diff --git a/src/model/provider.ts b/src/model/provider.ts
index a40cae7..bbd7e9a 100644
--- a/src/model/provider.ts
+++ b/src/model/provider.ts
@@ -1,6 +1,6 @@
 import { z } from 'zod';
 import { createServer, type AddressInfo } from 'node:net';
-import { mkdirSync, writeFileSync } from 'node:fs';
+import { mkdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
 import { join } from 'node:path';
 import { tmpdir } from 'node:os';
 import { spawn, type ChildProcess } from 'node:child_process';
@@ -34,7 +34,7 @@ export interface Provider {
 export const validateModel = (model: string): void => {
   if (!model.includes('/')) {
     throw new Error(
-      `Invalid model format "${model}". Expected "provider/model" (e.g. github-copilot/claude-sonnet-4.6, anthropic/claude-sonnet-4-6, claude/sonnet).`,
+      `Invalid model format "${model}". Expected "provider/model" (e.g. github-copilot/claude-sonnet-4.6, anthropic/claude-sonnet-4-6, claude/sonnet, codex/gpt-5.5).`,
     );
   }
 
@@ -49,6 +49,7 @@ export const validateModel = (model: string): void => {
 export const createProvider = (model: string): Provider => {
   validateModel(model);
   if (model.startsWith('claude/')) return new ClaudeCliProvider(model);
+  if (model.startsWith('codex/')) return new CodexCliProvider(model);
   if (model.startsWith('anthropic/')) return new AnthropicProvider(model);
   return new OpenCodeProvider(model);
 };
@@ -447,6 +448,117 @@ export class ClaudeCliProvider implements Provider {
   }
 }
 
+export class CodexCliProvider implements Provider {
+  private readonly modelAlias: string;
+  private readonly debug: boolean;
+
+  constructor(model: string = 'codex/gpt-5.5') {
+    const slashIdx = model.indexOf('/');
+    this.modelAlias = slashIdx !== -1 ? model.slice(slashIdx + 1) : model;
+    this.debug = process.env.AICC_DEBUG === 'true';
+  }
+
+  name() {
+    return 'codex-cli';
+  }
+
+  warmup(): void {}
+
+  async close(): Promise<void> {}
+
+  async chat(messages: ChatMessage[], _opts?: { maxTokens?: number; temperature?: number }) {
+    if (process.env.AICC_DEBUG_PROVIDER === 'mock') {
+      return JSON.stringify({
+        commits: [
+          {
+            title: 'chore: mock commit from provider',
+            body: '',
+            score: 80,
+            reasons: ['mock mode'],
+          },
+        ],
+        meta: { splitRecommended: false },
+      });
+    }
+
+    const prompt = messages.map((m) => `${m.role.toUpperCase()}: ${m.content}`).join('\n\n');
+
+    // `codex exec` is an agent whose stdout is a live trace, not a clean result,
+    // so `--output-last-message` writes only the final message to a file and we
+    // read the answer from disk. We deliberately do NOT pass `--output-schema`:
+    // it feeds OpenAI strict structured outputs, which reject our shared schema
+    // (they require additionalProperties:false on every object). Instead we rely
+    // on the system prompt's embedded schema + "Return ONLY the JSON object",
+    // exactly as the `claude` provider does, and let extractJSON parse it.
+    // read-only + ephemeral keep it a pure completion that never writes or persists.
+    const dir = join(tmpdir(), `codex-aicc-${process.pid}`);
+    mkdirSync(dir, { recursive: true });
+    const outPath = join(dir, 'last-message.txt');
+
+    const args = [
+      'exec',
+      '--model',
+      this.modelAlias,
+      '--sandbox',
+      'read-only',
+      '--skip-git-repo-check',
+      '--ephemeral',
+      '--color',
+      'never',
+      '--output-last-message',
+      outPath,
+      '-', // read the prompt from stdin
+    ];
+
+    if (this.debug)
+      pdbg('spawning codex cli', { model: this.modelAlias, promptChars: prompt.length });
+
+    return new Promise<string>((resolve, reject) => {
+      const cleanup = () => {
+        try {
+          rmSync(dir, { recursive: true, force: true });
+        } catch {}
+      };
+
+      const proc = spawn('codex', args);
+
+      proc.stdin?.write(prompt);
+      proc.stdin?.end();
+
+      let stderr = '';
+      // stdout is the agent's live trace — ignored in favour of --output-last-message.
+      proc.stderr?.on('data', (chunk: Buffer) => {
+        stderr += chunk.toString();
+      });
+
+      proc.on('error', (err) => {
+        cleanup();
+        reject(err);
+      });
+      proc.on('exit', (code) => {
+        if (code !== 0) {
+          cleanup();
+          reject(new Error(`codex cli exited with code ${code}: ${stderr}`));
+          return;
+        }
+        try {
+          const result = readFileSync(outPath, 'utf8').trim();
+          if (!result) {
+            reject(new Error(`codex cli produced no final message.\n${stderr}`));
+            return;
+          }
+          if (this.debug) pdbg('codex cli response', { resultChars: result.length });
+          resolve(result);
+        } catch (e: any) {
+          reject(new Error(`Failed to read codex cli output: ${e.message}\n${stderr}`));
+        } finally {
+          cleanup();
+        }
+      });
+    });
+  }
+}
+
 export class AnthropicProvider implements Provider {
   private readonly modelID: string;
   private readonly debug: boolean;
diff --git a/src/prompt.ts b/src/prompt.ts
index 31935e4..491fd1a 100644
--- a/src/prompt.ts
+++ b/src/prompt.ts
@@ -19,14 +19,15 @@ const matchesPattern = (filePath: string, pattern: string): boolean => {
 
 const MAX_DIFF_CHARS = 80_000;
 
