refactor(chat): expose public load_full_session API to replace private method access (#3189)

[mrveiss]

Summary

• Adds SessionMixin.load_full_session(session_id) public method
• Rewrites conversation_export._load_full_session_data() to call the new public API instead of accessing private members (_get_chats_directory, _decrypt_data)
• Removes duplicated file-loading logic from conversation_export.py

Test plan

• pytest autobot-backend/ — no regressions

Closes #3189

🤖 Generated with Claude Code

[mrveiss]

Code Review — PR #3252

Issue: #3189 — conversation_export accesses private ChatHistoryManager methods
Verdict: Approve with minor note

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What the PR does

Adds SessionMixin.load_full_session(session_id) as a thin public wrapper around _load_session_from_file, then rewrites conversation_export._load_full_session_data() to call the new public API instead of directly accessing _get_chats_directory and _decrypt_data.

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Correctness

• The new method correctly calls _sanitize_session_id before delegating to _load_session_from_file, so path-traversal protection is preserved (same guard used by every other public accessor).
• _resolve_session_file_path already logs logger.warning("Chat session %s not found", session_id) before returning None, so the previously explicit warning in conversation_export.py (line logger.warning("Session file not found for %s", session_id)) is now handled by the lower layer — no regression.
• ValueError raised by _sanitize_session_id on bad input propagates up to _load_full_session_data's bare except Exception handler, which logs it at ERROR level. That is the same outcome as before, and acceptable given this is a service-layer boundary.
• The old code had an inline import os and import aiofiles inside the function body (a minor anti-pattern). The new code eliminates them. Good.
• Backward-compat filename fallback (chat_{session_id}.json) is preserved because it lives in _resolve_session_file_path, which _load_session_from_file already calls.

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CLAUDE.md compliance

Check	Result
Branch target (Dev_new_gui)	OK
Commit format <type>(scope): ... (#3189)	OK
No hardcoded values introduced	OK
encoding='utf-8' — no new file I/O in changed code	N/A
No print() / console.* introduced	OK
Function length ≤ 30 lines	OK (new method is 4 lines)
No _v2/_fix suffixes	OK
Reuses existing code, no duplication	OK — removed 21 lines of duplicated file-loading logic
Copyright header — not a new file	N/A

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Minor note (non-blocking)

The PR description's test plan (pytest autobot-backend/ — no regressions) relies entirely on the existing test suite. No new unit tests are added for load_full_session. Given the method is a two-line wrapper delegating to a well-tested private method, this is acceptable. A follow-up test exercising the happy-path and the invalid-session-id path via load_full_session directly would further harden the public API contract, but it is not required to merge.

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No blocking issues. The refactor is clean, correct, and strictly better than the original.