Two fixes:
1. compact.rs: When the compaction boundary falls at the start of a
tool-result turn, the preceding assistant turn with ToolUse would be
removed — leaving an orphaned role:tool message with no preceding
assistant tool_calls. OpenAI-compat backends reject this with 400.
Fix: after computing raw_keep_from, walk the boundary back until the
first preserved message is not a ToolResult (or its preceding assistant
has been included). Regression test added:
compaction_does_not_split_tool_use_tool_result_pair.
Source: gaebal-gajae multi-turn tool-call 400 repro 2026-04-09.
2. /cost resume: add JSON output:
{kind:cost, input_tokens, output_tokens, cache_creation_input_tokens,
cache_read_input_tokens, total_tokens}
159 CLI + 431 runtime tests pass. Fmt clean.
6e301c8bb3