Filter orphan tool calls when rehydrating database conversations

[Anoop-Kadachi]

Fixes #639.

DatabaseConversationStore::getLatestConversationMessages() currently rehydrates every stored tool call on an assistant row, even if that tool call has no matching tool result.

That can happen when a multi-step agent turn hits its maxSteps limit after the model has requested tools, but before those tool calls are executed. The assistant message can then be stored with pending tool_calls and no corresponding tool_results.

On the next prompt, the stored conversation history is replayed with orphan tool-use IDs. Providers such as Anthropic reject that history with:

tool_use ids were found without tool_result blocks immediately after


Changes
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Filters stored assistant tool_calls during database conversation rehydration so only calls with a matching tool_results.id are replayed.
Preserves assistant text content when all stored tool calls are orphaned.
Skips fully empty assistant rows that only contain orphaned tool calls.
Adds regression coverage for mixed matched/orphan calls, orphan calls with assistant content, and orphan calls without content.

Why
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This prevents one interrupted or max-step-limited agent turn from permanently corrupting future conversation replays.

[pushpak1300]

can you fix conflicts ?