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

docs/current-handoff.md

@@ -7,6 +7,8 @@
 
 Initial-decomposition hardening is frozen for the current MVP stage.
 
+**Current product checkpoint:** Read `docs/confidence-engine-product-checkpoint-2026-09-08.md` before planning new product, live-evidence, or commercial work. The core investigation loop is now sufficiently established to prioritise realistic end-to-end use, report experience, prospective-user value, repeat use, and willingness to pay—not endless isolated reasoning-mechanics experiments. Preserve user ownership and address trust-critical defects when found.
+
 Do not resume:
 - repeated-same-input reconstruction experiments
 - Qwen/Terra reconstruction comparison
@@ -17,15 +19,9 @@ Do not resume:
 
 unless new end-to-end user-flow evidence reopens one of those boundaries.
 
-**Immediate next evidence question:**
+**Immediate strategic evidence question:**
 
-Measure one real browser investigation configured for OpenAI/Terra across every LLM stage, including user-visible latency, call sequence, and cost.
-
-If YES, the next live experiment is one timed/costed OpenAI UI investigation measuring:
-- user-visible latency
-- OpenAI call count
-- token usage where available
-- approximate cost per investigation
+Does the complete investigation process leave real people materially clearer about genuinely difficult situations, repeatedly enough that they will pay to use it? Use measured realistic scenarios and bounded live action budgets; the September 8 checkpoint records the current Terra cost/latency evidence.
 
 ## Server-owned UI journey provider experiment
 
@@ -157,6 +153,7 @@ RAW USER EVIDENCE
 - If a prescribed semantic locator cannot find its control → STOP. No fallback to CSS/XPath/DOM traversal.
 - Live freeze: once Playwright verification begins, no production file edits until evidence is captured.
 - **Tests are instruments, not product truth.** At first deterministic failure: classify PRODUCT vs APPARATUS, then stop.
+- A failed prescribed UI step is evidence, not permission to explore: semantic `page.getByRole(...)` locators only; do not substitute actions, retry model-backed steps, or navigate away from a manually positioned persisted state. Define action budgets for live cost experiments.
 
 ## Current genuinely open boundaries
 
@@ -192,6 +189,7 @@ These results are documented as **historical experiment evidence**. The v0.61 li
 | Methodology / RTO axioms | `docs/current-working-principles.md` §0 (A1–A12) |
 | Architecture guardrails | `.claude/architecture-guardrails.md` |
 | Task routing by work type | `docs/task-context-packs.md` |
+| September 8 product/economics checkpoint | `docs/confidence-engine-product-checkpoint-2026-09-08.md` |
 | Full experiment history (specific) | `docs/design-evolution/README.md` → relevant chapter |
 
 Consult `docs/current-project-state.md` for broader project context and passive classifier status.