diff --git a/docs/current-handoff.md b/docs/current-handoff.md
index c9da7ea..367543c 100644
--- a/docs/current-handoff.md
+++ b/docs/current-handoff.md
@@ -122,6 +122,12 @@
 - An experiment-only OpenAI Responses API provider apparatus exists for `gpt-5.6-terra`, using the same current v0.5 prompt and canonical reconstruction schema. Production provider selection remains Ollama/Qwen.
 - No live OpenAI calls have occurred. Next boundary: a bounded live semantic comparison, not production migration.
 
+## Reconstruction provider injection seam
+
+- OpenAI provider apparatus exists at `860ee6f`; the canonical helper was previously blocked because `startCase()` and `analyseScenario()` created providers internally.
+- An optional reconstruction-provider injection seam now carries an experiment provider through the same production analysis path. Production callers still default to configured Ollama/Qwen through `getProvider()`.
+- No live calls occurred. Next boundary: exactly one live OpenAI fixed-scenario run through the canonical helper; this is not a production provider migration.
+
 ## Current product architecture
 
 Three distinct routes, not a single page:
diff --git a/lib/analysis.js b/lib/analysis.js
index f75579f..cb5ae92 100644
--- a/lib/analysis.js
+++ b/lib/analysis.js
@@ -23,6 +23,8 @@ const MAX_SCENARIO_LENGTH = 10000;
  * @param {string} scenario - The scenario text to analyse
  * @param {object} [opts]
  * @param {"v0.1" | "v0.2"} [opts.promptVersion="v0.2"] - Prompt version to use
+ * @param {{ generateReconstruction: Function }} [opts.reconstructionProvider] - Experiment-only reconstruction provider override
+ * @param {string} [opts.reconstructionModelName] - Experiment-only model override for an injected provider
  * @returns {Promise<object>} Analysis result with diagnostics
  */
 export async function analyseScenario(scenario, opts = {}) {
@@ -70,14 +72,15 @@ export async function analyseScenario(scenario, opts = {}) {
   }
 
   // ── Call provider ──────────────────────────────────
-  const provider = getProvider();
+  const provider = opts.reconstructionProvider ?? getProvider();
+  const reconstructionModelName = opts.reconstructionModelName ?? OLLAMA_MODEL;
   let rawResponse;
   let providerApiPath;
   let providerExecution;
   try {
     const providerResult = await provider.generateReconstruction(
       promptObj.prompt,
-      OLLAMA_MODEL,
+      reconstructionModelName,
     );
     if (
       providerResult &&
@@ -122,7 +125,7 @@ export async function analyseScenario(scenario, opts = {}) {
   if (resultV2.valid) {
     return buildSuccessResultV2(
       resultV2.data,
-      OLLAMA_MODEL,
+      reconstructionModelName,
       duration,
       promptVersion,
       compatibility,
@@ -137,7 +140,7 @@ export async function analyseScenario(scenario, opts = {}) {
   if (resultV1.valid) {
     return buildSuccessResultV1(
       resultV1.data,
-      OLLAMA_MODEL,
+      reconstructionModelName,
       duration,
       promptVersion,
       compatibility,
@@ -148,7 +151,7 @@ export async function analyseScenario(scenario, opts = {}) {
   return buildPartialResult(
     rawResponseStr,
     resultV2.error ?? resultV1.error,
-    OLLAMA_MODEL,
+    reconstructionModelName,
     duration,
     promptVersion,
     compatibility,
diff --git a/lib/graph/orchestrator.js b/lib/graph/orchestrator.js
index 966ff47..fcc725b 100644
--- a/lib/graph/orchestrator.js
+++ b/lib/graph/orchestrator.js
@@ -359,7 +359,14 @@ export async function startCase(body, dependencies = {}) {
   }
 
   const { scenario, promptVersion } = parsedRequest.data;
-  const analysis = await analyseScenario(scenario, { promptVersion });
+  const analysisOptions = { promptVersion };
+  if (dependencies.reconstructionProvider) {
+    analysisOptions.reconstructionProvider = dependencies.reconstructionProvider;
+  }
+  if (dependencies.reconstructionModelName) {
+    analysisOptions.reconstructionModelName = dependencies.reconstructionModelName;
+  }
+  const analysis = await analyseScenario(scenario, analysisOptions);
 
