Observability: traces, costs, decisions

Repair lab (Module 14, L14.4): traces, costs and decisions are one run, and the harness checks that they agree. The broken stack exits 1 with 3 disagreements: 0 decision events in a trace of a run that made 4, a ledger of 14 calls against 11 trace tool calls, and decision d-route missing from the decision log. The repaired stack exits 0. The ledger is 11, equal to the 11 trace tool calls, and the decision log has 4 entries. A 3600 second clock skew still agrees when the join key is run id, seq and decision id. A wall-clock join does not. A $47 Tuesday bill against a $3 average is an illustration, not a number this cell computes. Seed 0, no model call.

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