Environment variable injection for child processes

[kobzevvv]

Why: Database clients (PostgreSQL, MySQL, Redis) and cloud SDKs (GCP, AWS) expect credentials as environment variables (DATABASE_URL, GOOGLE_APPLICATION_CREDENTIALS, AWS_SECRET_ACCESS_KEY). Vault currently only handles HTTP-level auth.

Scope:

• New tool: vault_exec — run a command with secrets injected as env vars
• Secrets never appear in the agent's context
• Audit logging for each exec call

Use cases:

• PostgreSQL: vault_exec("psql", { DB_PASSWORD: "mydb" })
• GCP SDK: vault_exec("gcloud", { GOOGLE_APPLICATION_CREDENTIALS: "gcp-sa" })
• Any CLI tool that reads secrets from environment

Priority: High — unlocks databases and cloud SDKs