Documents the new architectural surface #1820 introduces, per the
contributor-standards ADR requirement (a new Module seam that other code
will depend on):
- The spec-section detection Module seam (src/spec-section.cts) and its
locked exported surface, supply rule, suffix-tolerant header invariant,
and ownership boundary (detection only).
- The workflow.specless_probe_fallback toggle as a policy decision
(default-on, disableable cost-gate over the fallback INVOCATION path, not
the verifier<->predicate contract) — records the maintainer 857:66 ruling
rather than amending it.
- The SPEC-supplied <-> probe-derived precedence & authoring contract:
section-level precedence (a SPEC-supplied section is never re-run), one
projectProhibitions serializer (no second producer), descriptor-less
fallback predicates flag/abstain (never green, never auto-dismissed),
no-silent-drop equality.
Does not restate ADR-857/550/1606; cross-references them. Resolves the
sole remaining review blocker on #1835.
Refs #1820
Claude-Session: https://claude.ai/code/session_017vYn26e3nkDNxcpty1ciPJ
