# Selective Account Run — Design

**Date:** 2026-07-08
**Status:** Approved (pending spec review)

## Problem

When a migration run fails for some accounts (e.g. transient `use of closed
network connection`), the user wants to re-run **only the affected accounts**,
not the whole task.

An earlier idea — per-error "retry" buttons inside the errors modal — was
rejected: on a `closed network connection` the copy aborts the whole folder
(`copy.go`, the `net.ErrClosed` branch), so the undelivered tail of the folder
never appears in the error list. A per-UID retry would replay only the few
visible errors and leave the invisible tail uncopied, creating a false sense of
completion.

The correct primitive is a **re-run of the selected accounts**. Copy is
idempotent — `IsMigrated`/`MarkMigrated` dedup by message key — so a re-run
skips everything already copied and delivers only the missing tail, covering the
network-drop case fully.

## Solution

Add checkboxes to the accounts table. The main "Run migration" button runs the
selected accounts; with no selection it runs all accounts (current behavior,
preserved).

## Backend

### `orchestrator.Run`

Change signature to:

```go
func (o *Orchestrator) Run(ctx context.Context, taskID int64, trigger string, accountIDs []int64) (int64, error)
```

- `accountIDs == nil || len == 0` → all accounts (unchanged behavior).
- Otherwise, filter the `ListAccountsByTask` result down to the requested IDs
  **before** `gateOK`, so only the selected accounts are gate-checked and run.
- IDs not belonging to the task are silently dropped by the filter (defense in
  depth; the handler also validates).
- If the filter yields zero accounts, return `ErrNotTested` (nothing runnable) —
  reuses the existing 409 path; the handler maps empty selection separately (see
  below).

Call sites updated:
- `scheduler.go` → `Run(ctx, id, "scheduled", nil)` (always all accounts).
- `run.go` (`handleRun`) → passes the parsed IDs.

`runAll`, `runAccount`, counters, `FinishRun`, and task-status reconciliation are
unchanged: they already operate over whatever `accs` slice they are handed.

### `handleRun`

- Parse an **optional** JSON body `{"account_ids": [1,2,3]}`. Empty/absent body
  → `nil` → all accounts.
- Validate parsed IDs against the task's accounts; if a non-empty selection
  resolves to zero valid IDs → `400 Bad Request`.
- Existing error mapping preserved: `ErrNotTested` → 409 "accounts must pass
  connection tests first"; `ErrAlreadyRunning` → 409.

## Frontend

### Accounts table (`TaskDetail.tsx`)

- New leading column with a per-row checkbox; a "select all" checkbox in the
  header (selects only selectable rows).
- State: `selected: Set<number>` of account IDs.
- A row checkbox is disabled when the account has not passed **both** tests
  (`test_src_status`/`test_dst_status` !== 'ok') or the task is `running`.
- "select all" reflects indeterminate/checked state over the selectable rows.

### Run button

- With a non-empty selection: label "Run selected (N)"; calls
  `runTask(id, [...selected])`.
- With no selection: label "Run migration"; calls `runTask(id)` (all).
- Enable gate computed over the **effective set** (selected, or all when none
  selected): every account in that set must be tested OK, and the task must not
  be `running`.
- Side benefit: one untested account no longer blocks running the ready ones —
  select only the ready accounts and run them.

### `api.ts`

```ts
export const runTask = (id: number, accountIds?: number[]) =>
  api(`/api/tasks/${id}/run`, accountIds?.length
    ? jsonBody({ account_ids: accountIds })
    : { method: 'POST' })
```

## Out of scope (YAGNI)

- The errors modal (`AccountErrorsModal`) is untouched; no retry buttons there.
- No new "partial" task status. After a partial run the task status reflects the
  last run's outcome over the accounts that ran — same as today.
- No selection persistence across reloads.

## Testing

- **Backend unit:** `orchestrator.Run` with a subset filters correctly; empty
  filter runs all; unknown IDs dropped; empty-after-filter → `ErrNotTested`.
- **Backend handler:** `handleRun` parses body, validates IDs, maps empty
  selection → 400, absent body → all.
- **Frontend:** manual verification in the running app — select a subset, run,
  confirm only those accounts start (WS `account_started` events), and the
  unselected accounts' counters/status are untouched.