches a comment-style filename header, e.g.:
+#   # filename.py
+_FILENAME_PATTERN_STRING = (
+    r"^\s*#\s*([a-zA-Z_][a-zA-Z0-9_]*\.(?:"
+    + SUPPORTED_EXTENSIONS
+    + r"))\s*$"
+)
+
+
+def get_filename_pattern_string() -> str:
+    """Return the canonical regex string for matching comment-style filename headers.
+
+    Both grok_bridge.py and grok_agent.py compile this string (with re.MULTILINE)
+    so that any change to the supported extension list is automatically reflected
+    in every consumer.
+    """
+    return _FILENAME_PATTERN_STRING