feat(codex): start a codex session at a chosen reasoning effort

codexConfig takes a `reasoningEffort`, one of the levels codex accepts,
and the session starts with `--config model_reasoning_effort=<level>`.
The registry declares one literal per level, gated on the enum, because
an argv token cannot splice a value into a literal.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/cli-registry-spawn-golden.test.ts

@@ -24,6 +24,7 @@
 import { describe, it, expect } from 'vitest';
 import { getCli } from '../src/config/cli-registry/registry.js';
 import { buildSpawnCommandFromRegistry, type SpawnBridgeOptions } from '../src/session-cli-registry-bridge.js';
+import { CODEX_REASONING_EFFORTS } from '../src/types/session.js';
 
 /** A fixed session id, so `--session-id` is stable across runs. */
 const SID = '0f9c2b14-1111-2222-3333-444455556666';
@@ -131,6 +132,18 @@ describe('codex', () => {
   it('resumes with a POSITIONAL subcommand, not a flag', () => {
     expect(cx({ model: 'gpt-5', resumeSessionId: 'roll_42' })).toBe('codex --model gpt-5 resume roll_42');
   });
+
+  it('sends reasoning effort as one model_reasoning_effort config value, for every level', () => {
+    for (const level of CODEX_REASONING_EFFORTS) {
+      expect(cx({ reasoningEffort: level })).toBe(`codex --config model_reasoning_effort=${level}`);
+    }
+  });
+
+  it('keeps reasoning effort ahead of the resume subcommand', () => {
+    expect(cx({ model: 'gpt-5', reasoningEffort: 'high', resumeSessionId: 'roll_42' })).toBe(
+      'codex --model gpt-5 --config model_reasoning_effort=high resume roll_42'
+    );
+  });
 });
 
 describe('gemini', () => {

test/codex-reasoning-effort-schema.test.ts

@@ -0,0 +1,38 @@
+/**
+ * @fileoverview `codexConfig.reasoningEffort` on the create routes.
+ *
+ * The level becomes part of a `--config model_reasoning_effort=<level>` launch token, so the
+ * schema admits only the words codex knows; anything else fails the request rather than
+ * reaching the argv.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { CreateSessionSchema, QuickStartSchema } from '../src/web/schemas.js';
+import { CODEX_REASONING_EFFORTS } from '../src/types/session.js';
+
+describe('codexConfig.reasoningEffort', () => {
+  it('accepts every level codex knows on both create routes', () => {
+    for (const level of CODEX_REASONING_EFFORTS) {
+      const created = CreateSessionSchema.parse({
+        workingDir: '/tmp',
+        mode: 'codex',
+        codexConfig: { reasoningEffort: level },
+      });
+      expect(created.codexConfig?.reasoningEffort).toBe(level);
+      const quick = QuickStartSchema.parse({
+        caseName: 'work',
+        mode: 'codex',
+        codexConfig: { reasoningEffort: level },
+      });
+      expect(quick.codexConfig?.reasoningEffort).toBe(level);
+    }
+  });
+
+  it('rejects a level codex does not know, and anything shaped like shell', () => {
+    for (const reasoningEffort of ['bogus', 'HIGH', 'high; rm -rf /', '']) {
+      expect(() =>
+        CreateSessionSchema.parse({ workingDir: '/tmp', mode: 'codex', codexConfig: { reasoningEffort } })
+      ).toThrow();
+    }
+  });
+});