app/api/cases/overview/route.js

@@ -6,7 +6,7 @@
  * Thin route pattern — no overview business logic here.
  */
 
-import { getProvider } from "@/lib/llm/provider.js";
+import { getProvider, getProviderModelName } from "@/lib/llm/provider.js";
 import { synthesizeInvestigationOverview } from "@/lib/graph/investigation-overview-synthesis.js";
 
 export async function POST(request) {
@@ -33,7 +33,7 @@ export async function POST(request) {
       { situationGraph, findings, plausibleInterpretations },
       {
         provider: getProvider(),
-        modelName: process.env.OLLAMA_MODEL ?? null,
+        modelName: getProviderModelName(),
       }
     );
 

app/api/cases/synthesis/route.js

@@ -9,7 +9,7 @@
  * No synthesis business logic belongs in this file.
  */
 
-import { getProvider } from "@/lib/llm/provider.js";
+import { getProvider, getProviderModelName } from "@/lib/llm/provider.js";
 import { synthesizeCurrentUnderstanding } from "@/lib/graph/current-understanding-synthesis.js";
 
 export async function POST(request) {
@@ -38,7 +38,7 @@ export async function POST(request) {
       { situationGraph, findings },
       {
         provider: getProvider(),
-        modelName: process.env.OLLAMA_MODEL ?? null,
+        modelName: getProviderModelName(),
       }
     );
 

app/api/focused-investigation/deconstruct/route.js

@@ -1,4 +1,4 @@
-import { getProvider } from "@/lib/llm/provider";
+import { getProvider, getProviderModelName } from "@/lib/llm/provider";
 import {
   buildFocusedDeconstructPrompt,
   focusedDeconstructJsonSchema,
@@ -58,7 +58,7 @@ export async function POST(request) {
     const startedAt = Date.now();
     const wrapper = await provider.generateReconstruction(
       prompt,
-      process.env.OLLAMA_MODEL,
+      getProviderModelName(),
       focusedDeconstructJsonSchema,
     );
     const elapsedMs = Date.now() - startedAt;

docs/current-handoff.md

@@ -19,7 +19,7 @@ unless new end-to-end user-flow evidence reopens one of those boundaries.
 
 **Immediate next evidence question:**
 
-Can the real browser UI run an entire investigation using OpenAI/Terra for every LLM stage, without any stage silently reverting to the default Ollama/Qwen provider?
+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
@@ -27,6 +27,12 @@ If YES, the next live experiment is one timed/costed OpenAI UI investigation mea
 - token usage where available
 - approximate cost per investigation
 
+## Server-owned UI journey provider experiment
+
+- Server-only `CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER=openai` centrally resolves the existing OpenAI provider and `gpt-5.6-terra`; without it, normal production resolution remains Ollama/Qwen. An OpenAI key alone does not switch providers.
+- Browser request contracts and client state remain unchanged. Deterministic coverage includes initial start, normal update, episode reconsideration, focused deconstruction, overview synthesis, and Current Understanding synthesis.
+- Zero live calls occurred. Next boundary: one real Playwright-driven Terra investigation measuring user-visible latency, actual LLM-call sequence, and OpenAI usage/cost.
+
 ## Repository checkpoint
 
 - **Branch:** `feature/initial-decomposition-v0.61`

lib/analysis.js

@@ -4,7 +4,7 @@
  */
 
 import { getConfig } from "../lib/config.js";
-import { getProvider } from "../lib/llm/provider.js";
+import { getProvider, getProviderModelName } from "../lib/llm/provider.js";
 import {
   buildPrompt,
   PROMPT_VERSIONS,
@@ -52,7 +52,6 @@ export async function analyseScenario(scenario, opts = {}) {
     return buildErrorResponse("Invalid server configuration", startTime, "500");
   }
 
-  const { OLLAMA_BASE_URL: _ignored, OLLAMA_MODEL } = configResult.config;
   const promptVersion = opts.promptVersion || DEFAULT_PROMPT_VERSION;
 
   // ── Build prompt (experiment seam via env var bridge) ──
@@ -73,7 +72,7 @@ export async function analyseScenario(scenario, opts = {}) {
 
   // ── Call provider ──────────────────────────────────
   const provider = opts.reconstructionProvider ?? getProvider();
-  const reconstructionModelName = opts.reconstructionModelName ?? OLLAMA_MODEL;
+  const reconstructionModelName = opts.reconstructionModelName ?? getProviderModelName();
   let rawResponse;
   let providerApiPath;
   let providerExecution;

lib/config.js

@@ -5,7 +5,29 @@ const envSchema = z.object({
   OLLAMA_MODEL: z.string().min(1),
 });
 
