diff --git a/apps/agent-worker/src/materialize-env.ts b/apps/agent-worker/src/materialize-env.ts
new file mode 100644
index 0000000..bc2f902
--- /dev/null
+++ b/apps/agent-worker/src/materialize-env.ts
@@ -0,0 +1,35 @@
+import { mkdir, rm, writeFile } from 'node:fs/promises';
+import path from 'node:path';
+
+import { assertContainedRealPath } from './path-containment';
+
+export type MaterializedSecret = { name: string; value: string };
+
+// Format matches the historical `NAME="value"` env-file layout the agent CLIs
+// source; values are JSON-quoted so newlines/quotes survive.
+export const formatMaterializedEnv = (secrets: MaterializedSecret[]) =>
+  `${secrets
+    .map((secret) => `${secret.name}=${JSON.stringify(secret.value)}`)
+    .join('\n')}\n`;
+
+// Resolves the contained env-file path inside the checkout and writes it 0600
+// so plaintext secrets never sit world/group-readable in the persistent home.
+export const writeMaterializedEnv = async (
+  repoDir: string,
+  envFilePath: string,
+  secrets: MaterializedSecret[],
+): Promise<string> => {
+  const envPath = await assertContainedRealPath(repoDir, envFilePath, {
+    forWrite: true,
+  });
+  await mkdir(path.dirname(envPath), { recursive: true });
+  await writeFile(envPath, formatMaterializedEnv(secrets), { mode: 0o600 });
+  return envPath;
+};
+
+// Removes a previously materialized env file; no-ops when the path is unset or
+// already gone so it is safe on every teardown path.
+export const removeMaterializedEnv = async (envPath: string | undefined) => {
+  if (!envPath) return;
+  await rm(envPath, { force: true });
+};
diff --git a/apps/agent-worker/src/worker.ts b/apps/agent-worker/src/worker.ts
index f07e6cf..4cae2e8 100644
--- a/apps/agent-worker/src/worker.ts
+++ b/apps/agent-worker/src/worker.ts
@@ -30,6 +30,7 @@ import {
 } from './git';
 import { getInstallationToken, openDraftPullRequest } from './github';
 import { createHeartbeatController } from './heartbeat-controller';
+import { removeMaterializedEnv, writeMaterializedEnv } from './materialize-env';
 import { assertContainedRealPath } from './path-containment';
 import { createRedactor, truncate } from './redact';
 import {
@@ -50,6 +51,8 @@ type ActiveWorkspace = AdapterWorkspace & {
   cancelRequested?: boolean;
   resolveTurn?: () => void;
   lastRecordedDiffSignature?: string;
+  // Absolute path of the last materialized env file so teardown can delete it.
+  materializedEnvPath?: string;
 };
 
 type FileTreeNode = {
@@ -717,16 +720,11 @@ const recordChangedFiles = async (
 const materializeEnvFile = async (workspace: ActiveWorkspace) => {
   const { claim, repoDir } = workspace;
   if (!claim.job.materializeEnvFile || !claim.job.envFilePath) return;
-  const envPath = await assertContainedRealPath(
+  workspace.materializedEnvPath = await writeMaterializedEnv(
     repoDir,
     claim.job.envFilePath,
-    { forWrite: true },
+    claim.secrets,
   );
-  await mkdir(path.dirname(envPath), { recursive: true });
-  const content = `${claim.secrets
-    .map((secret) => `${secret.name}=${JSON.stringify(secret.value)}`)
-    .join('\n')}\n`;
-  await writeFile(envPath, content);
   await appendEvent(
     claim.job._id,
     'info',
@@ -1194,6 +1192,9 @@ export const sendWorkspaceMessage = async (
   if (workspace.agentTurnActive) {
     throw new Error('Wait for the current agent turn to finish or abort it.');
   }
+  // Re-materialize the env file fresh each turn so it is present for the
+  // adapter and can be removed between turns / on teardown.
