fix: handle Forbidden when sending confirm-thread-creation DM (#3442)

Author: 13-Prabhat

CHANGELOG.md

@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 This project mostly adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html);
 however, insignificant breaking changes do not guarantee a major version bump, see the reasoning [here](https://github.com/modmail-dev/modmail/issues/319). If you're a plugin developer, note the "BREAKING" section.
 
+# Unreleased
+
+### Fixed
+* Confirm thread creation (react to contact) no longer leaves a thread stuck in a "not ready" cache state when the recipient has DMs disabled. The bot now catches `discord.Forbidden` when sending the confirmation prompt, cancels the thread, and clears the cache entry immediately instead of requiring a bot restart. (#3442)
+
 # v4.2.1
 
 ### Added

core/thread.py

@@ -2664,14 +2664,27 @@ async def create(
                     self.bot.config["confirm_thread_creation_deny"],
                 )
             )
-            confirm = await destination.send(
-                embed=discord.Embed(
-                    title=self.bot.config["confirm_thread_creation_title"],
-                    description=self.bot.config["confirm_thread_response"],
-                    color=self.bot.main_color,
-                ),
-                view=view,
-            )
+            try:
+                confirm = await destination.send(
+                    embed=discord.Embed(
+                        title=self.bot.config["confirm_thread_creation_title"],
+                        description=self.bot.config["confirm_thread_response"],
+                        color=self.bot.main_color,
+                    ),
+                    view=view,
+                )
+            except discord.Forbidden:
+                # Recipient has DMs disabled (or otherwise unreachable). Without this,
+                # the thread would stay stuck in cache in a "not ready" state until a
+                # bot restart, since view.wait() below would never run.
+                logger.warning(
+                    "Could not send confirm-thread-creation message to %s, DMs are likely disabled.",
+                    recipient,
+                )
+                thread.cancelled = True
+                del self.cache[recipient.id]
+                return thread
+
             await view.wait()
             if view.value is None:
                 thread.cancelled = True