+const openAIExperimentEnvSchema = z.object({
+  OPENAI_API_KEY: z.string().min(1),
+});
+
+export const OPENAI_UI_JOURNEY_EXPERIMENT_PROVIDER = "openai";
+export const OPENAI_TERRA_MODEL = "gpt-5.6-terra";
+
+export function isOpenAIUiJourneyExperiment() {
+  return process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER === OPENAI_UI_JOURNEY_EXPERIMENT_PROVIDER;
+}
+
 export function getConfig() {
+  if (isOpenAIUiJourneyExperiment()) {
+    const parsed = openAIExperimentEnvSchema.safeParse({
+      OPENAI_API_KEY: process.env.OPENAI_API_KEY,
+    });
+    if (!parsed.success) return { ok: false, error: parsed.error.flatten().fieldErrors };
+    return {
+      ok: true,
+      config: { provider: OPENAI_UI_JOURNEY_EXPERIMENT_PROVIDER, modelName: OPENAI_TERRA_MODEL },
+    };
+  }
+
   const parsed = envSchema.safeParse({
     OLLAMA_BASE_URL: process.env.OLLAMA_BASE_URL,
     OLLAMA_MODEL: process.env.OLLAMA_MODEL,
@@ -15,7 +37,7 @@ export function getConfig() {
     return { ok: false, error: parsed.error.flatten().fieldErrors };
   }
 
-  return { ok: true, config: parsed.data };
+  return { ok: true, config: { ...parsed.data, provider: "ollama", modelName: parsed.data.OLLAMA_MODEL } };
 }
 
 export function assertConfig() {

lib/graph/orchestrator.js

@@ -5,7 +5,7 @@
 
 import { analyseScenario } from "../analysis.js";
 import { assertConfig } from "../config.js";
-import { getProvider } from "../llm/provider.js";
+import { getProvider, getProviderModelName } from "@/lib/llm/provider.js";
 import {
   makeGraph,
   startCaseRequestSchema,
@@ -666,8 +666,8 @@ async function updateCaseWithDependencies(body, dependencies = {}) {
   const startedAt = Date.now();
 
   try {
-    const config = dependencies.config ?? assertConfig();
-    modelName = config.OLLAMA_MODEL;
+    if (!dependencies.config) assertConfig();
+    modelName = dependencies.modelName ?? dependencies.config?.modelName ?? dependencies.config?.OLLAMA_MODEL ?? getProviderModelName();
 
     const prompt = buildPrompt({
       situationGraph,
@@ -1185,7 +1185,7 @@ export async function reconsiderCompletedEpisode(epiParams, deps = {}) {
   try {
     // Preserve original priority (deps.modelName > deps.config.OLLAMA_MODEL > getModelName) with assertConfig fallback only when no deps provide a model
     let resolvedConfig = undefined;
-    if (deps.modelName == null && deps.config?.OLLAMA_MODEL == null && deps.config !== null) {
+      if (deps.modelName == null && deps.config?.OLLAMA_MODEL == null && deps.config?.modelName == null && deps.config !== null) {
       const hasOtherDeps = Object.keys(deps).some((k) => k !== "config" && k !== "modelName");
       if (hasOtherDeps) {
         resolvedConfig = undefined; // don't call assertConfig when deps is non-empty with other keys
@@ -1196,8 +1196,9 @@ export async function reconsiderCompletedEpisode(epiParams, deps = {}) {
     const config = deps.config ?? resolvedConfig;
     modelName =
       deps.modelName ??
-      (config != null ? config.OLLAMA_MODEL : undefined) ??
+        (config != null ? (config.modelName ?? config.OLLAMA_MODEL) : undefined) ??
       getModelName?.() ??
+        getProviderModelName() ??
       null;
 
     const promptBuilder = buildEpisodePrompt ?? buildEpisodeAwareGraphPrompt;

lib/llm/provider.js

@@ -1,5 +1,6 @@
 import { z } from "zod";
 import { reconstructionV2Schema } from "../reconstruction/schema.js";
+import { isOpenAIUiJourneyExperiment, OPENAI_TERRA_MODEL } from "../config.js";
 
 /**
  * Provider abstraction — the app calls getProvider() which returns an object
@@ -9,9 +10,15 @@ import { reconstructionV2Schema } from "../reconstruction/schema.js";
  */
 
 export function getProvider() {
+  if (isOpenAIUiJourneyExperiment()) return createOpenAIReconstructionProvider();
   return new OllamaLlmProvider();
 }
 
