fix: filter orphan tool_result blocks after sliding window truncation

[dwebster123]

Summary

Fixes #11029

When sliding window truncation removes assistant messages containing tool_use blocks, user messages with tool_result blocks referencing those removed tool_use_ids were still being sent to the API. Anthropic's API requires every tool_result to have a corresponding tool_use in the immediately preceding assistant message, so these orphaned references cause the request to be rejected with:

LLM request rejected: unexpected tool_use_id in tool_result blocks

Root Cause

The existing orphan tool_result filtering logic in getEffectiveApiHistory() only ran in the summary (condensation) code path. When there was no summary and only sliding window truncation had been applied, orphan tool_result blocks were not filtered out.

Fix

Added the same orphan tool_result filtering to the no-summary code path in getEffectiveApiHistory():

1. After determining which messages are visible (not truncated), collect all valid tool_use IDs from visible assistant messages
2. Filter out any tool_result blocks in visible user messages that reference tool_use_ids not in the visible set
3. Remove user messages that become empty after filtering

This mirrors the existing pattern already used in the condensation code path.

Tests

Added 3 test cases:

• Orphan tool_result filtered when both assistant and user messages are truncated by truncationParent
• Orphan tool_result filtered when user message survives truncation but referenced assistant is truncated
• Mixed user messages retain non-orphan content while orphan tool_result blocks are stripped

All 5161 existing tests continue to pass.

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Important

Adds orphan tool_result filtering to getEffectiveApiHistory() for sliding window truncation in index.ts.

• Behavior:
  • Adds orphan tool_result filtering to the no-summary path in getEffectiveApiHistory() in index.ts.
  • Filters tool_result blocks referencing non-visible tool_use IDs and removes empty user messages.
• Tests:
  • Adds test cases in index.spec.ts for orphan tool_result filtering when assistant messages are truncated, user messages survive truncation, and mixed content in user messages.
  • Confirms all 5161 existing tests pass.

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[roomote]

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Review complete. No issues found.

The implementation correctly adds orphan tool_result filtering to the no-summary code path in getEffectiveApiHistory(), mirroring the existing pattern from the summary code path. The fix addresses the root cause where orphan tool_result blocks were being sent to Anthropic's API after sliding window truncation removed their corresponding tool_use messages.

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