diff --git a/tests/runner-e2e/harness-env.ts b/tests/runner-e2e/harness-env.ts
index 8a98fe1a73..df7596992e 100644
--- a/tests/runner-e2e/harness-env.ts
+++ b/tests/runner-e2e/harness-env.ts
@@ -87,6 +87,30 @@ export function resolvePaperclipRemoteRunnerBinaryForHarness(
     : undefined;
 }
 
+/**
+ * Keep fixture-only provider switches scoped to the one isolated harness that
+ * needs them. In particular, the pinned legacy OpenCode model is routed by the
+ * paid gateway and may not appear in OpenCode's public model catalog.
+ */
+export function buildRunnerE2EProcessEnvironment(
+  source: NodeJS.ProcessEnv,
+  executions: readonly MatrixExecution[],
+): NodeJS.ProcessEnv {
+  const result = { ...source };
+  delete result.OPENCODE_ALLOW_ALL_MODELS;
+  if (
+    executions.length > 0 &&
+    executions.every(
+      (execution) =>
+        execution.profile.generation === "legacy" &&
+        execution.profile.provider === "opencode",
+    )
+  ) {
+    result.OPENCODE_ALLOW_ALL_MODELS = "true";
+  }
+  return result;
+}
+
 /**
  * Build the environment inherited by the Paperclip server. Paid credentials
  * deliberately stay in the launcher/Playwright process and cross the server
diff --git a/tests/runner-e2e/launch.ts b/tests/runner-e2e/launch.ts
index d0fe4ef3d2..ebe10543ca 100644
--- a/tests/runner-e2e/launch.ts
+++ b/tests/runner-e2e/launch.ts
@@ -22,6 +22,7 @@ import { packageEvidence } from "./evidence.js";
 import { classifyFailure, shouldRetryFailure } from "./failure-classifier.js";
 import { buildRunnerCampaign } from "./history.js";
 import {
+  buildRunnerE2EProcessEnvironment,
   resolvePaperclipRemoteRunnerBinaryForHarness,
   resolvePaperclipRunnerBinaryForHarness,
 } from "./harness-env.js";
@@ -395,7 +396,7 @@ async function runAttempt(input: {
       repositoryRoot,
     );
     const childEnv: NodeJS.ProcessEnv = {
-      ...process.env,
+      ...buildRunnerE2EProcessEnvironment(process.env, executions),
       PATH: providerPath,
       PAPERCLIP_RUNNER_E2E_EXECUTION_IDS: JSON.stringify(
         executions.map((candidate) => candidate.id),
diff --git a/tests/runner-e2e/support.test.ts b/tests/runner-e2e/support.test.ts
index c40b6a605d..c1eb609a11 100644
--- a/tests/runner-e2e/support.test.ts
+++ b/tests/runner-e2e/support.test.ts
@@ -10,11 +10,12 @@ import { classifyFailure, shouldRetryFailure } from "./failure-classifier.js";
 import {
   assertIsolatedServerEnvironment,
   buildPaperclipServerEnvironment,
+  buildRunnerE2EProcessEnvironment,
   resolvePaperclipRemoteRunnerBinaryForHarness,
   resolvePaperclipRunnerBinaryForHarness,
   runnerE2EServerControlPaths,
 } from "./harness-env.js";
-import { runnerExecutionById } from "./catalog.js";
+import { runnerExecutionById, runnerMatrix } from "./catalog.js";
 import { assertEmbeddedDatabaseIsolation } from "./instance-isolation.js";
 import { evaluateMatchers } from "./matchers.js";
 import {
@@ -116,6 +117,41 @@ describe("runner E2E local binary resolution", () => {
   });
 });
 
+describe("runner E2E provider environment", () => {
+  const legacyLocal = runnerExecutionById(
+    "core-compatibility.legacy-opencode.local.message-marker",
+  );
+  const legacyDaytona = runnerExecutionById(
+    "core-compatibility.legacy-opencode.daytona.message-marker",
+  );
+  const nativeOpenCode = runnerExecutionById(
+    "core-compatibility.runner-opencode.local.message-marker",
+  );
+  const breadthOpenCode = runnerMatrix.find(
+    (execution) => execution.suite.id === "openrouter-model-breadth",
+  )!;
+
+  it("allows the pinned model only for isolated legacy OpenCode harnesses", () => {
+    for (const execution of [legacyLocal, legacyDaytona]) {
+      expect(
+        buildRunnerE2EProcessEnvironment(
+          { KEEP_ME: "yes", OPENCODE_ALLOW_ALL_MODELS: "ambient" },
+          [execution],
+        ),
+      ).toEqual({ KEEP_ME: "yes", OPENCODE_ALLOW_ALL_MODELS: "true" });
+    }
+
+    for (const execution of [nativeOpenCode, breadthOpenCode]) {
+      expect(
+        buildRunnerE2EProcessEnvironment(
+          { KEEP_ME: "yes", OPENCODE_ALLOW_ALL_MODELS: "ambient" },
+          [execution],
+        ),
+      ).toEqual({ KEEP_ME: "yes" });
+    }
+  });
+});
+
 describe("runner E2E server port allocation", () => {
   it("rejects direct and derived embedded-Postgres collisions", () => {
     expect(runnerE2EServerPortConflictsWithDatabase(44_329)).toBe(true);