Add account balance anchors

README.md

@@ -144,6 +144,8 @@ Finance Duck verifies the callback state, exchanges the returned code for a `ses
 
 Initial synchronization requests the selected number of **calendar months of booked transactions per account**, defaulting to **12 months**. The bank may provide less history. The choice is saved with the bank connection and reused on reconnection. Automatic synchronization then runs **twice a day**, every **12 hours** after the last successful run, overlapping each account's last successful sync by **14 days**. **Sync now** starts a manual synchronization at any time. Existing accounts keep their successful-sync cursors: changing the history choice or reconnecting does **not** backfill them. Older history can be imported with CSV.
 
+**The start balance is anchored, not guessed.** Open banking shares a date-windowed history, so the sum of the recorded rows alone is not the account's real balance — the money from before the window is missing. After a connected cash account's first successful sync, Finance Duck captures the bank's **booked balance** once, with the day it was true, and stores it on the account (`anchor_balance`, `anchor_date`). **Wealth** then derives the start balance — the anchor less every movement booked through the anchor day — shows it as the first line of the account's flow breakdown, and reports the real balance. Only the booked (CLBD) figure is used, never an available balance that includes pending amounts. The anchor is set once and never moved by a later sync; importing older history corrects the derived start balance by itself, and clearing the anchor in the account's edit form makes the next sync capture a fresh one.
+
 **HTTP 429 is a provider rate limit, not evidence that bank consent has expired.** Bank reads honor `Retry-After` and use bounded exponential retries. A longer or exhausted limit pauses further requests until the reported retry time; failed accounts keep their previous sync cursors and imported data. Session checks use the saved account metadata rather than fetching every account's details again. A failed session is reported once instead of also marking each of its accounts unavailable. After the cooldown, **Sync now** can retry; the warning clears after a successful sync. One-time authorization and code-exchange requests are never automatically replayed.
 
 **A rate-limited sync is a wait, not a fault.** While every failing bank has supplied a retry time, the dashboard reports that synchronization retries by itself after that moment, the account card shows a rate-limit badge instead of a connection error, and the background scheduler sleeps until the deadline rather than retrying hourly into a refusal it already knows about. **Sync now** still tries immediately. Any failure without a supplied deadline keeps the hourly retry, and its cause is named where Finance Duck can determine it locally: an expired consent, an HTTP status, an unreachable provider, or a response it cannot use, such as a booked transaction without a booking date. Provider response text is never displayed.