CLAUDE: Fix critical bug preventing Monday freeze/thaw from executing

## Problem
The weekly freeze/thaw system had a state flag initialization bug that prevented
both Monday freeze operations and Saturday thaw operations from executing.

## Root Cause (Introduced in commit 07f69eb on Oct 25, 2025)
The `weekly_warning_sent` boolean flag was being used for TWO different purposes:
1. Preventing duplicate freeze/thaw operations (state machine)
2. Preventing duplicate error notifications

The flag was initialized to `False`, but the Monday freeze condition required
it to be `True`:
- Line 205: `if ... and self.weekly_warning_sent:` (required True)
- Line 160: `self.weekly_warning_sent = False` (initialized to False)

This created a deadlock:
- Monday freeze: Never ran (flag was False, needed True)
- Saturday thaw: Never ran (freeze flag in DB never set to True)

## Impact
- First failure: Monday October 27, 2025
- Affected weeks: 2+ weeks of missed freeze/thaw operations
- Result: Week did NOT increment, transactions did NOT execute

## Solution
Separated the two concerns and replaced boolean flag with week tracking:

1. **Deduplication**: Track `last_freeze_week` and `last_thaw_week` (int | None)
   - Monday: Execute if `last_freeze_week != current.week`
   - Saturday: Execute if `last_thaw_week != current.week`
   - Prevents duplicate operations during same hour (loop runs every minute)

2. **Error notifications**: Separate `error_notification_sent` boolean flag
   - Only used for preventing duplicate error notifications
   - Clear separation of concerns

## Validation
Created and ran validation script simulating 7 scenarios across multiple weeks:
- ✅ Monday freeze executes on first check
- ✅ Monday freeze skips on subsequent checks same hour
- ✅ Saturday thaw executes on first check
- ✅ Saturday thaw skips on subsequent checks same hour
- ✅ Next Monday freeze executes for new week
- ✅ Week numbers increment correctly (19→20→21→22)
- ✅ All state transitions work as expected

## Files Changed
- tasks/transaction_freeze.py:157-167 - Separated state tracking from error flags
- tasks/transaction_freeze.py:211-231 - Fixed freeze/thaw conditions with week tracking
- tasks/transaction_freeze.py:248-250 - Updated error notification flag name

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tasks/transaction_freeze.py

@@ -157,7 +157,14 @@ class TransactionFreezeTask:
     def __init__(self, bot: commands.Bot):
         self.bot = bot
         self.logger = get_contextual_logger(f'{__name__}.TransactionFreezeTask')
-        self.weekly_warning_sent = False  # Prevent duplicate error notifications
+
+        # Track last execution to prevent duplicate operations
+        self.last_freeze_week: int | None = None
+        self.last_thaw_week: int | None = None
+
+        # Track error notifications separately
+        self.error_notification_sent = False
+
         self.logger.info("Transaction freeze/thaw task initialized")
 
         # Start the weekly loop
@@ -202,16 +209,27 @@ class TransactionFreezeTask:
             )
 
             # BEGIN FREEZE: Monday at 00:00, not already frozen
-            if now.weekday() == 0 and now.hour == 0 and not current.freeze and self.weekly_warning_sent:
-                self.logger.info("Triggering freeze begin")
+            if now.weekday() == 0 and now.hour == 0 and not current.freeze:
+                # Only run if we haven't already frozen this week
+                # Track the week we're freezing FROM (before increment)
+                if self.last_freeze_week != current.week:
+                    self.logger.info("Triggering freeze begin", current_week=current.week)
                     await self._begin_freeze(current)
-                self.weekly_warning_sent = False
+                    self.last_freeze_week = current.week  # Track the week we froze (before increment)
+                    self.error_notification_sent = False  # Reset error flag for new cycle
+                else:
+                    self.logger.debug("Freeze already executed for week", week=current.week)
 
             # END FREEZE: Saturday at 00:00, currently frozen
-            elif now.weekday() == 5 and now.hour == 0 and current.freeze and not self.weekly_warning_sent:
-                self.logger.info("Triggering freeze end")
+            elif now.weekday() == 5 and now.hour == 0 and current.freeze:
+                # Only run if we haven't already thawed this week
+                if self.last_thaw_week != current.week:
+                    self.logger.info("Triggering freeze end", current_week=current.week)
                     await self._end_freeze(current)
-                self.weekly_warning_sent = True
+                    self.last_thaw_week = current.week
+                    self.error_notification_sent = False  # Reset error flag for new cycle
+                else:
+                    self.logger.debug("Thaw already executed for week", week=current.week)
 
             else:
                 self.logger.debug("No freeze/thaw action needed at this time")
@@ -228,9 +246,9 @@ class TransactionFreezeTask:
             )
 
             try:
-                if not self.weekly_warning_sent:
+                if not self.error_notification_sent:
                     await self._send_owner_notification(error_message)
-                    self.weekly_warning_sent = True
+                    self.error_notification_sent = True
             except Exception as notify_error:
                 self.logger.error(f"Failed to send error notification: {notify_error}")