Reflection: Formatting is not business state

Trigger

An early Booking parser interpretation treated a yellow source row as cancellation. The supplied real workbook showed that a fully yellow row can still be the authoritative active Tour Code row, and the user confirmed that only explicit source cancellation text should cancel it.

Expected Behavior

The parser should derive replacement/cancellation from explicit business content and documented row order, not from presentation-only cell formatting.

Actual Behavior

A visual formatting heuristic could have removed a valid final Tour Code allocation.

Root Cause

Weak gate: a spreadsheet style was promoted to business meaning without an explicit contract or counterexample test.

Evidence

Files: booking_ingestion/excel.py, tests/test_booking_excel_ingestion.py
Command output: the supplied workbook retains its yellow final row; the regression test test_yellow_formatting_alone_does_not_cancel_a_tour passes.
Docs involved: .project-docs/40-domain/business-rules.md

Lesson

Spreadsheet color, font, border and other presentation metadata must remain non-authoritative unless the user explicitly defines that formatting as a business field. When row state matters, prefer text/column contracts and add a real-style counterexample before accepting the rule.

Action

Add check/eval: retain a yellow-row regression fixture and keep cancellation text-based.
Update docs: promote the rule to durable Booking business rules.

Promotion

Business rule plus parser regression test.

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