diff --git a/docs/current-handoff.md b/docs/current-handoff.md
index 2b9b2d7..c9da7ea 100644
--- a/docs/current-handoff.md
+++ b/docs/current-handoff.md
@@ -116,6 +116,12 @@
 - This increment adds only a final semantic-preservation self-check, testing instruction salience rather than missing semantic specification. No live model calls were made.
 - Next boundary: one manual fixed-scenario Postman production run, scoring C first while checking A/B/D1/D2/E and unsupported expansion or causal strengthening for regressions.
 
+## OpenAI reconstruction-provider experiment apparatus
+
+- Structural Ollama/provider issues were previously fixed; current semantic comparison now warrants testing model-compliance variance.
+- 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.
+
 ## Current product architecture
 
 Three distinct routes, not a single page:
diff --git a/lib/llm/provider.js b/lib/llm/provider.js
index 04f3e16..aec4778 100644
--- a/lib/llm/provider.js
+++ b/lib/llm/provider.js
@@ -12,6 +12,14 @@ export function getProvider() {
   return new OllamaLlmProvider();
 }
 
+/**
+ * Experiment-only construction seam. Production provider selection remains Ollama.
+ * @param {{ apiKey?: string, fetchImpl?: typeof fetch }} [options]
+ */
+export function createOpenAIReconstructionProvider(options = {}) {
+  return new OpenAIReconstructionProvider(options);
+}
+
 function recoverJson(raw) {
   if (typeof raw !== "string") return raw;
   const trimmed = raw.trim();
@@ -294,3 +302,56 @@ class OllamaLlmProvider {
     }
   }
 }
+
+class OpenAIReconstructionProvider {
+  constructor({ apiKey = process.env.OPENAI_API_KEY, fetchImpl = fetch } = {}) {
+    this.apiKey = apiKey;
+    this.fetchImpl = fetchImpl;
+  }
+
+  async generateReconstruction(prompt, modelName = "gpt-5.6-terra") {
+    if (!this.apiKey) throw new Error("OPENAI_API_KEY is not set");
+
+    const response = await this.fetchImpl("https://api.openai.com/v1/responses", {
+      method: "POST",
+      headers: {
+        Authorization: `Bearer ${this.apiKey}`,
+        "Content-Type": "application/json",
+      },
+      body: JSON.stringify({
+        model: modelName,
+        input: prompt,
+        text: {
+          format: {
+            type: "json_schema",
+            name: "reconstruction",
+            strict: true,
+            schema: reconstructionJsonSchema,
+          },
+        },
+      }),
+    });
+
+    if (!response.ok) {
+      const body = await response.text();
+      const error = new Error(
+        `OpenAI Responses API returned ${response.status}: ${body}`,
+      );
+      error.providerApiPath = "/v1/responses";
+      throw error;
+    }
+
+    const data = await response.json();
+    const outputText = data.output_text;
+    if (typeof outputText !== "string") {
+      const error = new Error("OpenAI Responses API returned no output_text");
+      error.providerApiPath = "/v1/responses";
+      throw error;
+    }
+
+    return {
+      response: recoverJson(outputText),
+      providerApiPath: "/v1/responses",
+    };
+  }
+}
diff --git a/tests/llm/provider.test.js b/tests/llm/provider.test.js
index a8fe8a1..7a79675 100644
--- a/tests/llm/provider.test.js
+++ b/tests/llm/provider.test.js
@@ -1,5 +1,9 @@
 import { describe, expect, it, vi } from "vitest";
-import { __resetChatSupportForTests, getProvider } from "@/lib/llm/provider.js";
+import {
+  __resetChatSupportForTests,
+  createOpenAIReconstructionProvider,
+  getProvider,
+} from "@/lib/llm/provider.js";
 
 describe("OllamaLlmProvider chat capability detection", () => {
   it("uses the configured model for the chat probe and keeps the chat path", async () => {
@@ -114,4 +118,65 @@ describe("OllamaLlmProvider chat capability detection", () => {
       else process.env.OLLAMA_BASE_URL = originalBaseUrl;
     }
   });
+});
+
+describe("OpenAI reconstruction provider experiment seam", () => {
+  it("uses the Responses API with the canonical strict reconstruction schema", async () => {
+    const fetchSpy = vi.fn().mockResolvedValue({
+      ok: true,
+      json: async () => ({ output_text: '{"reconstruction":"result"}' }),
+    });
+    const provider = createOpenAIReconstructionProvider({
+      apiKey: "test-key",
+      fetchImpl: fetchSpy,
+    });
+
+    const result = await provider.generateReconstruction(
+      "current reconstruction prompt",
+    );
+    const request = JSON.parse(fetchSpy.mock.calls[0][1].body);
+    const schemaText = JSON.stringify(request.text.format.schema);
+
+    expect(fetchSpy).toHaveBeenCalledWith(
+      "https://api.openai.com/v1/responses",
+      expect.objectContaining({ method: "POST" }),
+    );
+    expect(request).toMatchObject({
+      model: "gpt-5.6-terra",
+      input: "current reconstruction prompt",
+      text: {
+        format: {
+          type: "json_schema",
+          name: "reconstruction",
+          strict: true,
+        },
+      },
+    });
+    expect(schemaText).toContain("relationship");
+    expect(schemaText).toContain("evidenceType");
+    expect(schemaText).toContain("primaryType");
+    expect(schemaText).toContain("secondaryTypes");
+    expect(schemaText).toContain("confidence");
+    expect(schemaText).toContain("importance");
+    expect(result).toEqual({
+      response: { reconstruction: "result" },
+      providerApiPath: "/v1/responses",
+    });
+  });
+
+  it("surfaces Responses API failures without inventing reconstruction content", async () => {
+    const provider = createOpenAIReconstructionProvider({
+      apiKey: "test-key",
+      fetchImpl: vi.fn().mockResolvedValue({
+        ok: false,
+        status: 429,
+        text: async () => "rate limited",
+      }),
+    });
+
+    await expect(provider.generateReconstruction("prompt")).rejects.toMatchObject({
+      providerApiPath: "/v1/responses",
+      message: "OpenAI Responses API returned 429: rate limited",
+    });
+  });
 });
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