Surfaces the conversation history with one specific peer for the
wheel-side chat_history MCP tool. The filter joins
(source_id = $X OR target_id = $X) so both inbound (peer was sender)
and outbound (peer was recipient) turns appear in the same view,
ordered by created_at, and composes with existing type/source/
since_secs/since_id/limit filters.
Validates peer_id as a UUID at the trust boundary so a malformed
caller can't smuggle SQL fragments via the parameter — the args are
bound but the explicit rejection gives the wheel a cleaner 400
signal than an empty list, and defends against any future code path
that might interpolate the value into a URL or another query.
Tests: 3 new branches (positive filter, composition with
type+source, UUID-shape rejection across 5 malformed inputs).
Mutation-verified: reverting activity.go fails all peer_id tests.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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