[BUG] Hook loop silently burns all context tokens — session dies with no warning that a hook caused it

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported in this specific form
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

A custom PreToolUse hook entered a loop during an active agent session, firing on every tool invocation without completing cleanly. Each hook execution injects output as system-reminder context. The hook fired hundreds of times across a long session, silently consuming all available context tokens. The session died from context exhaustion.

The problem isn't just the death — it's the complete invisibility of the cause. The error shown to the user was the standard "context limit reached · /compact or /clear to continue." There was no indication that a hook was responsible. The user had no way to:

• Know a hook was looping
• See how many times it had fired
• Know how much context the hook had consumed
• Interrupt the hook before the session died

Hours of work were lost with no data recovery path.

Version

v2.1.92, Node.js runtime, Windows 11

Steps to Reproduce

1. Create a PreToolUse hook that reads state from a file and writes back to it (e.g., an audit/claims hook)
2. Run a complex multi-agent session with many tool invocations (100+ tool calls)
3. If the hook encounters a state management issue or logic error, it fires on every tool call
4. Context fills with hook output (each hook execution adds ~500-2000 tokens of system-reminder output)
5. After N invocations, context limit is reached
6. CC shows standard "context limit reached" — no mention of hooks

What Should Happen

At minimum, one of:

• Attribution in error message: "Context limit reached. Note: PreToolUse hook .claude/hooks/claims_hook.py fired 347 times this session, consuming approximately 180k tokens."
• Hook execution counter: Visible in /cost output or status line — "Hooks: 347 invocations, 183k tokens"
• Circuit breaker: When context > 85% full, pause hook execution and warn user: "Hook firing paused — context critically low. Hook .claude/hooks/X has fired 200+ times."
• Hook loop detection: If the same hook fires on >50 consecutive tool calls, warn: "Hook may be looping. Fire count: 50. Pause? [Y/N]"

Impact

• Complete session death with no recovery path
• Cause is invisible — user cannot diagnose why context filled so fast
• All in-progress work lost
• Particularly damaging for long-running agent sessions (overnight pipelines, multi-step analyses)

Related Issues

• #2038 — context loop / compaction spiral (oncall)
• #24179 — compaction death spiral (211 compactions)
• #35166 — MCP repeated requests loop ($500+ in tokens)

The pattern across all three: a runaway process silently consuming tokens with no user-visible warning until the session is already dead.

Proposed Fix Priority

Adding hook invocation counts to /cost output would take one engineer one day and prevent this entire class of invisible session deaths. Please prioritize this.

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Reproduced on v2.1.92, Windows 11, Node.js runtime. Max plan subscriber paying $200/month — currently doing Anthropic's QA testing for free.