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fix(display): handle small max_len values in build_tool_preview() - #9477
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When max_len < 4, the truncation logic `preview[:max_len - 3] + '...'` produces a negative slice index, resulting in output that exceeds max_len. For max_len < 4, hard-truncate to max_len without ellipsis since there is no room for even one character plus '...'. Also fixes the existing test assertion that incorrectly allowed len(result) <= 43 instead of <= 40 for max_len=40. Fixes NousResearch#9439
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CI note: The |
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Closing to reduce PR backlog. The fix is still valid — happy to reopen or resubmit if there's interest. Thanks! |
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`build_tool_preview()`'s generic-key fallback and the cute-message helpers still truncated with a bare `text[:max_len - 3] + "..."`; for max_len 1-3 the slice goes negative and returns almost the whole string (27 chars for max_len=1). `_truncate_preview` already had the guard, so the two code paths disagreed. One truncation helper (`_tail_trunc`) with the guard, used everywhere; the head-truncating `_cute_path` gets the same clamp. Salvage of PR #48483 by @HeLLGURD (current-code fix); the earliest reports and patches were #9464 (@LarHope), #9477 (@kagura-agent) and #9497. Co-authored-by: LarHope <12761142+LarHope@users.noreply.github.com> Fixes #9439
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Problem
build_tool_preview()inagent/display.pybreaks itsmax_lencontract whenmax_len < 4. The truncation logic:produces a negative slice index for
max_lenvalues of 1, 2, or 3, resulting in output that exceeds the specifiedmax_len.For example, with
max_len=1andpreview="hello":preview[1-3]→preview[-2]→"lo"+"..."→"lo..."(length 5, violates max_len=1)Fix
When
max_len < 4, hard-truncate tomax_lenwithout ellipsis, since there is no room for even one character plus"...". Formax_len >= 4, the existing ellipsis logic works correctly.Also fixes an incorrect existing test assertion that allowed
len(result) <= 43instead of<= 40formax_len=40.Tests
Added 7 new test cases covering:
max_len=0(unlimited — no truncation)max_len=1, 2, 3(small values — hard truncate, no ellipsis)max_len=4(first value where ellipsis fits)All 31 display tests pass. Full test suite shows no regressions.
Fixes #9439