+  await materializeEnvFile(workspace);
   if (options.recordUserMessage ?? true) {
     await appendMessage({
       jobId: claim.job._id,
@@ -1376,6 +1377,8 @@ const teardownActiveWorkspace = async (args: {
     abortAgent: args.abortAgent
       ? async () => await abortWorkspaceAgentForWorkspace(workspace)
       : undefined,
+    removeMaterializedEnv: async () =>
+      await removeMaterializedEnv(workspace.materializedEnvPath),
     markStopped: async () =>
       await markWorkspaceStopped(workspace.claim.job._id, args.workspaceStatus),
     release: () => workspace.boxHandle.release(),
diff --git a/apps/agent-worker/src/workspace-teardown.ts b/apps/agent-worker/src/workspace-teardown.ts
index 9fac3ab..72c116d 100644
--- a/apps/agent-worker/src/workspace-teardown.ts
+++ b/apps/agent-worker/src/workspace-teardown.ts
@@ -5,6 +5,7 @@ export const teardownWorkspace = async (steps: {
   removeActive: TeardownStep;
   appendEvent?: TeardownStep;
   abortAgent?: TeardownStep;
+  removeMaterializedEnv?: TeardownStep;
   markStopped?: TeardownStep;
   closeAgent?: TeardownStep;
   stopContainer?: TeardownStep;
@@ -27,6 +28,7 @@ export const teardownWorkspace = async (steps: {
   await Promise.all(immediate);
   await call(steps.appendEvent);
   await call(steps.abortAgent);
+  await call(steps.removeMaterializedEnv);
   await call(steps.markStopped);
   await call(steps.closeAgent);
   await call(steps.stopContainer);
diff --git a/apps/agent-worker/tests/unit/materialize-env.test.ts b/apps/agent-worker/tests/unit/materialize-env.test.ts
new file mode 100644
index 0000000..31ffb8c
--- /dev/null
+++ b/apps/agent-worker/tests/unit/materialize-env.test.ts
@@ -0,0 +1,58 @@
+import { access, mkdtemp, readFile, rm, stat } from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+import { afterEach, describe, expect, test } from 'vitest';
+
+import {
+  removeMaterializedEnv,
+  writeMaterializedEnv,
+} from '../../src/materialize-env';
+
+const tempDirs: string[] = [];
+
+const mode = async (filePath: string) => (await stat(filePath)).mode & 0o777;
+
+const exists = async (filePath: string) =>
+  access(filePath).then(
+    () => true,
+    () => false,
+  );
+
+describe('materialize env', () => {
+  afterEach(async () => {
+    await Promise.all(
+      tempDirs.map((dir) => rm(dir, { force: true, recursive: true })),
+    );
+    tempDirs.length = 0;
+  });
+
+  test('writes the env file 0600 at the returned path with quoted values', async () => {
+    const repoDir = await mkdtemp(path.join(os.tmpdir(), 'spoon-env-'));
+    tempDirs.push(repoDir);
+
+    const envPath = await writeMaterializedEnv(repoDir, '.env.local', [
+      { name: 'A', value: 'x' },
+    ]);
+
+    await expect(exists(envPath)).resolves.toBe(true);
+    await expect(mode(envPath)).resolves.toBe(0o600);
+    await expect(readFile(envPath, 'utf8')).resolves.toBe('A="x"\n');
+  });
+
+  test('removeMaterializedEnv deletes an existing file and no-ops when absent', async () => {
+    const repoDir = await mkdtemp(path.join(os.tmpdir(), 'spoon-env-'));
+    tempDirs.push(repoDir);
+
+    const envPath = await writeMaterializedEnv(repoDir, '.env.local', [
+      { name: 'A', value: 'x' },
+    ]);
+    await expect(exists(envPath)).resolves.toBe(true);
+
+    await removeMaterializedEnv(envPath);
+    await expect(exists(envPath)).resolves.toBe(false);
+
+    // No-ops when the file is already gone or the path is undefined.
+    await expect(removeMaterializedEnv(envPath)).resolves.toBeUndefined();
+    await expect(removeMaterializedEnv(undefined)).resolves.toBeUndefined();
+  });
+});