Collaborating with Gemini (Codex)

Use Gemini CLI as a collaborator while keeping Codex as the primary implementer.

Host note: this skill is written for a Codex host. When running in another host (e.g., Claude Code), adapt Codex-specific details such as the command-runner timeout and upload paths.

This skill provides a lightweight bridge script that returns structured JSON and supports multi-turn sessions via SESSION_ID.

Core rules

• Gemini is a collaborator; you own the final result and must verify changes locally.
• Do not invoke gemini directly; always use the bridge script (scripts/gemini_bridge.py) so output/session handling stays consistent.
• Prefer file/line references over pasting snippets. Run the bridge with --cd set to the repo root (it sets the gemini process working directory). Use --cd "." only if your CWD is the repo root.
• For code changes, request Unified Diff Patch ONLY and forbid direct file modification.
• Always capture SESSION_ID and reuse it for follow-ups to keep the collaboration conversation-aware.
• Keep a short Collaboration State Capsule updated while this skill is active.
• Default timeout: when invoking via the Codex command runner, set timeout_ms to 600000 (10 minutes) unless a shorter/longer timeout is explicitly required.
• Optional: pass --sandbox to run Gemini in sandbox mode.

Quick start (shell-safe)

⚠️ If your prompt contains Markdown backticks (` like/this ), do not pass it directly via --PROMPT "..." (your shell may treat backticks as command substitution). Use a heredoc instead; see references/shell-quoting.md`.

PROMPT="$(cat <<'EOF'
Review src/auth.py around login() and propose fixes.
OUTPUT: Unified Diff Patch ONLY.
EOF
)"
python3 .codex/skills/collaborating-with-gemini/scripts/gemini_bridge.py --cd "." --PROMPT "$PROMPT"

Output: JSON with success, SESSIONID, agentmessages, and optional error / all_messages.

Multi-turn sessions

# Start a session
PROMPT="$(cat <<'EOF'
Analyze the bug in foo(). Keep it short.
EOF
)"
python3 .codex/skills/collaborating-with-gemini/scripts/gemini_bridge.py --cd "." --PROMPT "$PROMPT"

# Continue the same session
PROMPT="$(cat <<'EOF'
Now propose a minimal fix as Unified Diff Patch ONLY.
EOF
)"
python3 .codex/skills/collaborating-with-gemini/scripts/gemini_bridge.py --cd "." --SESSION_ID "<SESSION_ID>" --PROMPT "$PROMPT"

Prompting patterns (token efficient)

Use assets/prompt-template.md as a starter when crafting --PROMPT.

1) Ask Gemini to open files itself

Provide:

• Entry file(s) and approximate line numbers
• Objective and constraints
• Output format (diff vs analysis)

Avoid:

• Pasting large code blocks
• Multiple competing objectives in one request

2) Enforce safe output for code changes

Append this to prompts when requesting code:

• OUTPUT: Unified Diff Patch ONLY. Strictly prohibit any actual modifications.

3) Use Gemini for what it’s good at

• Alternative solution paths and edge cases
• UI/UX and readability feedback
• Review of a proposed patch (risk spotting, missing tests)

4) Sharing clipboard screenshots with Gemini

Gemini can only read files inside the workspace root (--cd). Codex saves clipboard PNGs into the OS temp directory (e.g. ${TMPDIR:-/tmp}), which Gemini can’t access, and it may refuse ignored paths (e.g. tmp/). Copy the image into .codexuploads/, then reference that path in your prompt. Delete screenshots when done. Do not add .codexuploads/ to .gitignore: Gemini refuses to read ignored paths.

mkdir -p .codex_uploads && cp "${TMPDIR:-/tmp}"/codex-clipboard-<id>.png .codex_uploads/

Advanced flags

• --sandbox: Run Gemini in sandbox mode.
• --model <name>: Override the default Gemini model.
• --return-all-messages: Include all raw messages (tool calls, traces) in output JSON.

Collaboration State Capsule

Keep this short block updated near the end of your reply while collaborating:

[Gemini Collaboration Capsule]
Goal:
Gemini SESSION_ID:
Files/lines handed off:
Last ask:
Gemini summary:
Next ask:

References

• assets/prompt-template.md (prompt patterns)
• references/shell-quoting.md (shell quoting/backticks)