estimate_tokens() only counted message.content chars, completely
ignoring message.tool_calls[].input JSON. When sent to the API,
tool_use blocks include full input, so the token tracker massively
undercounted — in one session, 303k chars (101k tokens) of tool
input were invisible, showing 39% usage when actual was >100%.
Compaction never triggered, causing an API 400 error.
Added estimate_message_tokens() that accounts for both content and
tool_call input. Updated add_message_with_tokens(), recalculate_tokens(),
and clear_conversation() to use it.
7 unit tests + 1 integration test reproducing the exact session trace.
88d2b9592b