~18% of billed input tokens went to re-sending bytes the model had already seen; the fix below recovers an estimated $0.0884 of $0.12.
timestamp.jsonl | 1 run | 14 calls | models: claude-sonnet-5

Run demo-timestamp-seed7
  billed tokens    cache read 0 | cache write 0 | uncached input 56,880 | output 993
  billed dollars   $0.12  (cache read $0.00 | cache write $0.00 | uncached input $0.11 | output $0.0099)
  redundant input  ~17.7% of billed input tokens re-sent (approx)
  scenarios
    as-billed        $0.12  ########################
    no-cache         $0.12  ########################
    optimal-cache    $0.12  ########################
    fixed-cache    $0.0353  #######
    note (as-billed): exact: real billed usage priced at published rates (ground truth)
    note (no-cache): counterfactual: every billed input token repriced at the full uncached rate (no cache reads, no write premium)
    note (optimal-cache): simulated (approx): documented cache rules — 300s TTL sliding on read, min-cacheable gate, one breakpoint at end of messages; char-based token split scaled to billed totals
    note (fixed-cache): simulated (approx): optimal-cache rules over the breaker-repaired rendering; billed usage totals reused for the token split
  breakers
    volatile-system | first at call index 1 | recovers ~$0.0884
      fix: move the volatile value (timestamp/UUID/counter) out of the system prompt — inject it in the latest user message instead
      evidence: system chars [355:374] at call 1: '...reen.\nSession: [session 2026-07-26 14:03:00]\n\nRepository layout:\n  ...' -> '..... [truncated, 196 chars total]

approx (~): char-based attribution scaled to billed totals; dollar and token totals come from real billed usage.
Report written to report.html
