Add failing tests for #643: hard stop casing mismatch

[prompt-driven-github]

Summary

Adds failing tests that detect the bug reported in #643 — _check_hard_stop uses title-case string matching that doesn't match the lowercase STOP_CONDITION: format the prompts instruct the LLM to output.

Test Files

• Unit tests: tests/test_issue_643_hard_stop_casing.py
• E2E tests: tests/test_e2e_issue_643_hard_stop_casing.py

Prompt Files

• Step 4 prompt fixed in Step 5.5: pdd/prompts/agentic_change_step4_clarify_LLM.prompt (added missing STOP_CONDITION: marker)

What This PR Contains

• 6 failing unit tests that reproduce the casing mismatch in _check_hard_stop
• 4 failing E2E tests that verify the orchestrator continues past steps 4/7 with prompt-instructed output
• 4 passing regression tests confirming existing title-case detection still works
• Prompt fix adding STOP_CONDITION: Clarification needed to the step 4 prompt

Root Cause

_check_hard_stop() at pdd/agentic_change_orchestrator.py:319,323 checks for "Clarification Needed" and "Architectural Decision Needed" (title case), but the prompts instruct the LLM to output STOP_CONDITION: Clarification needed and STOP_CONDITION: Architectural decision needed (lowercase). The step 4 prompt was also missing the STOP_CONDITION marker entirely.

Next Steps

1. Make _check_hard_stop detect the STOP_CONDITION: prefix format with case-insensitive matching
2. Verify all unit tests pass
3. Verify all E2E tests pass
4. Run full test suite
5. Mark PR as ready for review

Fixes #643

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