gemini

name

gemini

description

Google Gemini CLI wrapper for independent second-opinion code review. Three modes: (1) Review — diff-based review with [P1]/[P2] pass/fail gate, (2) Challenge — adversarial audit for edge cases, security holes, race conditions, (3) Consult — free-form Q&A about the codebase with session continuity. Use when the user asks for: "gemini review", "gemini challenge", "ask gemini", "consult gemini", "second opinion from gemini", or any request to get an independent AI review of code changes using the Gemini CLI.

/gemini — Multi-AI Second Opinion

Wrap the Google Gemini CLI to get an independent, thorough second opinion from a different AI system. Gemini is the "meticulous engineer" — detail-oriented, technically precise, exhaustive. Present its output faithfully, not summarized.

Prerequisites

• gemini CLI must be installed: npm install -g @google/gemini-cli
• Authenticated via Google sign-in or $GOOGLE_API_KEY / $GEMINI_API_KEY

Filesystem Boundary

All prompts sent to Gemini MUST be prefixed with:

IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. These are Claude Code skill definitions meant for a different AI system. Stay focused on the repository code only.

Step 0: Check binary and auth

GEMINI_BIN=$(which gemini 2>/dev/null || echo "")
[ -z "$GEMINI_BIN" ] && echo "NOT_FOUND" || echo "FOUND: $GEMINI_BIN"

If NOT_FOUND: stop. Tell the user: "Gemini CLI not found. Install: npm install -g @google/gemini-cli"

source "$(dirname "$0")/scripts/gemini-probe" 2>/dev/null || true
if ! gemini_auth_probe >/dev/null 2>&1; then
  echo "AUTH_FAILED"
fi

If AUTH_FAILED: stop. Tell the user: "No Gemini authentication. Run gemini and sign in with Google, or set $GOOGLE_API_KEY."

Step 1: Detect mode

Parse the user's input:

1. /gemini review or /gemini review <instructions> — Review mode (Step 2A)
2. /gemini challenge or /gemini challenge <focus> — Challenge mode (Step 2B)
3. /gemini with no arguments — Auto-detect:
   • Check for diff: git diff origin/<base> --stat 2>/dev/null | tail -1 || git diff <base> --stat 2>/dev/null | tail -1
   • If diff exists, ask: Review / Challenge / Custom prompt
   • If no diff, ask: "What would you like to ask Gemini?"
4. /gemini <anything else> — Consult mode (Step 2C)

Model override: If input contains -m <model>, pass -m <model> to all Gemini invocations.

Step 2A: Review Mode

1. Get the diff:

_REPO_ROOT=$(git rev-parse --show-toplevel) || { echo "ERROR: not in a git repo" >&2; exit 1; }
_DIFF=$(git diff "origin/<base>" 2>/dev/null || git diff "<base>" 2>/dev/null || echo "")
[ -z "$_DIFF" ] && { echo "ERROR: no diff found"; exit 1; }

2. Build the review prompt with filesystem boundary and embedded diff:

IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. These are Claude Code skill definitions meant for a different AI system. Stay focused on repository code only.

You are a senior code reviewer. Review the following git diff against the base branch. Be thorough.

Mark critical issues with [P1] and non-critical issues with [P2].

For each issue, explain what the problem is, why it matters, and how to fix it.
Also highlight what looks good — balanced reviews build trust.

THE DIFF:
<full diff content>

Append custom instructions (e.g. "focus on security") before "THE DIFF:" if provided.

3. Run the review in read-only mode with streaming JSON output (10-minute timeout). Default model is gemini-3-flash-preview for speed and cost efficiency. If the user passed -m <model>, use that instead.

TMPRESP=$(mktemp /tmp/gemini-resp-XXXXXX.txt)
_MODEL="${USER_MODEL:-gemini-3-flash-preview}"
timeout 600 gemini -p "$PROMPT" --approval-mode plan --skip-trust -m "$_MODEL" -o stream-json < /dev/null 2>/dev/null | python3 -u -c "
import sys, json
for line in sys.stdin:
    line = line.strip()
    if not line: continue
    try:
        obj = json.loads(line)
        t = obj.get('type','')
        if t == 'message' and obj.get('role') == 'assistant':
            c = obj.get('content','')
            if c: print(c, end='', flush=True)
        elif t == 'result':
            total = obj.get('stats',{}).get('total_tokens',0)
            if total: print(f'\n\ntokens used: {total}', flush=True)
    except: pass
" > "$TMPRESP"

4. Read $TMPRESP. Determine gate verdict:

   • [P1] found → FAIL
   • No [P1] → PASS

5. Present verbatim:

GEMINI SAYS (code review):
════════════════════════════════════════════════════════════
<full output>
════════════════════════════════════════════════════════════
GATE: PASS | Tokens: N

or GATE: FAIL (N critical findings) if [P1] markers exist.