+/** Server-owned model resolution for the configured application provider. */
+export function getProviderModelName() {
+  return isOpenAIUiJourneyExperiment() ? OPENAI_TERRA_MODEL : process.env.OLLAMA_MODEL ?? null;
+}
+
 /**
  * Experiment-only construction seam. Production provider selection remains Ollama.
  * @param {{ apiKey?: string, fetchImpl?: typeof fetch }} [options]

tests/app/api/cases-overview-route.test.js

@@ -0,0 +1,29 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const mockSynthesize = vi.fn();
+
+vi.mock("@/lib/graph/investigation-overview-synthesis.js", () => ({
+  synthesizeInvestigationOverview: (...args) => mockSynthesize(...args),
+}));
+
+vi.mock("@/lib/llm/provider.js", () => ({
+  getProvider: () => ({ generateReconstruction() {} }),
+  getProviderModelName: () => "gpt-5.6-terra",
+}));
+
+describe("POST /api/cases/overview provider routing", () => {
+  beforeEach(() => mockSynthesize.mockClear());
+
+  it("passes the central provider and model resolution to overview synthesis", async () => {
+    mockSynthesize.mockResolvedValue({ understanding: "Understanding", plausibleInterpretations: "None" });
+    const { POST } = await import("@/app/api/cases/overview/route.js");
+    const response = await POST(new Request("http://localhost/api/cases/overview", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ situationGraph: { nodes: [], edges: [] }, findings: [], plausibleInterpretations: [] }),
+    }));
+
+    expect(response.status).toBe(200);
+    expect(mockSynthesize.mock.calls[0][1]).toMatchObject({ modelName: "gpt-5.6-terra" });
+  });
+});

tests/app/api/cases-start-route.test.js

@@ -39,6 +39,8 @@ describe("app/api/cases/start route", () => {
     await POST(request);
 
     expect(mockStartCase).toHaveBeenCalledWith({ scenario: "Scenario text" });
+    expect(mockStartCase.mock.calls[0][0]).not.toHaveProperty("provider");
+    expect(mockStartCase.mock.calls[0][0]).not.toHaveProperty("modelName");
   });
 
   it("returns 200 on success", async () => {

tests/app/api/cases-update-route.test.js

@@ -72,6 +72,8 @@ describe("app/api/cases/update route", () => {
     );
 
     expect(mockUpdateCase).toHaveBeenCalledWith(body, { applyProposal: true });
+    expect(mockUpdateCase.mock.calls[0][0]).not.toHaveProperty("provider");
+    expect(mockUpdateCase.mock.calls[0][0]).not.toHaveProperty("modelName");
   });
 
   it("invalid JSON returns 400", async () => {

tests/app/api/current-understanding-synthesis-route.test.js

@@ -10,6 +10,7 @@ vi.mock("@/lib/graph/current-understanding-synthesis.js", () => ({
 
 vi.mock("@/lib/llm/provider.js", () => ({
   getProvider: () => ({}),
+  getProviderModelName: () => "gpt-5.6-terra",
 }));
 
 // ── Helpers ─────────────────────────────────────────────────
@@ -45,6 +46,7 @@ describe("POST /api/cases/synthesis — valid request", () => {
     expect(data.success).toBe(true);
     expect(data.currentUnderstanding).toBe("Synthesized result");
     expect(mockSynthesize).toHaveBeenCalledTimes(1);
+    expect(mockSynthesize.mock.calls[0][1]).toMatchObject({ modelName: "gpt-5.6-terra" });
   });
 
   it("returns narrative result on success", async () => {

tests/focused-deconstruct-boundary.test.js

@@ -51,6 +51,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
 
     vi.doMock("@/lib/llm/provider", () => ({
       getProvider: () => makeMockProvider(inventedModelId),
+      getProviderModelName: () => "configured-model",
     }));
 
     const { POST } = await import("../app/api/focused-investigation/deconstruct/route.js");
@@ -97,6 +98,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
     });
     vi.doMock("@/lib/llm/provider", () => ({
       getProvider: () => ({ generateReconstruction }),
+      getProviderModelName: () => "gpt-5.6-terra",
     }));
     const { POST } = await import("../app/api/focused-investigation/deconstruct/route.js");
 
@@ -116,7 +118,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
     expect(response.status).toBe(200);
     expect(generateReconstruction).toHaveBeenCalledWith(
       expect.any(String),
-      process.env.OLLAMA_MODEL,
+      "gpt-5.6-terra",
       focusedDeconstructJsonSchema,
     );
   });
@@ -149,6 +151,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
           providerExecution: { chatRequestAttempted: true },
         }),
       }),
+      getProviderModelName: () => "configured-model",
     }));
 
     const { POST } = await import("../app/api/focused-investigation/deconstruct/route.js");
@@ -228,6 +231,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
           providerExecution: { chatRequestAttempted: true },
         }),
       }),
+      getProviderModelName: () => "configured-model",
     }));
 
     const { POST } = await import("../app/api/focused-investigation/deconstruct/route.js");
@@ -291,6 +295,7 @@ describe("focused-deconstruct targetNodeId identity boundary", () => {
           providerExecution: { chatRequestAttempted: true, chatRequestSucceeded: true },
         }),
       }),
+      getProviderModelName: () => "configured-model",
     }));
 
     const { POST } = await import("../app/api/focused-investigation/deconstruct/route.js");

tests/graph/episode-reasoning-seam.test.js

@@ -1,5 +1,10 @@
 import { beforeEach, describe, expect, it, vi } from "vitest";
 
