/goal Stop hook fails with "Prompt is too long" when goal text is large #58192

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Setting a long goal via /goal installs a session-scoped Stop hook whose condition is the entire goal text verbatim. On every Stop, the hook evaluator
re-sends that text to the model. If the goal is long enough, the evaluator rejects it with:

Hook evaluator API error: Prompt is too long

Once this state is reached, the turn cannot Stop cleanly until the goal is cleared.

What Should Happen?

Either:

• /goal rejects or truncates input that would exceed the Stop-hook evaluator's prompt budget, with a clear message at set time; or
• The Stop-hook evaluator handles an oversized condition gracefully (skip, warn, or summarise) instead of blocking Stop.

The Stop hook should never become unable to evaluate itself because the user provided a long goal.

Error Messages/Logs

Hook evaluator API error: Prompt is too long

Steps to Reproduce

1. Start a Claude Code session in any project.
2. Run /goal with a long multi-paragraph argument. A reliable repro is to paste ~30+ lines including file paths, a plan pointer, and a paragraph of constraints
   — for example:
   /goal Please work from this handoff plan:

/path/to/docs/superpowers/plans/<long-plan-name>.md

Repo path:

/path/to/repo

Goal: <several lines of overarching aim>

<several more lines of constraints, directives, "do not do X",
 "start with Task 1 then Task 2", etc.>

3. Work normally for a turn or two — text generation and tool calls all succeed.
4. Reach the end of a turn so that Stop fires.
5. The Stop hook errors with Hook evaluator API error: Prompt is too long and blocks the Stop. Subsequent Stops repeat the same error.

Workaround that recovers cleanly: /goal clear. After clearing, Stop works again. Short single-sentence goals do not trigger the bug.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

2.1.139

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

• The failure depends only on the length of the /goal argument, not on the project, the tools used, or the model's responses during the turn.
• Likely root cause: the Stop hook's evaluator prompt includes the literal goal-condition text on every Stop, so the evaluator's prompt grows proportionally to
  the goal length. Once the condition pushes the evaluator over its own context budget, every Stop fails identically.
• Suggested fix direction: either cap /goal argument length at set time with a friendly error, or have the Stop-hook evaluator fall back to a compact
  representation (hash + truncated preview) when the literal condition would exceed budget.