update docs for new audit behavior

docs/guides/audit-against-brokerage.md

@@ -186,15 +186,28 @@ Portfolio Audit  (brokerage is source of truth)
 
 `--verbose` prints the full comparison even when everything reconciles.
 
-### Why "close" counts as a match
+### Discrepancies, and which ones are muted
 
 - **Cash matches to the penny.** It's an exact figure on both sides, so
   any gap is real (e.g. money-market dividend accrual between updates)
-  and worth surfacing.
-- **Securities get ~$1 of slack.** A sub-cent NAV-rounding difference on
-  a six-figure fund position can exceed a dollar without being
-  actionable, so small *value* deltas are tolerated -- but *share-count*
-  mismatches never are.
+  and is surfaced as a warning.
+- **Securities get ~$1 of slack** for sub-cent NAV rounding on large
+  positions. Beyond that, a value delta is a **warning by default** --
+  your records should reconcile to the dollar.
+- **Two cases are muted instead** -- still shown (and still in the
+  totals), just greyed out as "expected, you probably don't care." Muting
+  never hides a discrepancy:
+  - **CDs.** zfin carries a CD at face value while the broker marks it to
+    the secondary market. That gap is muted up to a band computed from
+    the CD's own `rate` and time to maturity (capped at one year's
+    coupon); anything larger still warns. We can't reproduce the broker's
+    exact mark without a live yield, so we bound it instead.
+  - **Options.** zfin tracks options at cost while the broker marks to
+    market, and that gap is unbounded without a live quote. So an account
+    holding open options mutes its account-level value delta -- drill into
+    the per-position export (`--schwab` / `--fidelity`) to check share
+    counts, which are never muted.
+- **Share-count mismatches are never muted.**
 
 ### Institutional share classes
 
@@ -215,7 +228,7 @@ treatment to track drift. See
   CSVs.
 - Matching is only as good as the `institution::` / `account_number::`
   entries you keep in `accounts.srf`.
-- Options and cash are reconciled separately from share counts.
+- Options, CDs, and cash are reconciled separately from share counts.
 
 None of this is a reason to skip it -- it's the single best way to keep
 your records honest -- just know it expects some setup and an occasional