T11: dated rates and staleness become data, ahead of the 2026-08-31 flip

The price sheet had two defects of one shape -- a schema that could not
hold the fact it needed, the same criticism the cost survey levelled at
the State Hub.

  CA-16  time-boxed rates are DATA. Sonnet's intro price lived in a
         `# intro ...` comment and was invisible to the collector that
         reads the file. Now promo_input/promo_output/promo_until,
         applied per response at its own timestamp.
  CA-17  the 90-day staleness rule was prose in MetricsAndScenarios 1a
         that every M-D2-CST verdict silently inherited. Now `recorded`
         + `max_age_days` in the sheet, and a stale sheet ABORTS.

Both are exercised by make cost-test: the promo rate must apply before
2026-08-31 and lapse after, and a 102-day-old sheet must trip.

Applying CA-16 moved AC-1 from $93.32 to $93.15 -- the $0.17 CB-EV-0002
predicted, now collected rather than noted. That is a legitimate
retarget under T07's distinction: the instrument disproved the target,
and its output is in this commit. The number has now been stated five
times ($248.46, $92.21, $92.87, $93.32, $93.15), each correction from a
different mechanism.

Evidence tables regenerated from the tool rather than hand-patched,
per CA-15 -- which is the rule that exists because hand-typed tables
were the only thing the adversarial review found wrong.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

benchmarks/baselines/model-prices.toml

@@ -1,6 +1,15 @@
-# USD per million tokens; source: Anthropic pricing, recorded 2026-07-31
-# Governed by specs/MetricsAndScenarios.md §1a — refresh on price change or
-# after 90 days, or new M-D2-CST 'better' verdicts are invalid.
+# USD per million tokens. Source: Anthropic pricing.
+# Governed by specs/CostAccounting.md §9 — a stale sheet invalidates new
+# M-D2-CST `better` verdicts. Staleness is enforced by `make cost-test`,
+# not by this comment.
+#
+# Dated rates are DATA, not comments. A promotional rate written as a
+# comment is invisible to the collector that reads this file: the sonnet
+# intro price sat in a `#` remark and was silently ignored, costing $0.17
+# on a $93.32 pass and heading for a sign flip on 2026-08-31.
+
+recorded = 2026-07-31
+max_age_days = 90
 
 [claude-fable-5]
 input = 10.00
@@ -11,8 +20,13 @@ input = 5.00
 output = 25.00
 
 [claude-sonnet-5]
-input = 3.00    # intro 2.00 through 2026-08-31
-output = 15.00  # intro 10.00 through 2026-08-31
+input = 3.00
+output = 15.00
+# Promotional rate in force through `until` (inclusive); the collector
+# applies it to any response whose timestamp falls on or before that date.
+promo_input = 2.00
+promo_output = 10.00
+promo_until = 2026-08-31
 
 [claude-haiku-4-5]
 input = 1.00