Five narrow cases where a custom portal is justified: unmodeled workflow / proprietary integration / portal-is-the-product / data-residency / scale-inversion

Synthesis: A custom portal is justified ONLY in these narrow cases:

1. A core workflow no SaaS models — the business does something specific that off-the-shelf platforms cannot represent.
2. Deep integration with proprietary systems / data — when the portal must speak to bespoke internal systems the SaaS providers can't reach.
3. The portal IS the differentiated product / service — when client-facing analytics or capability is the value being sold (not back-office plumbing).
4. Data-residency / custody requirements a SaaS can't meet — regulated context where the vendor stack does not satisfy the rules.
5. Scale where per-seat SaaS pricing inverts vs a flat-cost owned system — usually hundreds-to-thousands of seats.

Source: Synthesis from oski.site ; digiteum.com ; strategeonsoftwares.com

Confidence: Directional-Speculative / Industry-consensus.

Why this matters for Candid: Operationalises R1 — Default to BUY, not build, for client portals; recommend a horizontal platform ($19-79/mo) or the bundled vertical-SaaS portal. If none of these five conditions hold, buying is the right answer — full stop.