Fix FailureDetails JSON serialization and cut v1.7.2

[andystaples]

Summary

Fixes a bug where history_export fails for any orchestration that completes with an error, and cuts release v1.7.2.

task.FailureDetails was a plain class (not a dataclass), so HistoryEvent.to_dict() (asdict + _to_serializable) left it as a raw object and json.dumps raised:

TypeError: Object of type FailureDetails is not JSON serializable

This broke durabletask.extensions.history_export for four event types that carry failure information:

• ExecutionCompletedEvent
• TaskFailedEvent
• SubOrchestrationInstanceFailedEvent
• EntityOperationFailedEvent

Fix

Converted FailureDetails to a @dataclass(frozen=True). This is a root-cause fix rather than a per-call-site workaround:

• Preserves the exact public API — same positional constructor and read-only message / error_type / stack_trace attributes.
• asdict now recurses into it automatically, so all four events serialize to { "message", "error_type", "stack_trace" }.
• Adds value equality/hashing as a bonus.

FailureDetails was the only non-dataclass, non-primitive nested type in history events; every other nested type (OrchestrationInstance, ParentInstanceInfo, TraceContext) is already a dataclass, so this single change covers the general case.

Release v1.7.2

• Bumped durabletask and durabletask.azuremanaged to 1.7.2 (and updated azuremanaged dependency floors).
• Updated both changelogs.

Tests

• Added test_failure_details_is_json_safe in test_serialization.py.
• Full core suite (733 passed) and history_export suite (78 passed) green; flake8 clean.

[Copilot]

Pull request overview

This pull request fixes a JSON-serialization bug in history export for orchestrations that complete with failure, and prepares the repo for the v1.7.2 release by bumping package versions and updating changelogs.

Changes:

• Converted task.FailureDetails into a frozen dataclass so asdict() recurses correctly and history_export output is JSON-serializable.
• Added a regression test ensuring failure-bearing events serialize to JSON-safe dictionaries and the full exported document can be json.loads-parsed.
• Bumped durabletask and durabletask.azuremanaged to 1.7.2, updated azuremanaged dependency floors, and updated both changelogs.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
durabletask/task.py	Makes FailureDetails a frozen dataclass to ensure nested history event serialization is JSON-safe.
tests/durabletask/extensions/history_export/test_serialization.py	Adds a regression test validating FailureDetails serialization and end-to-end JSON export validity.
pyproject.toml	Bumps core package version to 1.7.2.
durabletask-azuremanaged/pyproject.toml	Bumps azuremanaged version to 1.7.2 and raises dependency minimums to durabletask>=1.7.2.
CHANGELOG.md	Documents the v1.7.2 fix for history export JSON serialization.
durabletask-azuremanaged/CHANGELOG.md	Documents the v1.7.2 dependency update.