feat: use isolated session folder for npm run dev and tests

[maxtara]

Summary

When developing Cooper with npm run dev, the app uses the default session folder (~/.copilot/session-state), which pollutes the main session state with test data and makes testing harder.

Proposal

Use a separate, isolated session folder during development:

• npm run dev → Use ~/.copilot/session-state-dev (or branch-specific folder)
• Git hooks + test scripts → Clean/refresh session folder before running
• Each branch gets a fresh session state on startup

Benefits

1. Isolates dev sessions — Main session folder stays clean for production use
2. Easier testing — Fresh state on every test run, no stale data from previous tests
3. Prevents data pollution — Large test sessions don't affect performance profiling
4. Branch isolation — Different branches can have separate test environments

Implementation Ideas

Option 1: Static dev folder via environment variable

Set COPILOT_SESSION_HOME when running dev:

bash COPILOT_SESSION_HOME=~/.copilot/session-state-dev npm run dev

Option 2: Branch-specific folder via environment variable (Recommended)

Set COPILOT_SESSION_HOME_SUFFIX to auto-append branch name. Cooper's code reads the env var and sanitizes the branch name for cross-platform compatibility:

json { "scripts": { "dev": "cross-env COPILOT_SESSION_HOME_SUFFIX=auto electron-vite dev" } }

In Cooper's main process:
``typescript
const homePath = app.getPath('home');
let sessionHome = join(homePath, '.copilot', 'session-state');

if (process.env.COPILOT_SESSION_HOME_SUFFIX === 'auto') {
const branch = execSync('git branch --show-current', { encoding: 'utf8' }).trim();
const safeBranch = branch.replace(/[^a-zA-Z0-9-]/g, '-');
sessionHome = join(homePath, '.copilot', session-state-dev-${safeBranch});
}
``

Benefits:

• Works on Windows, macOS, Linux
• Each branch automatically gets isolated folder
• Switch branches → fresh session state
• Sanitizes special characters (feature/auto-models → feature-auto-models)

Option 3: Git branch-aware folder (code-based detection)

Auto-detect current branch in code without env var, use ~/.copilot/session-state-{branch-name}:

bash npm run dev # Uses ~/.copilot/session-state-feature-auto-models

Option 4: Clean on startup

Add flag to dev script to auto-clean session folder:

bash npm run dev -- --clean-sessions

Related

• Helps with manual testing and performance profiling
• Prevents contamination of production session data
• Makes it easier to test instruction discovery, MCP configs, etc. without side effects