1\begin{appendices}2\section{Source audit and compliance}\label{app:source}3The Phase~0 source audit (\texttt{reports/00\_source\_audit.md}) documents the three tables kept from the snapshot (\texttt{stores}, 4{,}082 rows; \texttt{products}, 465{,}388; \texttt{sync\_log}, 577{,}773), their fields, missingness and the platform's own compliance review per source: public catalogue endpoints only, polite rates, nothing behind authentication, retained attribution and removal on request. The research used no scraping of the platform and a single control request to its public statistics endpoint to date-stamp the counters.45\section{Data dictionary}\label{app:dictionary}6The full field-level dictionary of the cleaned tables (\texttt{listings\_clean}, \texttt{stores\_master}, \texttt{sibling\_stores}, \texttt{match\_pairs}, \texttt{match\_groups}, \texttt{sync\_log}) is generated by the pipeline (\texttt{reports/data\_dictionary.md}). Key derived fields: \texttt{title\_norm} (ASCII-folded, lower-cased title used for duplicate detection and matching); \texttt{f\_analysis\_assort} and \texttt{f\_analysis\_price} (sample membership flags); \texttt{region\_final} and \texttt{region\_source} (assigned region and its provenance: municipality lookup, platform label, FSA-centroid point-in-polygon, or unknown); \texttt{category\_model} (classifier label, Amendment A-002); \texttt{comparable} (variant-structure comparability of a matched pair).78\section{Category taxonomy and audit details}\label{app:categories}9\input{tables/category_audit}1011\section{Within-region concentration}\label{app:concentration}12\input{tables/h3_within_region}1314\section{Region-level indicators}\label{app:indicators}15\input{tables/h7_indicators}16\input{tables/qdaci}1718\section{Preregistration, decision log and amendments}\label{app:prereg}19The frozen preregistration (\texttt{research/preregistration.md}), the decision log (\texttt{research/decisions.md}, D-001 to D-007) and the two amendments are reproduced in the repository. A-001 (region assignment) replaced ``platform label first'' by ``official geography first'' after a first attempt with the Statistics Canada 2021 economic-region layer produced spurious Estrie/Montérégie conflicts that predate the 2021 boundary change; the final rule uses the MRNF municipality table for urban forward sortation areas, then the platform label, then the FSA-centroid point-in-polygon. A-002 (category labels) introduced a supervised classifier after the audit measured the keyword rules at 46\% precision, with the primacy rule stated before any result was computed under the new labels.20\end{appendices}21