Fix truncation state persistence bug

[enyst]

This PR proposes a fix for the controller truncation, and a detailed test on multiple session reloads and truncations.

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(openhands)
This PR fixes a bug with truncation state persistence. The start_id was being incorrectly set to truncation_id after _init_history(), causing session reloading to not work correctly.

Changes:

• Store original_start_id at beginning of _init_history() and restore it at end instead of overwriting with truncation_id
• Add comprehensive test for truncation state persistence

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:099c240-nikolaik   --name openhands-app-099c240   docker.all-hands.dev/all-hands-ai/openhands:099c240