feat(core): add vendor-neutral AGENT=gemini environment variable

[sw-square]

Summary

Add a vendor-neutral AGENT=gemini environment variable to all child processes spawned by Gemini CLI, alongside the existing GEMINI_CLI=1.

This allows downstream tools to detect they are being executed by an AI agent using a single, standardized variable — without needing to check for each agent's tool-specific variable (GEMINI_CLI, CLAUDECODE, CODEX_SANDBOX, CURSOR_AGENT, etc.).

Details

Key Changes

• Adds exported constants AGENT_IDENTIFICATION_ENV_VAR (AGENT) and AGENT_IDENTIFICATION_ENV_VAR_VALUE (gemini) in shellExecutionService.ts
• Sets AGENT=gemini in all three child process spawning paths:
  • child_process.spawn — fallback shell execution
  • PTY spawn — primary interactive shell execution
  • MCP stdio transport — MCP server child processes
• Adds test assertions verifying the new variable in both PTY and child_process paths

Why a standard AGENT variable?

Every AI coding agent currently sets its own env var:

Agent	Variable	Value
Gemini CLI	GEMINI_CLI	1
Claude Code	CLAUDECODE	1
Codex CLI	CODEX_SANDBOX	seatbelt
Cursor	CURSOR_AGENT	1
Goose	GOOSE_TERMINAL	1
Amp	(internal)	-

This forces every downstream tool to maintain a detection matrix. A shared AGENT variable (analogous to CI=true) lets tools write one check:

if [[ -n "${AGENT:-}" ]]; then
  # Adapt behavior for AI agent execution
fi

The value (gemini) identifies which agent is running, enabling agent-specific behavior when needed.

Adoption

Goose (PR #7017) and Amp already ship AGENT=<name>. Consumer-side detection is already happening in Bun and Vercel.

See the standardization discussion at agentsmd/agents.md#136.

Related Issues

Relates to #17079

How to Validate

1. Run Gemini CLI locally: npm start
2. Ask it to execute: echo $AGENT
3. Should output: gemini
4. Run unit tests: npx vitest run packages/core/src/services/shellExecutionService.test.ts

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the Gemini CLI by introducing a standardized, vendor-neutral AGENT environment variable. This variable, set to gemini, allows any child process spawned by the CLI to signal its origin as an AI agent. The primary goal is to simplify detection for downstream tools, enabling them to adapt their behavior based on a single, consistent identifier rather than managing a diverse set of agent-specific environment variables. This promotes greater interoperability and a more unified approach to AI agent identification across different platforms.

Highlights

• Vendor-Neutral Agent Identification: Introduced a new vendor-neutral AGENT=gemini environment variable to all child processes spawned by the Gemini CLI, complementing the existing GEMINI_CLI=1.
• Standardization for Downstream Tools: This change allows downstream tools to detect AI agent execution using a single, standardized variable, eliminating the need to check for multiple agent-specific variables.
• Comprehensive Integration: The AGENT=gemini variable is now set across all three child process spawning paths: child_process.spawn (fallback), PTY spawn (primary interactive shell), and MCP stdio transport (MCP server child processes).
• Test Coverage: Added new test assertions to verify the correct propagation of the AGENT environment variable in both PTY and child_process execution paths.

Changelog

• packages/core/src/services/shellExecutionService.test.ts
  • Added assertions to verify the presence and value of the AGENT environment variable in PTY and child process environments.
• packages/core/src/services/shellExecutionService.ts
  • Defined new constants AGENT_IDENTIFICATION_ENV_VAR and AGENT_IDENTIFICATION_ENV_VAR_VALUE for the AGENT environment variable.
  • Injected the AGENT=gemini environment variable into the environment of child processes spawned via child_process.spawn.
  • Injected the AGENT=gemini environment variable into the environment of child processes spawned via PTY.
• packages/core/src/tools/mcp-client.ts
  • Imported the newly defined AGENT_IDENTIFICATION_ENV_VAR and AGENT_IDENTIFICATION_ENV_VAR_VALUE constants.
  • Injected the AGENT=gemini environment variable into the environment of MCP server child processes.

Activity

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[gemini-code-assist]

Code Review

This pull request introduces a vendor-neutral AGENT=gemini environment variable to child processes, which is a good step towards standardization for AI agent detection. The changes are applied consistently across PTY, child_process, and MCP transports, and the tests are updated accordingly. I've found one minor area for improvement regarding code consistency in shellExecutionService.ts.

[gemini-cli]

Hi there! Thank you for your interest in contributing to Gemini CLI.

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