   if (!analysis.success) {
     return {
diff --git a/scripts/start-case-experiment-helper.cjs b/scripts/start-case-experiment-helper.cjs
index d543473..b3ce8ab 100755
--- a/scripts/start-case-experiment-helper.cjs
+++ b/scripts/start-case-experiment-helper.cjs
@@ -53,7 +53,7 @@ function readScenarioInput(argv) {
   return { scenario: argv.slice(startIdx).join(" ") };
 }
 
-async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
+async function runStartCaseExperiment(scenarioInput, experimentInstruction, options = {}) {
   // ── Experiment seam bridge: supply instruction to production path ──
   const hadEnvVar = process.env.RECONSTRUCTION_EXPERIMENT_INSTRUCTION != null;
   const previousEnvValue = process.env.RECONSTRUCTION_EXPERIMENT_INSTRUCTION;
@@ -61,10 +61,10 @@ async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
     process.env.RECONSTRUCTION_EXPERIMENT_INSTRUCTION = experimentInstruction;
   }
 
-  let startCase;
+  let startCase = options.startCase;
   const isMock = process.env.START_CASE_EXPERIMENT_HELPER_MOCK === "1";
 
-  if (isMock) {
+  if (!startCase && isMock) {
     // Deterministic mode: skip environment checks and use inline test double.
     startCase = async (body) => {
       // Deterministic inline test double — no live model calls.
@@ -81,7 +81,7 @@ async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
         diagnostics: { validationStatus: "mock", modelName: "inline-test-double", graphReferenceValidation: { valid: true, errors: [] } },
       };
     };
-  } else {
+  } else if (!startCase) {
     const baseUrl = assertRequiredEnv("OLLAMA_BASE_URL");
     const model = assertRequiredEnv("OLLAMA_MODEL");
 
@@ -99,7 +99,10 @@ async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
   let result;
   const endToEndStartedAt = Date.now();
   try {
-    result = await startCase(scenarioInput);
+    result = await startCase(scenarioInput, {
+      reconstructionProvider: options.reconstructionProvider,
+      reconstructionModelName: options.reconstructionModelName,
+    });
   } finally {
     // Clean up experiment env var after execution regardless of outcome
     if (experimentInstruction && !hadEnvVar) {
@@ -132,7 +135,8 @@ async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
   };
 }
 
-(async () => {
+if (require.main === module) {
+  (async () => {
   // Import-only mode: prove real production seam without invoking startCase.
   // Used only for deterministic apparatus verification of the import path.
   if (process.env.START_CASE_EXPERIMENT_HELPER_IMPORT_ONLY === "1") {
@@ -183,4 +187,9 @@ async function runStartCaseExperiment(scenarioInput, experimentInstruction) {
     console.log(JSON.stringify(failure));
     process.exit(1);
   }
-})();
+  })();
+}
+
+module.exports = { runStartCaseExperiment };
+
+module.exports = { runStartCaseExperiment };
diff --git a/tests/graph/orchestrator.test.js b/tests/graph/orchestrator.test.js
index 96b4610..4fe3f4f 100644
--- a/tests/graph/orchestrator.test.js
+++ b/tests/graph/orchestrator.test.js
@@ -356,6 +356,24 @@ describe("lib/graph/orchestrator startCase", () => {
     );
   });
 
+  it("forwards an injected reconstruction provider to analyseScenario", async () => {
+    mockAnalyseScenario.mockResolvedValue(makeAnalysisResult());
+    const reconstructionProvider = { generateReconstruction: vi.fn() };
+    const { startCase } = await import("@/lib/graph/orchestrator.js");
+
+    const result = await startCase(
+      { scenario: "Scenario text" },
+      { reconstructionProvider, reconstructionModelName: "experiment-model" },
+    );
+
+    expect(result.success).toBe(true);
+    expect(mockAnalyseScenario).toHaveBeenCalledWith("Scenario text", {
+      promptVersion: undefined,
+      reconstructionProvider,
+      reconstructionModelName: "experiment-model",
+    });
+  });
+
   it("rejects invalid request input without throwing", async () => {
     const { startCase } = await import("@/lib/graph/orchestrator.js");
 