+vi.mock("@/lib/llm/provider.js", () => ({
+  getProvider: () => ({ generateReconstruction() {} }),
+  getProviderModelName: () => "gpt-5.6-terra",
+}));
+
 // ── Fixtures ────────────────────────────────────────────────
 
 function makePreparedEpisode(overrides = {}) {
@@ -193,4 +198,22 @@ describe("episode reasoning seam (reconsiderCompletedEpisode)", () => {
     else process.env.OLLAMA_MODEL = prevModel;
   });
 
+  it("uses the central provider model resolution when episode mode supplies no model override", async () => {
+    const provider = {
+      generateReconstruction: vi.fn().mockResolvedValue(makeProposalResponse()),
+    };
+    const { reconsiderCompletedEpisode } = await import("@/lib/graph/orchestrator.js");
+
+    const result = await reconsiderCompletedEpisode(
+      { ...TEST_EPISODE, provider },
+      { buildEpisodePrompt: () => "EPISODE_PROMPT" },
+    );
+
+    expect(result.success).toBe(true);
+    expect(provider.generateReconstruction).toHaveBeenCalledWith(
+      "EPISODE_PROMPT",
+      "gpt-5.6-terra",
+    );
+  });
+
 });

tests/llm/provider.test.js

@@ -4,6 +4,7 @@ import {
   createOpenAIStrictSchema,
   createOpenAIReconstructionProvider,
   getProvider,
+  getProviderModelName,
   normaliseOpenAITransportResponse,
   reconstructionJsonSchema,
 } from "@/lib/llm/provider.js";
@@ -11,6 +12,48 @@ import { reconstructionV2Schema } from "@/lib/reconstruction/schema.js";
 import { z } from "zod";
 
 describe("OllamaLlmProvider chat capability detection", () => {
+  it("keeps Ollama and its configured model when no experiment provider is selected", () => {
+    const previousExperimentProvider = process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER;
+    const previousModel = process.env.OLLAMA_MODEL;
+    const previousOpenAIKey = process.env.OPENAI_API_KEY;
+    delete process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER;
+    process.env.OLLAMA_MODEL = "qwen-default";
+    process.env.OPENAI_API_KEY = "present-but-not-selected";
+
+    try {
+      expect(getProvider().constructor.name).toBe("OllamaLlmProvider");
+      expect(getProviderModelName()).toBe("qwen-default");
+    } finally {
+      if (previousExperimentProvider === undefined) delete process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER;
+      else process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER = previousExperimentProvider;
+      if (previousModel === undefined) delete process.env.OLLAMA_MODEL;
+      else process.env.OLLAMA_MODEL = previousModel;
+      if (previousOpenAIKey === undefined) delete process.env.OPENAI_API_KEY;
+      else process.env.OPENAI_API_KEY = previousOpenAIKey;
+    }
+  });
+
+  it("selects the existing OpenAI provider and Terra only for the explicit experiment configuration", () => {
+    const previousExperimentProvider = process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER;
+    const previousModel = process.env.OLLAMA_MODEL;
+    const previousOpenAIKey = process.env.OPENAI_API_KEY;
+    process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER = "openai";
+    process.env.OPENAI_API_KEY = "test-key";
+    process.env.OLLAMA_MODEL = "qwen-default";
+
+    try {
+      expect(getProvider().constructor.name).toBe("OpenAIReconstructionProvider");
+      expect(getProviderModelName()).toBe("gpt-5.6-terra");
+    } finally {
+      if (previousExperimentProvider === undefined) delete process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER;
+      else process.env.CONFIDENCE_ENGINE_EXPERIMENT_PROVIDER = previousExperimentProvider;
+      if (previousModel === undefined) delete process.env.OLLAMA_MODEL;
+      else process.env.OLLAMA_MODEL = previousModel;
+      if (previousOpenAIKey === undefined) delete process.env.OPENAI_API_KEY;
+      else process.env.OPENAI_API_KEY = previousOpenAIKey;
+    }
+  });
+
   it("uses the configured model for the chat probe and keeps the chat path", async () => {
     const originalBaseUrl = process.env.OLLAMA_BASE_URL;
     const fetchSpy = vi.fn()