Fix abort-path turn extension data plumbing

[jif-oai]

Why

SessionTaskContext carries the current turn's ExtensionData so task runners and cleanup code can use the same turn-scoped extension store. The normal run path builds that context before spawning the task, but abort handling has to rebuild it later from the saved RunningTask.

Preserving the turn's ExtensionData on RunningTask keeps the abort path aligned with the run path instead of losing the turn-scoped extension state during cancellation cleanup.

What Changed

• Store the turn's ExtensionData on RunningTask and use it when rebuilding SessionTaskContext during task abort handling.
• Update direct test ExtensionData::new(...) call sites to pass the turn id expected by the current constructor.

Testing

• Not run locally after creating the PR branch.

[jif-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

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