[FEATURE] Context threshold hooks to auto-trigger skills (e.g., session handoff at 70%)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Problem

When working on complex, multi-step tasks, sessions often hit context limits unexpectedly. By the time the user or Claude notices, it's too late to create a proper handoff document - work context is
lost and the next session starts from scratch.

Currently there is no way to automatically trigger a skill based on context window utilization. Claude has no self-awareness of its token usage during a session, and the hook system only supports
tool-based events (PreToolUse, PostToolUse), not context-based events.

Proposed Solution

Add a context threshold event system that can trigger skills or hooks at configurable utilization percentages.

Example configuration in .claude/settings.json:

{
"contextThresholds": [
{
"percentage": 70,
"action": "skill",
"skill": "session-handoff-skill"
},
{
"percentage": 90,
"action": "notification",
"message": "Context limit approaching - consider wrapping up"
}
]
}

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

Use Cases

• Session handoff: Auto-trigger handoff document creation at 70% to preserve work context before limits hit
• User notification: Warn the user at configurable thresholds so they can prioritize remaining work
• Checkpoint creation: Periodically save progress on long-running tasks
• Multi-session planning: Automatically break remaining work into follow-up tasks

Current Workarounds

• Adding heuristic instructions to CLAUDE.md ("proactively create handoffs during long sessions") - unreliable since Claude can't measure actual token usage
• Manually invoking /session-handoff-skill - requires user to guess when context is getting full
• Using multi-session-planner upfront - helps but doesn't cover sessions that unexpectedly grow large

Additional Context

_No response_