The route inventory allow-listed every `.fallback_service` inside
`router::build_router`, and did not scan `.fallback` at all, so a new
sub-router fallback could add an unclassified handler without changing
the inventory. Allow-list entries now name the builder, call, and exact
whitespace-normalized argument, and each may appear once. The existing
buzz_v1 404 fallback is allow-listed explicitly.
`builder_prefixes` kept one prefix per builder, so nesting a builder at
a second prefix silently overwrote the first. A repeated nest is now a
hard error.
Five new fixtures cover a non-SPA fallback service, a repeated SPA
fallback, a handler fallback inside and outside build_router, and a
builder nested twice. All five fail against the previous scanner.
Co-authored-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Luke Tornquist <tornquist@squareup.com>
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