Mail (gmail) envelopes never get a document_summary (Decyzja 6 -- a mail
"summary" would usually be longer than the mail itself), so they're invisible
to the cascade's stage-1 pre-filter. hybrid_retrieve runs the existing
cascade for summarized sources (paperless) and, in parallel, a direct chunk
scan restricted to summaryless_sources (gmail), merging both by dist -- same
embedder/cosine space, so the merge is a plain sort, no re-normalization.
hybrid_query mirrors cascade_query (one shared query embed).
kb-query: mode pattern extended to ^(cascade|flat|hybrid)$, /search routes
"hybrid" to hybrid_query. Default mode stays "cascade" until the quality gate
(plan §8) PASSes on the full mail corpus -- flipping the default, and
deploying this to the running kb-query container, are separate follow-ups
for the operator; this task only adds the code path + tests
(docs/kb/modules/05-faza-mailowa-plan.md, §6, Krok 3).
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