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>

tools/cb-cost.py

@@ -72,16 +72,53 @@ def components(usage):
     }
 
 
-def price_of(prices, model, toks):
+def rates_at(prices, model, when=None):
+    """Input/output rate in force for `model` at ISO instant `when` (CA-16).
+
+    Promotional rates are data, not comments. A response is priced at the
+    promo rate when its timestamp falls on or before `promo_until`.
+    """
+    pr = prices.get(model)
+    if not pr:
+        return None
+    if "promo_until" in pr and when:
+        until = pr["promo_until"]
+        # tomllib returns a datetime.date for a bare TOML date.
+        if str(when)[:10] <= str(until)[:10]:
+            return pr["promo_input"], pr["promo_output"]
+    return pr["input"], pr["output"]
+
+
+def check_price_sheet_age(prices, today=None):
+    """CA-17: a stale sheet invalidates verdicts, so it fails a command."""
+    import datetime as _dt
+
+    recorded = prices.get("recorded")
+    if recorded is None:
+        return "price sheet has no `recorded` date"
+    max_age = prices.get("max_age_days", 90)
+    today = today or _dt.date.today()
+    if isinstance(recorded, _dt.datetime):
+        recorded = recorded.date()
+    age = (today - recorded).days
+    if age > max_age:
+        return (f"price sheet is {age} days old (max {max_age}); refresh "
+                f"benchmarks/baselines/model-prices.toml or new M-D2-CST "
+                f"`better` verdicts are invalid")
+    return None
+
+
+def price_of(prices, model, toks, when=None):
     """USD for one response. Returns None when the model is unpriced (CA-05)."""
     pr = prices.get(model)
     if not pr:
         return None
+    rin, rout = rates_at(prices, model, when)
     cache = prices["cache"]
-    unit = pr["input"] / 1e6
+    unit = rin / 1e6
     return (
         toks["input"] * unit
-        + toks["output"] * pr["output"] / 1e6
+        + toks["output"] * rout / 1e6
         + toks["cache_read"] * unit * cache["read"]
         + toks["write_5m"] * unit * cache["write_5m"]
         + toks["write_1h"] * unit * cache["write_1h"]
@@ -281,8 +318,12 @@ def collect(slug, pin_ref=None):
         # as though it were an answer.
         raise Abort(f"no responses in {len(paths)} transcript(s) — refusing to report")
 
+    stale = check_price_sheet_age(prices)
+    if stale:
+        raise Abort(stale)
+
     for r in responses:
-        r["cost"] = price_of(prices, r["model"], r["toks"])
+        r["cost"] = price_of(prices, r["model"], r["toks"], r["timestamp"])
 
     attribute(responses, commit_index(pin))
 
@@ -298,11 +339,11 @@ def collect(slug, pin_ref=None):
             continue
         by_task[r["task"]] += r["cost"]
         by_model[r["model"]] += r["cost"]
-        pr = prices[r["model"]]
-        unit = pr["input"] / 1e6
+        rin, rout = rates_at(prices, r["model"], r["timestamp"])
+        unit = rin / 1e6
         rates = {
             "input": unit,
-            "output": pr["output"] / 1e6,
+            "output": rout / 1e6,
             "cache_read": unit * cache["read"],
             "write_5m": unit * cache["write_5m"],
             "write_1h": unit * cache["write_1h"],
@@ -456,6 +497,21 @@ def self_test():
     finally:
         os.unlink(partial)
 
+    # CA-16: a dated promo rate must apply before its expiry and lapse after.
+    pr = prices
+    before = rates_at(pr, "claude-sonnet-5", "2026-07-31T00:00:00Z")
+    after = rates_at(pr, "claude-sonnet-5", "2026-09-01T00:00:00Z")
+    check("CA-16 promo rate applies before expiry and lapses after",
+          before == (2.0, 10.0) and after == (3.0, 15.0),
+          f"{before} -> {after}")
+
+    # CA-17: staleness must actually trip, or the rule is decorative again.
+    import datetime as _dt
+    fresh = check_price_sheet_age(pr, _dt.date(2026, 8, 1))
+    stale = check_price_sheet_age(pr, _dt.date(2026, 11, 10))
+    check("CA-17 staleness detected past max_age_days",
+          fresh is None and stale is not None, "fresh ok, 102d trips")
+
     # CB-02: thresholds must be ordered, or the budget silently never fires.
     ap_defaults = {"soft": 10.00, "hard": 22.00}
     check("CB-02 budget thresholds ordered and positive",