docs(release-notes): week of 2026-10-19 — correct where code-agent traces appear - #1121

Follow-up to #1119. It corrects the Observability for Code Agents in Simulations bullet in the Week of 2026-10-19 section to match what shipped in v1.53.0:

• Where traces appear. Each call in a run has its own Traces tab, in the call drawer next to Transcript. It lists the traces the agent sent during that call and opens each one in a read-only trace view, and a call with no traces shows "No trace for this call". There is no run-level Traces tab, no 20-per-page list and no "Enable observability" link. A run-level tab was added and then replaced by the per-call tab before the release.
• When the page explains a refusal. The environment page shows why observability is off only when it could not be turned on during the build. Refusals when a run starts are not shown on the page, so "always builds … the page shows why" now reads "still builds without it, and when it could not be turned on during the build, the environment page shows why".
• MCP. get_trace and get_span require the trace or span id. A test_execution_id or call_execution_id is accepted alongside it, but doesn't look a trace up on its own.

Gate clean (leak-scan).

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