Claude skips EnterPlanMode despite tool description saying to use it proactively

Description

Claude consistently skips calling EnterPlanMode before implementing multi-file code changes, despite the tool's own description explicitly instructing proactive use.

EnterPlanMode tool description says:

Use this tool proactively when you're about to start a non-trivial implementation task.

And lists clear triggers:

• "Multi-File Changes: The task will likely touch more than 2-3 files"
• "New Feature Implementation: Adding meaningful new functionality"
• "Code Modifications: Changes that affect existing behavior or structure"
• "If unsure whether to use it, err on the side of planning"

Observed behavior

In a single conversation, Claude skipped plan mode twice for tasks that clearly matched the triggers:

1. "fix all of them" (repo audit fixes) -- edited 3 files (CLAUDE.md, README.md, marketplace.json) with ~30 individual edits. No plan mode entered.

1. "1 bug and 2 new features" (MD viewer app) -- edited 5 files (main.py, renderer.py, app.js, new CSS file, tests). Bug fix + edit mode feature + new theme. No plan mode entered.

Both tasks had multiple valid approaches and touched 3-5 files -- well above the tool's own "more than 2-3 files" threshold.

Expected behavior

Claude should call EnterPlanMode before starting implementation for any task matching the tool's trigger conditions, especially multi-file changes and new feature implementations.

Root cause hypothesis

The model appears to treat the EnterPlanMode tool description as informational rather than prescriptive. When a user's request feels immediately actionable (e.g., "fix all of them"), the model prioritizes executing over planning, even when the tool description explicitly says to plan first.

Environment

• Model: Claude Opus 4.6 (1M context) via AWS Bedrock
• Platform: Windows 11, Claude Code CLI
• The EnterPlanMode tool was available and loaded in the conversation

Reproduction

1. Open a Claude Code session with plan mode tools available
2. Ask Claude to fix multiple issues across several files, or implement a bug fix + features
3. Observe that Claude jumps straight to editing files without calling EnterPlanMode

Workaround

User can manually enter plan mode via /plan before giving the task, but this defeats the purpose of the tool's proactive usage instructions.