chore(cost_model): drop stale AI-USAGE label references

pilot/cost_model.py

@@ -180,7 +180,7 @@ DEFAULT_TIERS = [
 # Observed runs — the calibration anchor
 # ---------------------------------------------------------------------------
 
-# Real usage reported by the AI-USAGE label, summed from opencode's step_finish
+# Real usage reported by opencode's step_finish events. Keep this list
 # events. Keep this list append-only: it is the only thing separating this model
 # from a guess, and the first entry corrected the tier assumptions by ~15x.
 OBSERVED_RUNS: list[dict] = [
@@ -366,10 +366,10 @@ def report(tiers: list[Tier], prs_per_month: int, caching: bool, models: list[st
 
 
 def observed_report(models: list[str]) -> str:
-    """Price the runs actually measured through the AI-USAGE label."""
+    """Price the runs actually measured through the opencode usage telemetry."""
     if not OBSERVED_RUNS:
         return "No observed runs recorded yet."
-    lines = ["Observed runs (measured via the AI-USAGE label)"]
+    lines = ["Observed runs (measured via opencode step_finish events)"]
     for run in OBSERVED_RUNS:
         u = observed_usage(run)
         lines.append(