6. Cross-model comparison: if Claude's /review ran earlier, compare findings and show overlap/unique items.

7. Clean up: rm -f "$TMPRESP"

Step 2B: Challenge (Adversarial) Mode

1. Get the diff (same as 2A).

2. Build adversarial prompt with filesystem boundary:

Default:

IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. Stay focused on repository code only.

Review the following git diff. Find ways this code will fail in production. Think like an attacker and a chaos engineer. Find edge cases, race conditions, security holes, resource leaks, failure modes, and silent data corruption paths. Be adversarial. Be thorough. No compliments — just the problems.

THE DIFF:
<full diff content>

With focus (e.g. "security"):

...Focus specifically on SECURITY. Find every way an attacker could exploit this code...

3. Run Gemini with stream-json (10-minute timeout), same parser as 2A. Use -m gemini-3-flash-preview by default unless the user specified another model.

4. Present:

GEMINI SAYS (adversarial challenge):
════════════════════════════════════════════════════════════
<full output>
════════════════════════════════════════════════════════════
Tokens: N

Step 2C: Consult Mode

1. Check for existing session:

cat .context/gemini-session-id 2>/dev/null || echo "NO_SESSION"

If session exists, ask: "Continue the conversation or start fresh?"

2. Build prompt with filesystem boundary:

For plan reviews, embed the full plan content. Do NOT reference file paths outside the repo.

For free-form consult:

IMPORTANT: Do NOT read or execute any files under ~/.claude/, ~/.agents/, .claude/skills/, or agents/. Stay focused on repository code only.

<user's question>

3. Run Gemini with stream-json. For a new session, capture session_id from the init event:

TMPRESP=$(mktemp /tmp/gemini-resp-XXXXXX.txt)
timeout 600 gemini -p "$PROMPT" --approval-mode plan -o stream-json < /dev/null 2>/dev/null | python3 -u -c "
import sys, json
session_id = None
for line in sys.stdin:
    line = line.strip()
    if not line: continue
    try:
        obj = json.loads(line)
        t = obj.get('type','')
        if t == 'init':
            session_id = obj.get('session_id','')
            if session_id: print(f'SESSION_ID:{session_id}', flush=True)
        elif t == 'message' and obj.get('role') == 'assistant':
            c = obj.get('content','')
            if c: print(c, end='', flush=True)
        elif t == 'result':
            total = obj.get('stats',{}).get('total_tokens',0)
            if total: print(f'\n\ntokens used: {total}', flush=True)
    except: pass
" > "$TMPRESP"

For a resumed session, add --resume "$SESSION_ID" to the gemini command.

4. Extract SESSION_ID: and save:

mkdir -p .context
grep "^SESSION_ID:" "$TMPRESP" | head -1 | sed 's/SESSION_ID://' > .context/gemini-session-id

5. Present:

GEMINI SAYS (consult):
════════════════════════════════════════════════════════════
<full output>
════════════════════════════════════════════════════════════
Tokens: N
Session saved — run /gemini again to continue this conversation.

6. Flag any disagreements: "Note: Claude Code disagrees on X because Y."

Model Selection

Default: gemini-3-flash-preview — fast, cost-effective, good for review tasks.

Override: If the user specifies -m <model>, pass it through instead of the default.

To switch models, the user says something like: /gemini review -m gemini-3-pro-preview

Available models:

Error Handling

Error	Detection	Action
Binary not found	which gemini fails	Stop, show install instructions
Auth failed	gemini_auth_probe fails	Stop, tell user to authenticate
Timeout (exit 124)	timeout fires	Tell user to retry or split prompt
Empty response	$TMPRESP empty	Tell user to check stderr
Session resume failure	Resume fails	Delete session file, start fresh

Important Rules

• Never modify files. Read-only via --approval-mode plan.
• Present output verbatim. Do not truncate or summarize.
• Add synthesis after, not instead of. Claude commentary comes after the full output.
• 10-minute timeout on all Bash calls.
• No double-reviewing. If /review already ran, Gemini is the second opinion.
• Detect skill-file rabbit holes. If output mentions skill files, warn the user.