-const tag = (module: string) =>
-  chalk.dim('[ai-cc]') + chalk.cyan(`[${module}]`);
+const tag = (module: string) => chalk.dim('[ai-cc]') + chalk.cyan(`[${module}]`);
 
 const kv = (k: string, v: unknown) => chalk.dim(k + '=') + chalk.yellow(String(v));
 
 const dbg = (module: string, msg: string, pairs: Record<string, unknown> = {}) => {
   if (process.env.AICC_DEBUG !== 'true') return;
-  const kvStr = Object.entries(pairs).map(([k, v]) => kv(k, v)).join(' ');
+  const kvStr = Object.entries(pairs)
+    .map(([k, v]) => kv(k, v))
+    .join(' ');
   console.error(tag(module), chalk.white(msg), kvStr || '');
 };
 
@@ -180,6 +181,9 @@ export const buildGenerationMessages = (opts: {
   specLines.push(
     'Length Rule: Keep titles concise; prefer 50 or fewer chars; MUST be <=72 including type/scope.',
   );
+  specLines.push(
+    'Body Rules (REQUIRED for non-trivial changes): Populate "body" with 2-5 concise bullet points (each line starting with "- ") explaining WHAT changed and WHY, citing concrete files/functions. Leave "body" empty ONLY for genuinely trivial one-line changes (typo, version bump, pure formatting). Never omit the body for feat, fix, refactor, or multi-file changes, regardless of the repo\'s prevailing title-only style.',
+  );
   specLines.push(
     'Emoji Rule: ' +
       (config.style === 'gitmoji' || config.style === 'gitmoji-pure'
@@ -217,7 +221,11 @@ export const buildGenerationMessages = (opts: {
     },
   ];
 
-  dbg('prompt', 'messages built', { systemChars: messages[0].content.length, userChars: messages[1].content.length, totalChars: messages[0].content.length + messages[1].content.length });
+  dbg('prompt', 'messages built', {
+    systemChars: messages[0].content.length,
+    userChars: messages[1].content.length,
+    totalChars: messages[0].content.length + messages[1].content.length,
+  });
 
   return messages;
 };
diff --git a/test/model.test.ts b/test/model.test.ts
index 4f31b4b..5d13601 100644
--- a/test/model.test.ts
+++ b/test/model.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { extractJSON } from '../src/model/provider.js';
+import { createProvider, CodexCliProvider, extractJSON } from '../src/model/provider.js';
 
 describe('extractJSON', () => {
   it('parses valid JSON', () => {
@@ -18,4 +18,28 @@ Trailing text`;
     const raw = `{ "commits": [ { "title": 5 } ] }`;
     expect(() => extractJSON(raw)).toThrow();
   });
-});
\ No newline at end of file
+});
+
+describe('createProvider', () => {
+  it('routes codex/ models to the Codex CLI provider', () => {
+    const provider = createProvider('codex/gpt-5.5');
+    expect(provider).toBeInstanceOf(CodexCliProvider);
+    expect(provider.name()).toBe('codex-cli');
+  });
+});
+
+describe('CodexCliProvider', () => {
+  it('returns a parseable commit plan in mock mode without spawning codex', async () => {
+    const previous = process.env.AICC_DEBUG_PROVIDER;
+    process.env.AICC_DEBUG_PROVIDER = 'mock';
+    try {
+      const raw = await new CodexCliProvider('codex/gpt-5.5').chat([
+        { role: 'user', content: 'diff' },
+      ]);
+      const plan = extractJSON(raw);
+      expect(plan.commits.length).toBeGreaterThan(0);
+    } finally {
+      process.env.AICC_DEBUG_PROVIDER = previous;
+    }
+  });
+});
diff --git a/test/prompt.test.ts b/test/prompt.test.ts
index 937548e..107f7b1 100644
--- a/test/prompt.test.ts
+++ b/test/prompt.test.ts
@@ -42,4 +42,13 @@ describe('prompt generation', () => {
     });
     expect(msgs[0].content).toMatch(/OPTIONAL single leading gitmoji/);
   });
+  it('requires a body for non-trivial changes', () => {
+    const msgs = buildGenerationMessages({
+      files: baseFiles as any,
+      style: style as any,
+      config: cfg('standard'),
+      mode: 'single',
+    });
+    expect(msgs[0].content).toMatch(/Body Rules \(REQUIRED for non-trivial changes\)/);
+  });
 });