diff --git a/tests/reconstruction/compatibility.test.js b/tests/reconstruction/compatibility.test.js
index 8ec78c8..eb3354a 100644
--- a/tests/reconstruction/compatibility.test.js
+++ b/tests/reconstruction/compatibility.test.js
@@ -112,6 +112,35 @@ describe("normaliseAnalysisResponse", () => {
 });
 
 describe("analyseScenario compatibility", () => {
+  it("uses an injected reconstruction provider with the production prompt path", async () => {
+    const injectedProvider = {
+      generateReconstruction: vi.fn().mockResolvedValue({
+        inputClassification: { primaryType: "other", classificationReason: "test", confidence: "low" },
+        reconstruction: {
+          summary: "summary", actors: [], systemsOrObjects: [], expectedStates: [], observedStates: [],
+          differences: [], knownTransitions: [], unexplainedTransitions: [], contradictions: [],
+          importantUnknowns: [], plausibleInterpretations: [],
+        },
+        evidence: [],
+        nextQuestion: { id: "q1", question: "What next?", targets: [], reason: "test", expectedInformationValue: "low" },
+      }),
+    };
+    const { analyseScenario } = await import("@/lib/analysis.js");
+
+    const result = await analyseScenario("Scenario text", {
+      promptVersion: "v0.3",
+      reconstructionProvider: injectedProvider,
+      reconstructionModelName: "experiment-model",
+    });
+
+    expect(result.success).toBe(true);
+    expect(injectedProvider.generateReconstruction).toHaveBeenCalledWith(
+      "prompt",
+      "experiment-model",
+    );
+    expect(mockGenerateReconstruction).not.toHaveBeenCalled();
+  });
+
   it("preserves an attempted provider API path on provider failure", async () => {
     const providerError = new Error("Provider failed");
     providerError.providerApiPath = "/api/chat";
diff --git a/tests/scripts/start-case-experiment-helper.test.js b/tests/scripts/start-case-experiment-helper.test.js
index f0796eb..688f4e2 100644
--- a/tests/scripts/start-case-experiment-helper.test.js
+++ b/tests/scripts/start-case-experiment-helper.test.js
@@ -14,10 +14,12 @@ import { execFile } from "child_process";
 import { writeFile, unlink } from "fs/promises";
 import { join, dirname } from "path";
 import { fileURLToPath } from "url";
+import { createRequire } from "module";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const rootDir = join(__dirname, "..", "..");
 const helperPath = join(rootDir, "scripts", "start-case-experiment-helper.cjs");
+const require = createRequire(import.meta.url);
 
 function runHelper(args = [], envOverrides = {}) {
   return new Promise((resolve, reject) => {
@@ -128,6 +130,34 @@ describe("start-case-experiment-helper.cjs apparatus", () => {
   // ── D — Success output ──────────────────────────────────────────
 
   describe("D — success output", () => {
+    it("forwards an explicit reconstruction provider through the startCase path", async () => {
+      const { runStartCaseExperiment } = require(helperPath);
+      const reconstructionProvider = { generateReconstruction() {} };
+      const startCase = async (input, dependencies) => {
+        expect(input).toEqual({ scenario: "Provider seam scenario" });
+        expect(dependencies).toMatchObject({
+          reconstructionProvider,
+          reconstructionModelName: "gpt-5.6-terra",
+        });
+        return {
+          success: true,
+          situationGraph: { nodes: [], edges: [] },
+          assessment: null,
+          selectedQuestion: null,
+          summary: "test",
+        };
+      };
+
+      const result = await runStartCaseExperiment(
+        { scenario: "Provider seam scenario" },
+        null,
+        { reconstructionProvider, reconstructionModelName: "gpt-5.6-terra", startCase },
+      );
+
+      expect(result.success).toBe(true);
+      expect(result.summary).toBe("test");
+    });
+
     it("exit code is 0", async () => {
       const result = await runHelper(["Success test scenario"]);
       expect(result.exitCode).toBe(0);