Ensure environment variables are passed to existing terminals #2
Description
Summary
Environment variables set by the extension should be propagated to already-open terminals, not just newly created ones.
Problem
When the extension sets environment variables (e.g., for hook configuration or plan context), these may only be available in terminals opened after the extension activates. Pre-existing terminals do not receive the updated environment variables, which can lead to inconsistent behavior.
Expected Behavior
- Environment variables should be injected into all open terminal instances, not just new ones
- When env vars change (e.g., plan context updates), existing terminals should reflect the updated values
Acceptance Criteria
- Env vars are propagated to terminals that were open before extension activation
- Env var updates are reflected in existing terminals when values change
- No terminal restart should be required for env vars to take effect