mode_main() crashes with KeyError on invalid step number

[Alan-Chen99]

Description

skills/scripts/skills/lib/workflow/cli.py:116 crashes with unhandled KeyError: 'title' when workflow scripts are invoked with invalid step numbers.

Reproduction

python3 -m skills.planner.architect.plan_design_execute \
  --step 99 \
  --state-dir /tmp/test

Expected Behavior

Error message printed to stderr, exit code 1.

Actual Behavior

Traceback (most recent call last):
  File "skills/scripts/skills/lib/workflow/cli.py", line 116, in mode_main
    title=guidance_dict["title"],
KeyError: 'title'

Root Cause

When get_step_guidance() returns {"error": "Invalid step 99"}, mode_main() attempts to access guidance_dict["title"] without checking if the dict contains an error.

This affects all workflow scripts using mode_main() — approximately 22 functions across the planner skill return error dicts for invalid steps.

Environment

• Commit: 6e72bc2 (2026-02-16)
• File: skills/scripts/skills/lib/workflow/cli.py:116