diff --git a/lib/providers/anthropic.mjs b/lib/providers/anthropic.mjs
index d46de06..8ef45a7 100644
--- a/lib/providers/anthropic.mjs
+++ b/lib/providers/anthropic.mjs
@@ -864,9 +864,37 @@ async function* _spawnAndStream(irRequest, authContext, spawnImpl) {
   const bin = resolveClaudeBin();
   const env = buildSpawnEnv();
 
-  // Inject OAuth token so the CLI can authenticate.
-  // We set it explicitly here so the plugin is self-contained.
-  env.CLAUDE_CODE_OAUTH_TOKEN = auth.accessToken;
+  // OAuth credential strategy:
+  //
+  // Previously this plugin set env.CLAUDE_CODE_OAUTH_TOKEN to the accessToken
+  // value read from ~/.claude/.credentials.json (or keychain). That worked at
+  // call time but defeated the CLI's built-in auto-refresh: when env var is
+  // present, claude reads it directly and never touches credentials.json, so
+  // expired access tokens were never swapped using the refreshToken sitting
+  // right there in the file. The result was a hard 401 cascade every few
+  // hours (access token TTL ≈ 8h) requiring manual keychain → PI231 copy.
+  //
+  // 2026-05-28 spike: with credentials.json present and CLAUDE_CODE_OAUTH_TOKEN
+  // unset, the CLI detects expired accessToken, calls the OAuth token endpoint
+  // with refreshToken, persists the new accessToken/expiresAt back to
+  // credentials.json, and proceeds. Tested on PI231 v2.1.104 with simulated
+  // expiry; the file's expiresAt advanced from "1 min ago" to "8 hours from
+  // now" in a single spawn cycle.
+  //
+  // So: DO NOT inject env.CLAUDE_CODE_OAUTH_TOKEN here. buildSpawnEnv already
+  // forwards process.env (minus ANTHROPIC_*), so if the operator explicitly
+  // set CLAUDE_CODE_OAUTH_TOKEN at OLP boot time, it's still honored — that
+  // path is for users who can't rely on file/keychain (e.g. ephemeral CI).
+  //
+  // The readAuthArtifact() call above is now a preflight check only — verify
+  // creds exist before spawn — but the value is NOT forwarded to the CLI.
+  //
+  // Authority:
+  //   - claude CLI v2.1.104 reads ~/.claude/.credentials.json + refreshes via
+  //     refreshToken (empirically verified PI231 2026-05-28; no public doc cite)
+  //   - OCP server.mjs:864-888 was the historical source of the env-injection
+  //     pattern, kept here for OAuth artifact discovery but no longer for env
+  //     forwarding
 
   // ADR 0009 Amendment 1: system prompt extracted from IR messages,
   // prepended with OLP_SYSTEM_PROMPT_WRAPPER, passed via --system-prompt.
diff --git a/test-features.mjs b/test-features.mjs
index d805d2e..a377fe2 100644
--- a/test-features.mjs
+++ b/test-features.mjs
@@ -17703,4 +17703,71 @@ describe('Suite 41 — ADR 0009 Amendment 1: stream-json transport (Phase 6)', (
     // model value must follow immediately after --model
     assert.equal(args[modelIdx + 1], 'claude-opus-4-7', '--model value must follow the flag');
   });
+
+  // ── 41h: OAuth env-injection regression guard (2026-05-28) ───────────
+  // Previously _spawnAndStream injected env.CLAUDE_CODE_OAUTH_TOKEN from
+  // readAuthArtifact() unconditionally. That defeated the CLI's built-in
+  // refresh: with env var present, claude never reads credentials.json,
+  // so expired accessTokens are never swapped via refreshToken. Result:
+  // hard 401 cascade every ~8h requiring manual keychain copy.
+  // Fix: don't inject. Spawned process inherits process.env via
+  // buildSpawnEnv; the CLI handles file + refresh natively.
+
+  it('41h: _spawnAndStream does NOT set env.CLAUDE_CODE_OAUTH_TOKEN when only file/keychain auth available', async () => {
+    // Capture the env passed to spawn
+    let capturedEnv = null;
+    const fakeSpawn = (_bin, _args, opts) => {
+      capturedEnv = opts.env;
+      // Minimal valid NDJSON: result/success → stop
+      return makeMockSpawnNDJSON([], { skipEarlySpawn: false })(_bin, _args, opts);
+    };
+    // Ensure the process.env CLAUDE_CODE_OAUTH_TOKEN is unset for this test
+    const sentinel = process.env.CLAUDE_CODE_OAUTH_TOKEN;
+    delete process.env.CLAUDE_CODE_OAUTH_TOKEN;
+    __setSpawnImpl(fakeSpawn);
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        messages: [{ role: 'user', content: 'hi' }],
+      });
+      // Provide auth context directly so readAuthArtifact path doesn't matter
+      const it = anthropic.spawn(ir, { accessToken: 'sentinel-should-not-leak-to-env' });
+      try { for await (const _ of it) { /* drain */ } } catch { /* ignored */ }
+      assert.ok(capturedEnv, 'spawn must have been called');
+      assert.equal(
+        capturedEnv.CLAUDE_CODE_OAUTH_TOKEN, undefined,
+        'env.CLAUDE_CODE_OAUTH_TOKEN must NOT be injected — CLI reads credentials.json natively and auto-refreshes',
+      );
+    } finally {
+      __resetSpawnImpl();
+      if (sentinel !== undefined) process.env.CLAUDE_CODE_OAUTH_TOKEN = sentinel;
+    }
+  });
+
+  it('41h-2: _spawnAndStream forwards process.env.CLAUDE_CODE_OAUTH_TOKEN when explicitly set at OLP boot', async () => {
+    let capturedEnv = null;
+    const fakeSpawn = (_bin, _args, opts) => {
+      capturedEnv = opts.env;
+      return makeMockSpawnNDJSON([], { skipEarlySpawn: false })(_bin, _args, opts);
+    };
+    const sentinel = process.env.CLAUDE_CODE_OAUTH_TOKEN;
+    process.env.CLAUDE_CODE_OAUTH_TOKEN = 'operator-explicit-token';
+    __setSpawnImpl(fakeSpawn);
+    try {
+      const ir = makeIR({
+        model: 'claude-sonnet-4-6',
+        messages: [{ role: 'user', content: 'hi' }],
+      });
+      const it = anthropic.spawn(ir, { accessToken: 'from-file' });
+      try { for await (const _ of it) { } } catch { }
+      assert.equal(
+        capturedEnv.CLAUDE_CODE_OAUTH_TOKEN, 'operator-explicit-token',
+        'process.env override must propagate through buildSpawnEnv unchanged',
+      );
+    } finally {
+      __resetSpawnImpl();
+      if (sentinel === undefined) delete process.env.CLAUDE_CODE_OAUTH_TOKEN;
+      else process.env.CLAUDE_CODE_OAUTH_TOKEN = sentinel;
+    }
+  });
 });