Copilot App cannot reopen a session after events.jsonl grows beyond 560 MB

### Short summary

A long-running Copilot App session becomes unavailable after its history log grows too large.

### Affected version or release

v1.1.12 on windows

### Installation context

Locally installed GitHub Copilot App. One local repository session was affected.

### What happened?

The session remained visible in the App, but opening/resuming it failed with:

RPC error -32603: Invalid string length

The session metadata and events.jsonl file were otherwise intact. The file size was approximately 561 MB.

### Steps to reproduce

1. Use a long-running session with large tool outputs.
2. Allow events.jsonl to grow to approximately 561 MB.
3. Close the Copilot App.
4. Try to reopen or resume the session.
5. Observe that the session is listed but cannot be opened.

### Expected behavior

The App should reopen large sessions, or provide a recoverable compaction/error flow instead of making the session inaccessible.

### Additional context

Workaround: I stopped the session, backed up events.jsonl, and reduced it from approximately 561 MB to 27.6 MB by removing older history while retaining the initial events and latest compacted history. The session opened successfully after replacing the file.

No other session metadata changes were required.

Reproduziere den Fehler mit einer Sitzung, deren events.jsonl ungefähr 561 MB groß ist, und verfolge dann den Ablauf zum erneuten Öffnen/Fortsetzen, der den RPC-Fehler -32603: Invalid string length zurückgibt. Vergleiche ihn mit der gesicherten 27,6 MB großen Datei und definiere als erledigt, dass große Sitzungen erneut geöffnet werden können oder ein wiederherstellbarer Komprimierungs-/Fehlerablauf ohne manuelle Bearbeitung des Verlaufs bereitgestellt wird.

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