## Why
You could not add a transaction by hand to a bank-connected account.
There was no good reason for it: bank sync **only inserts** rows it has
not seen before (dedup runs on `dedup_fingerprint` /
`external_transaction_id`, both `null` on manual rows) and **never
deletes or updates**, so a hand-entered transaction survives every later
sync untouched.
The one thing that genuinely does not make sense is letting a user set a
**balance** on a connected account, because the next sync overwrites it.
That restriction stays.
## What was actually blocking it
Less than it looked. The HTTP endpoint already allowed it,
`ManualBalanceAdjuster` already skipped connected accounts, and the
transaction dialog already handled them (it forces `updateBalance:
false`). Only two surfaces blocked it:
- **MCP** — `WriteTool::writableAccount()` rejected every connected
account for *all* writes. Split into `accountInSpace()` (no connection
check — used by `create_transaction` / `update_transaction`) and
`balanceWritableAccount()` (still rejects connected — used by
`create_balance`).
- **The account detail page** — hid its "Add transaction" button for
connected accounts, even though the same dialog on the transactions page
already offered them in its account picker.
## Also in here
Two problems the change surfaced, both fixed:
- **`EnableBankingSyncer` linked-account watermark** took the newest
transaction of *any* source. With manual rows now able to land on a
connected account, one dated later than the bank's last posting would
shrink the fetch window and skip the bank history in between —
permanently, since the watermark only moves forward. On the QA data this
would have skipped **36 days**. Now restricted to bank-sourced rows.
- **`calculateHistoricalBalances`** derives history by walking back from
a bank-provided reference balance, summing transactions unfiltered.
Counting a hand-entered row subtracts money the bank never had. Now
walks bank-sourced rows only. (Safe before only because manual rows
could not reach a connected account.)
Plus the honesty/copy work:
- `ManualBalanceAdjuster` returns whether it shifted anything, so
`create` / `update` / `delete_transaction` all report `balance_updated`
instead of silently no-opping and letting the agent claim a balance
moved.
- The **OAuth consent screen** and the AI Connector settings page said
"bank-connected accounts stay read-only". That was a trust statement,
and it is no longer true — both now say bank-*synced transactions*
cannot be edited or deleted and connected balances stay untouched.
- `create_balance`'s description no longer contradicts the server
instructions shipped alongside it.
- The transaction dialog now *explains* why the "Update account balance"
checkbox is absent on a connected account instead of just hiding it (it
defaults to on and is localStorage-persisted, so it used to vanish
mid-form with no reason given).
## What stays blocked
- Balances on connected accounts — MCP `create_balance` rejects them,
the adjuster no-ops, the UI shows the explanation instead of the
checkbox.
- Editing or deleting bank/imported transactions — still gated on
`source === manually_created`, unchanged.
## Testing
- `create_transaction` on a connected account leaves its balances alone;
moving a transaction onto a connected account unwinds only the manual
side it came from.
- A manual row survives a sync and does not block the bank's own rows —
the invariant the whole change rests on, previously untested.
- A manual transaction does not move the linked-account sync window.
- The account page offers "Add transaction" on connected accounts, and
hides it on non-transactional ones.
- Full suite: 2047 passing, phpstan clean.
QA'd in the browser end to end (create from a connected account, edit it
afterwards, contrast with a manual account, switch accounts mid-form)
and over real MCP calls against the running server (`create_transaction`
returned `balance_updated: false` on connected / `true` on manual;
`create_balance` refused the connected account).
## Demo
https://github.com/user-attachments/assets/7a7f1cbb-8f68-402d-ba35-3288dd7ea77f
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