Claude should proactively warn users before context window fills up

Problem

When working on long, multi-step tasks, Claude can exhaust the context window (200k tokens) without ever warning the user. The user only discovers the problem when /compact fails and no further work can be done. This wastes both the user's time and their token budget.

Current behavior

• Claude works through tasks consuming tokens with no awareness of remaining context
• At 97%+ usage, /compact fails with "Conversation too long"
• The user is forced to start a new conversation, losing momentum and having to re-establish context
• No warning is given at 50%, 75%, 90%, or any threshold

Expected behavior

• Claude should monitor context usage and proactively warn the user at reasonable thresholds (e.g., 75%, 90%)
• At ~80%, Claude should suggest compacting or summarizing before it's too late
• At ~90%, Claude should stop taking on new tasks and recommend starting a fresh session
• The warning should be automatic — users shouldn't have to manually run /context to discover they're running low

Impact

• Wasted user time (work in progress is lost)
• Wasted tokens/money (the last chunk of work may need to be redone in a new session)
• Poor user experience — feels like the tool is working against you rather than for you

Environment

• Claude Code CLI
• Model: claude-opus-4-6
• Context limit: 200k tokens