Add codex github actions

Author: niechen

.github/codex/home/config.toml

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+model = "o3"

.github/codex/labels/codex-attempt.md

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+Attempt to solve the reported issue.
+
+If a code change is required, create a new branch, commit the fix, and open a pull request that resolves the problem.
+
+Here is the original GitHub issue that triggered this run:
+
+### {CODEX_ACTION_ISSUE_TITLE}
+
+{CODEX_ACTION_ISSUE_BODY}

.github/codex/labels/codex-review.md

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+Review this PR and respond with a very concise final message, formatted in Markdown.
+
+There should be a summary of the changes (1-2 sentences) and a few bullet points if necessary.
+
+Then provide the **review** (1-2 sentences plus bullet points, friendly tone).
+
+{CODEX_ACTION_GITHUB_EVENT_PATH} contains the JSON that triggered this GitHub workflow. It contains the `base` and `head` refs that define this PR. Both refs are available locally.

.github/codex/labels/codex-triage.md

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+Troubleshoot whether the reported issue is valid.
+
+Provide a concise and respectful comment summarizing the findings.
+
+### {CODEX_ACTION_ISSUE_TITLE}
+
+{CODEX_ACTION_ISSUE_BODY}

.github/workflows/codex.yml

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+name: Codex
+
+on:
+  issues:
+    types: [opened, labeled]
+  pull_request:
+    branches: [main]
+    types: [labeled]
+
+jobs:
+  codex:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+      issues: write
+      pull-requests: write
+    steps:
+      # By default, Codex runs network disabled using --full-auto, so perform
+      # any setup that requires network (such as installing dependencies)
+      # before openai/codex-action.
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run Codex
+        uses: openai/codex/.github/actions/codex@main
+        with:
+          openai_api_key: ${{ secrets.CODEX_OPENAI_API_KEY }}
+          codex_args: --full-auto
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          codex_home: ./.github/codex/home