docs(confidence-engine): checkpoint commercially testable product loop

docs/current-project-state.md

@@ -34,7 +34,13 @@ The product direction is a **facilitated investigation** presented across three
 
 **Report:** Renders persisted `investigationReport` snapshot. Generation is on-demand (exactly one `/api/cases/overview` call on first visit; zero on subsequent visits). The Report is a derived artefact, not canonical reasoning evidence.
 
-The user controls which question to investigate, when to say Done for now, whether Current Understanding is sufficient, whether to reopen work, and when to review the Report. The engine facilitates — it does not steer or prioritise.
+The user controls which question to investigate, how deeply to investigate it, when to say Done for now, whether Current Understanding is sufficient, whether to reopen work, and when to review the Report. The engine facilitates — it does not steer or prioritise.
+
+## September 8, 2026 Product Checkpoint
+
+`docs/confidence-engine-product-checkpoint-2026-09-08.md` is the current checkpoint for the established working loop, multi-turn supplier evidence, Done-for-now/Re-open graph-state behavior, persistence, provider position, measured Terra economics, and the move toward commercially testing realistic end-to-end use. It distinguishes proven observations from provisional cost extrapolation and known future questions.
+
+For the current stage, the primary question is increasingly whether this process leaves real people materially clearer about difficult situations, repeatedly enough that they will pay to use it. This does not weaken the invariant that the user owns investigation choice, depth, closure, reopening, sufficiency, confidence, and action; nor does it excuse trust-critical defects.
 
 ## 3. Current Engine Capabilities