fix: preserve tool_use blocks during condensation regardless of position

[daniel-lxs]

Summary

Fixes orphaned tool_use blocks error during conversation condensation.

Error: ApiProviderError: messages.50: 'tool_use' ids were found without 'tool_result' blocks immediately after: toolu_011CmkW5Ho9AqFuiC84xuYBb

PostHog issue: https://us.posthog.com/error_tracking/019ba58c-53b6-7592-8988-d7518c59512c

Root Cause

The Anthropic API requires every tool_use block in an assistant message to have a corresponding tool_result block in the immediately following user message. During conversation condensation, the bounded search (only last 3 messages) failed to find tool_use blocks that were further back in history, causing orphaned tool_result blocks.

Solution

Replaced the bounded linear search with a performance-optimized indexed lookup:

1. Collect all tool_use IDs we need to find from kept messages
2. Early exit if no tool_results in kept messages
3. Build index in ONE pass through the condensed region (Map of tool_use ID → message)
4. O(1) lookups instead of repeated O(n) searches

Performance Analysis

Scenario	Before (Bounded)	After (Indexed)
No tool_results in kept messages	O(1)	O(1) early exit
1 tool_result, 500 msgs	O(3)	O(n) one pass + O(1) lookup
5 tool_results, 500 msgs	O(15)	O(n) one pass + O(5) lookups

Memory footprint is minimal - only stores references to messages we're looking for.

Testing

All 44 condensation tests pass.

Fixes ROO-516

---

Important

Replaces linear search with indexed lookup in getKeepMessagesWithToolBlocks() to preserve tool_use blocks, preventing orphaned tool_result blocks and improving performance.

• Behavior:
  • Replaces bounded linear search with indexed lookup in getKeepMessagesWithToolBlocks() in index.ts to preserve tool_use blocks regardless of position.
  • Ensures tool_use blocks are preserved even if far back in history, preventing orphaned tool_result blocks.
• Performance:
  • Indexed lookup provides O(1) lookups for tool_use blocks, improving from O(n) linear searches.
  • Early exit if no tool_results in kept messages.
• Testing:
  • Updates tests in index.spec.ts to verify preservation of tool_use blocks and reasoning blocks.
  • All 44 condensation tests pass.

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[roomote]

Rooviewer   See task on Roo Cloud

Review complete. The fix correctly addresses the orphaned tool_use blocks error by replacing the bounded search with an indexed lookup that searches the entire condensed region. One minor cleanup item found:

• Remove unused findLast import from src/core/condense/index.ts

_{Mention @roomote in a comment to request specific changes to this pull request or fix all unresolved issues.}

[roomote]

Minor cleanup: The findLast import from ../../shared/array at line 10 is now unused since this refactoring replaced the linear search with a Map-based lookup. Consider removing it.

_{Fix it with Roo Code or mention @roomote and request a fix.}

[daniel-lxs]

Closing this PR. The Anthropic API requires tool_result to immediately follow tool_use, making them always adjacent. The old bounded search (3 messages back from startIndex) already covered startIndex-1 where an adjacent tool_use would be. The extended search only helps if tool_use and tool_result are non-adjacent, which is an invalid conversation state that cannot occur through normal API interactions. The test case is contrived - it places tool_use at ts:1 and tool_result at ts:9 which the API would reject. If this error is occurring in production, the root cause is something creating invalid message ordering, not a condensation search boundary issue.