## Overview
Second PR in the Pick Record stack. Adds a **Round Robin** selection
strategy alongside Random, so an assignment workflow can distribute
records *evenly* across a candidate pool (e.g. rotate company ownership
across a set of workspace members) rather than just randomly.
**Stacked on #21899** — review/merge that one first. This PR's diff
against `main` includes PR 1's commits until #21899 merges.
## What changed
- Widened the `strategy` enum (`RANDOM` → `RANDOM | ROUND_ROBIN`) in the
shared schema and the server input type.
- Editor now shows a **Strategy** selector (Random / Round robin). The
candidate-pool label changed from "Pick at random from" to the neutral
"Pick from" since random is no longer the only mode.
- Executor implements round robin.
## Design decisions & tradeoffs
1. **State store: Redis `incrBy` (atomic), keyed
`pick-record:round-robin:{workspaceId}:{stepId}`.** Round robin needs a
persistent cursor, and workflow runs are **not** serialized — two runs
can execute the same step concurrently — so the increment must be
atomic. `CacheStorageService.incrBy` (workflow cache namespace) is a
single atomic Redis op, needs no schema change, and is already
injectable. Index = `(cursor - 1) % poolSize`.
**Tradeoff — durability:** a Redis flush/eviction resets the cursor,
which restarts the cycle from an offset. That causes a one-time
*fairness drift*, never a *correctness* bug (no double-assignment, since
each increment is atomic). If strict durability is ever required, the
cursor can move to a Postgres counter table with `INSERT … ON CONFLICT …
DO UPDATE SET cursor = cursor + 1 RETURNING cursor` (atomic + durable) —
deliberately **not** done here to avoid a migration for what is, in
practice, an acceptable reset.
2. **Deterministic pool ordering.** The resolved pool is sorted by `id`
before the cursor is applied, so position→record mapping is stable
run-to-run regardless of fetch order. Without this, round robin wouldn't
reliably cycle.
3. **Cursor key uses `stepId`.** Stable across runs of a published
version. Republishing a version may mint new step ids, which resets the
cursor — acceptable and documented here.
4. **Slot-on-increment.** The cursor increments when the step runs
(reserving a position); if a later step in the run fails, that position
is effectively skipped. Minor, acceptable unfairness — flagged rather
than adding cross-step compensation.
## Testing
Added `pick-record-round-robin-workflow.integration-spec.ts`: builds a
workflow with a 3-record pool and `ROUND_ROBIN`, runs it 4 times
sequentially, and asserts the picks are exactly `[p0, p1, p2, p0]` (full
cycle + wraparound) against the deterministically-ordered pool. Passes
locally alongside PR 1's random test (2 suites / 3 tests). `typecheck` +
`lint:diff-with-main` green for shared/server/front.
## Follow-up
- PR 3: `LOAD_BALANCED` (fewest related records wins).
https://claude.ai/code/session_01MuPWZsqf2bmQSevk6fRbX8
---
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Code](https://claude.ai/code/session_01MuPWZsqf2bmQSevk6fRbX8)_
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Félix Malfait
fa6d1394af
