v13.8.0

Telemetry: observation volume on per-session rollups

Carries generation-side observation volume and type mix on the observer_turn_rollup event so cache-value KPIs survive the migration off the legacy per-occurrence session_compressed / context_injected streams.

What's new

• observer_turn_rollup now sums observations_created and the obs_type_* family (bugfix / discovery / decision / refactor / other) across every compression turn in a session. Paired with total_cost_usd, this makes cost-per-observation and observation-type-by-model derivable from the rollup alone.
• context_injected_rollup carries total_observations_injected and total_tokens_saved_vs_naive — context-cache value (observations served × cost/obs) is now derivable from the rollup.
• scrub.ts whitelist extended for the new aggregate keys; all values are counts/sums only — never names, prompt text, or raw strings.
• Public telemetry.mdx docs updated to document the new rollup fields.

Merge notes

• Merged latest main (Ponytail audit, v13.7.1), which removed fabrication tracking; the now-stale fabrication_count / fabricated_count references were dropped from code and docs accordingly.

Full changes: #3017