[FEATURE] Environment selection and visibility when starting Claude Code from Slack

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When starting a Claude Code session from Slack, there are two issues:

1. No environment selection: There is no way to choose which cloud environment to use. The session starts in an environment with no user input.
2. No visibility: It's unclear which environment was selected or why. Did Claude pick one automatically based on some heuristic? Is it always the default? This behavior isn't documented.

I have multiple cloud environments configured (e.g., "Default" and "Debugging") with different tools and configurations. My "Debugging" environment has gcloud CLI pre-installed via a setup script, which I need for certain repositories. When I start a session from Slack, I don't know which environment I'll get, and I can't change it.

Proposed Solution

1. Interactive environment picker: After selecting a repository, show an environment picker (similar to the repo picker) allowing the user to choose which environment to use.
2. Clear visibility: Display which environment was selected at the start of the session, e.g., "Starting session in Debugging environment" or "Using default environment (no preference set)".
3. Documentation: Document the current behavior - how does Claude decide which environment to use for Slack sessions? Is it always the account default? Can it be influenced?

Alternative Solutions

• Support #24379 (per-repository default environment) and show which environment was auto-selected
• Add a Slack command like /claude-env Debugging to set environment preference, or support this in .claude/settings.json

Priority

High - Significant impact on productivity

Feature Category

Configuration and settings

Use Case Example

I work on infrastructure tasks that require gcloud CLI access. I have a "Debugging" environment with gcloud pre-configured. When a teammate reports an issue in Slack and I want to investigate using Claude Code, I tag @Claude but have no idea which environment the session will use, and no way to choose. I often discover mid-session that gcloud isn't available.

Additional Context

Related: #24379 (per-repository default environment)

The Slack integration documentation doesn't mention environment selection or how the environment is determined.