Disconnected account-level MCP integrations still inject system-reminder noise into context

Bug description

When account-level MCP integrations (e.g., Gmail, Netlify) are disconnected via claude.ai Settings, Claude Code still attempts to connect to them on every turn. This results in repeated system-reminder injections into the conversation context:

1. A disconnect notice listing all unavailable tools (~200-400 tokens)
2. A reconnect notice when the connection is re-established, including full usage guidelines for services like Supabase (~500-800 tokens)

A full disconnect/reconnect cycle consumes 700-1200 tokens per turn in system-reminder overhead.

Impact

• Token waste: In conversations with short user messages (50-100 tokens), MCP system-reminders can exceed the actual conversation content by 10x
• Context pollution: These reminders occupy attention in the model's context window, potentially degrading response quality
• No user control: Built-in integrations like Gmail and Netlify can only be "disconnected", not "removed" from the account — so there's no way to stop Claude Code from repeatedly attempting to connect

Steps to reproduce

1. Go to claude.ai → Settings → Connected Apps
2. Disconnect an MCP integration (e.g., Gmail)
3. Start a Claude Code session (CLI)
4. Observe that system-reminders about MCP disconnect/reconnect are injected into the context on each turn

Expected behavior

• Disconnected integrations should not be attempted at all — no connection attempt, no system-reminder injection
• At minimum, a project-level opt-out (e.g., mcpDenyList in .claude/settings.json) would let users suppress specific account-level MCP servers

Additional context

• This is especially impactful for long-running Claude Code processes where the subprocess stays alive for hours — MCP HTTP connections time out and reconnect repeatedly
• Even after disconnecting Gmail/Netlify, the CLI still shows ‼ 2 setup issues: MCP on startup
• GitHub integration is also "not connected" but does NOT trigger these warnings, suggesting inconsistent handling

Environment

• Claude Code CLI (latest)
• Windows 11
• Account-level MCP integrations: Gmail, Netlify (disconnected), Supabase (connected)