False 'user opened file' system reminders from IDE integration

Bug Description

When using Claude Code with VS Code, <system-reminder> tags are injected into the conversation claiming the user opened specific files in the IDE, even when those files are not open in any editor tab.

Examples observed in a single session:

1. The user opened the file /home/.../console/src/components/admin/ai/ChatInterface.tsx in the IDE — file was not open, and is in a completely different project than the working directory
2. The user opened the file /home/.../mcp-server/plugins/jobtread/src/services/job-service.ts in the IDE — file was not open; Claude had just read it via a tool call

Impact

• Claude acts on false context (e.g., reading files from wrong projects, making incorrect assumptions about user intent)
• Wastes user time correcting Claude's assumptions
• Erodes trust in the IDE integration signals

Expected Behavior

System reminders about opened files should only fire when the user actually opens or focuses a file tab in the IDE.

Environment

• Claude Code CLI with VS Code integration
• Linux (Ubuntu-based), VS Code
• Claude Opus 4.5