feat(fase1): spike A - group chat maker-checker vs single-agent [skip-docs]

docs/fase1-spikes/findings-a.md

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+# Spike A findings — Group Chat maker-checker vs single-agent (U3 / G7)
+
+**Assumption (U3 / G7):** a Group Chat maker-checker debate (proposer · critic ·
+validator) beats a single-agent baseline by enough to justify its *multiplicative*
+token cost.
+
+## Verdict logic (proven by the quality gate — always green)
+
+The falsifiable decision lives in `spikes/a_groupchat.py::verdict(mc, single)`:
+
+- **better** = maker-checker caught the planted flaw AND the single agent did not.
+- **affordable** = maker-checker tokens ≤ **3×** the single-agent tokens (G7 discipline).
+- **passed** = better AND affordable.
+
+`tests/spikes/test_a_groupchat.py` exercises this with *varied* inputs (non-tautological):
+passes when better & within 3×; fails when better but 5× (unaffordable); fails when both
+caught the flaw (not better). `make_termination(3)` stops at 3 rounds. **Result: logic
+layer CONFIRMED green.**
+
+## Builder de-risk (from Step 2)
+
+The Step 2 builder smoke confirmed `FakeChatClient` can drive the GA `GroupChatBuilder`
+(`selection_func` + `with_max_rounds`) — so the maker-checker arm is buildable. The round
+cap terminates reliably ("reached max_rounds=N; forcing completion").
+
+## Token use
+
+The **empirical** better/cheaper numbers (convergence rounds, stall frequency, token use
+for BOTH arms) are produced by the gated `run_live` arm, which counts tokens as a
+word-count proxy over assistant outputs. They are **endpoint-dependent**: only measured
+when a LOCAL OpenAI-compatible endpoint is configured (`PORTFOLIO_LOCAL_BASE_URL` +
+`PORTFOLIO_LOCAL_MODEL`).
+
+- **Live arm token use this session:** _not run — no LOCAL endpoint configured._ The
+  logic layer (verdict function) is what the quality gate proves; the cheaper/better
+  verdict is honestly reported as endpoint-dependent and will be filled in by `run_live`
+  when an endpoint is available.
+
+## Implication for Fase 2
+
+The maker-checker machinery is buildable and its cheaper/better decision is codified and
+tested. Whether the debate is *worth its cost* on real models is the one open empirical
+question — to be measured with a LOCAL endpoint before committing the debate default in
+the Fase 2 vertical slice.