VS Code Copilot Chat 0.47.1 cannot open CLI 1.0.46 sessions: missing phemeral on permission.requested events

## Summary

VS Code Copilot Chat extension (0.47.1) fails to open any CLI session that contains `permission.requested` (or `permission.completed`) events written by Copilot CLI 1.0.46. The extension's Zod schema requires those events to have `"ephemeral": true` at the root, but the CLI does not emit that field.

This makes it impossible to attach VS Code to a CLI session that has ever asked for a permission — i.e. virtually any non-trivial session.

## Environment

- Copilot CLI: **1.0.46** (latest per `copilot update`)
- VS Code: **1.119.1**
- Copilot Chat extension: **0.47.1**
- OS: Windows 11

## Repro

1. Start a session in Copilot CLI and let it perform any action that triggers a permission prompt (e.g. edit a file).
2. In VS Code, open the Copilot Chat sidebar and try to open that CLI session.

## Expected

Session opens and shows the conversation history.

## Actual

Extension log shows, repeatedly:

```
[error] [CopilotCLI] Failed to parse session : Error: Failed to read JSONL from
C:\Users\\.copilot\session-state\\events.jsonl:
Error: Invalid event at line N: ephemeral: Invalid literal value, expected true.
Event: {"type":"permission.requested","data":{"requestId":"...","permissio...
```

The session pane stays empty.

## Root cause (schema mismatch)

The CLI writes `permission.requested` events with this top-level shape:

```json
{"type":"permission.requested","data":{...},"id":"...","timestamp":"...","parentId":"..."}
```

No `ephemeral` property is present. The extension's parser rejects them with `ephemeral: Invalid literal value, expected true`, i.e. its schema has something like `ephemeral: z.literal(true)` as a required field on these events.

Same error fires for every `permission.requested` event in the file (16 occurrences in my session).

## Suggested fix

Either:
- **CLI side:** emit `"ephemeral": true` on `permission.requested` / `permission.completed` events, or
- **Extension side:** make `ephemeral` optional (or default to `true`) in the Zod schema for permission events.

Whichever is cheaper — but it's currently a hard incompatibility between the latest CLI release and the latest extension release.

## Workaround

After ending the CLI session, patch `events.jsonl` to inject `"ephemeral":true` into every `permission.*` event. Risky because it may break the CLI's own resume logic, so not great as a real solution.