Include day of week in system prompt date

Problem

The system prompt includes the date in the <env> block:

Today's date: 2026-01-15

However, Claude sometimes gets the day of week wrong when reasoning about dates (e.g., saying "Wednesday 15th" when it's actually Thursday). This leads to errors in date-sensitive tasks like journaling.

Proposed Solution

Include the day of week in the date:

Today's date: Thursday, 2026-01-15

Or even more human-readable:

Today is Thursday, January 15, 2026

Workaround

Currently using a UserPromptSubmit hook to inject the day:

{
  "hooks": {
    "UserPromptSubmit": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "echo \"Today is $(date '+%A, %d %B %Y')\""
          }
        ]
      }
    ]
  }
}

This works but should be unnecessary - the system should provide unambiguous date context.