Closes the residual left open by the previous commit for gateway-ready
installs (#113017 review). _get_backend() and check_firecrawl_api_key()
already use read_selection semantics, but _get_firecrawl_client() still
keyed its "stored vendor selection: direct only" branch on
selection_exists("web"), which is true for a lone per-capability key. So
with only web.extract_backend set and the Nous Tool Gateway ready (no
FIRECRAWL keys), the search ladder resolved to firecrawl via the managed
slot and the client then refused it with a misleading "web is configured
to use firecrawl (set via hermes tools)" error — the other capability
still lost its normal cascade.
The direct-only branch is now keyed on an explicit firecrawl selection
(shared web.backend via read_selection, or a per-capability key that names
firecrawl via _is_explicit_firecrawl_selection). A per-capability key
naming another vendor is not a firecrawl selection, so a ladder-derived
firecrawl resolves exactly like a never-configured install: direct when
credentials exist, else managed. Explicit firecrawl selections keep their
direct-only (keyless-unlocking) behaviour; "nous" is untouched.
Test: test_ladder_derived_firecrawl_takes_managed_path_on_gateway_ready_install
— red on the previous commit (ValueError), green with this change.
816cb37963