feat: Add Gmail thread support and fix message ID vs thread ID confusion

- Add get_gmail_thread_content() function to retrieve complete conversation threads
- Enhance search_gmail_messages() to display both Message ID and Thread ID clearly
- Add helper function _extract_message_body() for consistent message parsing
- Fix 404 errors caused by using message IDs with thread functions
- Include usage guidance to prevent confusion between message and thread operations
- Add comprehensive documentation for both features

Resolves issue where users couldn't distinguish between message IDs and thread IDs,
leading to API errors when trying to retrieve thread content.

GMAIL_MESSAGE_THREAD_ID_FIX.md

@@ -0,0 +1,109 @@
+# Gmail Message ID vs Thread ID Fix
+
+## ✅ Implementation Complete
+
+Successfully enhanced the `search_gmail_messages` function to clearly distinguish between Message IDs and Thread IDs, eliminating the confusion that caused 404 errors when users tried to use message IDs with thread functions.
+
+## 🔧 Changes Made
+
+### Enhanced `search_gmail_messages` Output
+
+**Before:**
+```
+Found 3 messages:
+- ID: 196fd200c3c45ccb
+- ID: 196fd201c3c45ccd  
+- ID: 196fd202c3c45cce
+```
+
+**After:**
+```
+Found 3 messages:
+
+Note: Use Message ID with get_gmail_message_content, Thread ID with get_gmail_thread_content
+
+1. Message ID: 196fd200c3c45ccb
+   Thread ID:  196fd1b6256512d0
+
+2. Message ID: 196fd201c3c45ccd
+   Thread ID:  196fd1b6256512d0
+
+3. Message ID: 196fd202c3c45cce
+   Thread ID:  196fd1b6256512d0
+```
+
+### Code Changes
+
+1. **Enhanced Output Formatting** (lines 156-175)
+   - Added clear usage guidance note
+   - Display both Message ID and Thread ID for each message
+   - Numbered list format for better readability
+   - Proper spacing and alignment
+
+2. **Updated Function Documentation** (lines 80-93)
+   - Updated docstring to reflect new functionality
+   - Clarified that both Message IDs and Thread IDs are returned
+   - Added usage guidance in the return description
+
+## 🎯 Problem Solved
+
+### Root Cause
+- Gmail API `users.messages.list` returns both `id` (message ID) and `threadId` (thread ID)
+- Previous implementation only showed message IDs
+- Users tried to use message IDs with `get_gmail_thread_content` (which needs thread IDs)
+- This caused 404 errors because message IDs ≠ thread IDs
+
+### Solution Benefits
+- ✅ **Eliminates confusion** - Clear labeling of Message ID vs Thread ID
+- ✅ **Prevents 404 errors** - Users know which ID to use with which function
+- ✅ **Educational** - Helps users understand Gmail's message/thread relationship
+- ✅ **Flexible** - Users can choose message-level or thread-level operations
+- ✅ **Backward compatible** - Doesn't break existing functionality
+- ✅ **Follows codebase style** - Maintains consistent formatting and patterns
+
+## 📋 Usage Guide
+
+### For Individual Messages
+```
+get_gmail_message_content(message_id="196fd200c3c45ccb")
+```
+
+### For Complete Conversation Threads
+```
+get_gmail_thread_content(thread_id="196fd1b6256512d0")
+```
+
+### Understanding the Relationship
+- **Multiple messages** can belong to the **same thread** (conversation)
+- **Message ID** = Individual email message
+- **Thread ID** = Entire conversation (multiple messages)
+
+## 🔍 Technical Details
+
+### Gmail API Response Structure
+The `users.messages.list` API already returns both fields:
+```json
+{
+  "messages": [
+    {
+      "id": "196fd200c3c45ccb",      // Message ID
+      "threadId": "196fd1b6256512d0"  // Thread ID
+    }
+  ]
+}
+```
+
+### Implementation Approach
+- Extract both `msg['id']` and `msg['threadId']` from API response
+- Format output with clear labeling and usage guidance
+- Maintain existing authentication and error handling patterns
+- Follow codebase style conventions
+
+## ✅ Testing
+
+- Code compiles without syntax errors
+- Function signature and parameters unchanged (backward compatible)
+- Enhanced output provides clear guidance for users
+- Follows existing codebase patterns and style
+
+The implementation successfully resolves the message ID vs thread ID confusion while maintaining the existing codebase style and functionality.