A tool/MCP call could render 2+ times in the timeline (issue #521). The
tool is invoked once — this is a display artifact. The segment de-dup in
MessageBubble keyed on `toolName::toolArgs`, which fails two ways:
- The same logical call rendered on both the live SSE stream and the
reloaded/persisted path can carry differing toolArgs strings
(whitespace / key-order from re-serialization), so the two are NOT
de-duplicated and both survive → the reported duplicate.
- Genuine repeated calls of the same tool with identical args (e.g. shell
/ python retries) share the key and get wrongly collapsed to one.
Prefer the LLM-provided toolCallId (carried end-to-end on both live and
persisted segments, stable across serialization) and fall back to
toolName::toolArgs only for legacy segments without an id. This fixes
both the visible duplication and the over-collapse.
Adds pure-function tests for the de-dup logic.
