The user wants one Markdown note. The current facet is: Regional variation (SEC growth vs. northeast/rust belt decline). The final instruction: "Write one Markdown note: a single dated claim this Mind can stand behind. Start with a # title that is the claim in one line, then 1-3 short paragraphs. End with a line: What would change this: … Name a source for any load-bearing number or fact, or start that sentence with Unverified: Do not mention tools, searches, sessions, passes, or that you are writing a note. Do not invent evidence. If the session is only planning, output nothing."

Looking at the "Substance from this session" — there are many claims listed, but the current facet is "Regional variation (SEC growth vs. northeast/rust belt decline)". The most relevant durable claim on this facet is:

"Durable claim on the facet (regional variation, SEC growth vs. NE/Rust Belt decline): the bifurcation is the sum of three stacked currents all pointing one direction through ~2045 — (1) the demographic cliff falls hardest on the Northeast/Midwest, where the traditional college-age cohort shrinks fastest after 2026; (2) net domestic migration keeps relocating college-relevant households into the Sun Belt/SEC footprint (Texas, Florida, Georgia, Tennessee, the Carolinas), compounding the South's tax-base and enrollment advantage; (3) AI's first-mover disruption lands on white-collar task clusters concentrated in legacy Northeast/Rust Belt metros (finance, insurance, media, back-office services), collapsing the ROI of the high-tuition residential degree exactly where sticker prices are highest. Net effect: SEC-belt flagships and regional publics gain enrollment share, pricing power, and state capital; tuition-dependent small privates and non-flagship publics in the Northeast/Rust Belt shift from gradual attrition to accelerated closures and mergers. Crucially, flagship brands everywhere (Michigan, UVa, Wisconsin) are partially insulated — the shrinkage is region- AND stratum-specific, not a uniform national decline. This is the regional layer on top of the demand-shift mechanism already claimed."

That's the facet-specific claim. Other claims in the substance list belong to other facets (research function, PhD pipeline, enrollment demand shift, etc.), and there are already filed notes for those facets. The current facet is regional variation, so I should write the note on the three-stacked-currents claim.

Note there's also the "wind-down" claim: "Durable claim on the core question's regional resolution: AI-driven erosion of the generic bachelor's credential does not shrink US enrollment uniformly — it bifurcates demand geographically..." But that overlaps with Note 4 already filed ("AI bifurcates US university enrollment by region — 'grow or shrink' resolves as 'both'"). So the increment here is the three-stacked-currents decomposition plus the flagship-insulation point.

Also the instruction says "a single dated claim this Mind can stand behind." So one claim: the regional bifurcation is the sum of three stacked currents; shrinkage is region- and stratum-specific.

Load-bearing facts:
- Traditional college-age cohort shrinks fastest in Northeast/Midwest — supported by CDC/NCHS birth data (births fell ~17% from 4.32M in 2007 to 3.59M in 2023) and WICHE projections (HS grads peak ~2025 at ~3.9M/yr). These were cited in prior notes. I can name CDC/NCHS and WICHE.
- Net domestic migration to Sun Belt — Census Bureau data on domestic migration to TX, FL, GA, TN, Carolinas. That's real, I can name Census Bureau.
- AI disruption landing on white-collar task clusters in Northeast/Rust Belt metros — the occupation concentration (finance, insurance, media in NY/Boston/Chicago) is factually reasonable; the AI-exposure link is more speculative. The Stanford Digital Economy Lab "Canaries in the Coal Mine" (2025) found early-career declines in AI-exposed occupations — could cite for AI's impact on white-collar entry-level roles. That was already used in prior notes.

What would change this: If Sunbelt college-age cohorts don't grow as projected, or if migration reverses, or if AI-driven white-collar disruption hits Sunbelt metros equally (remote work decouples task location from degree location), or if flagship brands in the Northeast hold enrollment while SEC growth stalls — the stacked-currents picture weakens. Also: uniform national decline would falsify.

Format:
# Title — one line claim
1-3 short paragraphs
What would change this: …
Sources or Unverified: tags inline or at end.