docs: MkDocs site with flow diagrams; RustFS permissions

Material for MkDocs site (mkdocs.yml, optional extra `docs`) with Mermaid via
the superfences custom fence. New pages: overview, scanning (modes, quick
rules, Joern engine, priors, pre-push delta), the plane on ax (one task as a
sequence, golden snapshot, Run DAGs), memory (row kinds, write/read paths,
FileStore vs S3, verify at startup), memory and detection, and RustFS setup
(admin steps, complete agent policy, .env, refusal messages, Select limit).
The ops READMEs are included at build time; evaluation gains the population
lifecycle and the fold layout. tests/test_docs_site.py runs the strict build
when mkdocs is importable and checks Mermaid blocks and the RustFS page.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

docs/evaluation.md

@@ -49,6 +49,43 @@ v3 is reserved: development and analysis work never reads its cases, and
 `tests/test_independent_population.py` fails when anything in the development tree (a recipe,
 catalog, manifest or measurement) names one of its repositories.
 
+```mermaid
+stateDiagram-v2
+    [*] --> Frozen: cases selected and frozen before any scan
+    Frozen --> Scored: scored once under the pre-registered protocol
+    Scored --> Spent: result recorded
+    Spent --> [*]: may inform changes, can no longer qualify anything
+    note right of Frozen
+        v3 (PHP, 15 cases) waits here as the one-time final check,
+        run once after a prediction is committed
+    end note
+    note right of Spent
+        v1 and v2 are spent
+    end note
+```
+
+## Folds: how learned decisions are kept out of their own training data
+
+The decision engine is evaluated on repositories it was not shown (`src/openultrasast/learn/folds.py`).
+Every split is by repository group (the label builder's normalised `owner/name`, merged across
+URLs, forks and shared advisories), across all corpora, seeded and deterministic.
+
+```mermaid
+flowchart TD
+    groups["All repository groups with labels"] --> c["Compile split: 25% of groups, never evaluated"]
+    groups --> rest["The other 75%"]
+    c --> boot["C_boot 60%: demonstrations"]
+    c --> val["C_val 40%: instruction scoring"]
+    rest --> outer["Outer grouped 5-fold: calibration cross-fitted, operating points nested"]
+    rest --> loso["Leave-one-source-out: a source held out whole"]
+    rest --> lofo["Leave-one-framework-out: frameworks with at least 10 groups"]
+```
+
+`assert_disjoint` runs before a compile: the compile split and the evaluation folds share no
+group. A framework with fewer than 10 groups gets `insufficient data` instead of a fold. As of
+2026-10-02 only the outer folds of the injection family have been run
+([decision-engine.md](decision-engine.md#first-measured-slice-2026-10-01)).
+
 ## The plane increment
 
 The first increment of the agentic plane ran the model-driven pipeline's validation set (46