M2 — Compute arbitrage decision tree

Eye-landing point

The root question at the top : souveraineté SecNumCloud livrable pédagogique du Master ? It is the actual fork in docs/compute/scenario-matrix.md §5.5, and it is the political question — not a technical one — that gates every downstream branch. The thick gold border on Q1 makes it the first thing the eye catches.

A reader scanning the diagram in three seconds should be able to answer : which architecture does the sovereignty branch resolve to? — answer : A4 (all-in S3NS, \(\approx\) €2 275 / an).

Layout discipline

• Root : Q1, the sovereignty question — gold border, drawn at top.
• Decision nodes : Q2 (hackathon scope) and Q3 (provider choice for the four recurring use cases). Three atomic atomic questions from scenario-matrix.md §5.5.
• Leaves : the five architecture leaves carry €/an cost and a one-line rationale. A4 is highlighted in red because it is the only leaf that survives the sovereignty fork.
• Branches : labelled with the human-readable answer that resolves the question (oui / non / crédit académique négocié / budget zéro).

What was deliberately excluded

• A1, A2, A3, A5, M4 — five architectures from the scenario matrix that are dominated transversally and are not viable defaults for any use case. Including them would dilute the fork.
• Per-UC cost breakdowns — the leaves carry a rolled-up annual cost across all five UCs. Per-UC cells live in scenario-matrix.md §4.
• Storage migration cost — captured in the migration 5,7 TiB requise tag on A4 only. The other leaves (M1/M2/M3/M5) preserve the storage-compute découplage so the migration cost is zero by construction.
• Egress projections — €/GB calculations belong to docs/compute/cost-model.md. Re-exposing them here would bloat the diagram into a spreadsheet.
• Friction / lock-in / latency — captured in the §4 matrix cells per UC. Re-flattening them into the tree would lose the per-UC granularity without adding decisional clarity.

Lint check (Obsidian-Mermaid pitfalls)

• [x] No <i> / <b> HTML tags inside labels (only <br/> line breaks).
• [x] No numbered prefixes 1. 2. at start of any label (Q1/Q2/Q3, A4, M1/M2/M3/M5 are dash-or-no-separator identifiers, not period lists).
• [x] No nested subgraph containing a single node — classDef is used for the four visual roles (rootQ, question, leafSov, leaf).

Render check

• GitHub Mermaid preview : OK.
• HTML wiki build pipeline : exercised by the sibling wiki-build pipeline.
• Banlist sweep on rendered SVG : passes (no internal-only vocabulary in node IDs, labels, or edge labels).