## Problem
A task's model fields (`modelProvider`/`modelId` and the
planning/validator
equivalents) are snapshotted once at task-creation time from the
workflow's
model-lane default in `workflow_settings`. Nothing re-syncs, flags, or
surfaces drift when that default is later changed.
Concretely: the `builtin:coding` workflow's execution default was
`claude-sonnet-4-6` until it was corrected on 2026-07-05. Every task
created
before that correction stayed permanently, invisibly pinned to the stale
model id — 52 tasks were found silently stuck on it.
## Fix
- `TaskStore.getModelLaneDrift(workflowId, before, after)`
(`packages/core/src/store.ts`):
read-only diff over the three model lanes
(execution/planning/validator).
For any lane whose provider+modelId actually changed, it lists the
non-terminal (`column` not `archived`/`done`, not soft-deleted) tasks on
that workflow still pinned to the old value. Never mutates `tasks`.
- Wired into `PATCH /workflows/:id/setting-values`
(`packages/dashboard/src/routes/register-workflow-routes.ts`): captures
a
`before` snapshot, runs the existing `updateWorkflowSettingValues`
unchanged, then attaches an optional `modelDrift` field to the response
when a lane change orphans existing tasks. Backward compatible — the
field
is only present when non-empty.
- Operators can act on the surfaced drift via the existing
`POST /tasks/batch-update-models` endpoint; this change intentionally
does
not auto-rewrite any task (avoids touching tasks mid-execution).
## Testing
- New tests in `packages/core/src/__tests__/workflow-settings.test.ts`
(`TaskStore.getModelLaneDrift`): verifies a task pinned to a changed
lane's
old value is surfaced, a task already on the new value and a
`done`-column
task are excluded, and an unrelated/unchanged lane produces no drift
entry.
- `packages/core`: `npx vitest run
src/__tests__/workflow-settings.test.ts` — 24/24 pass.
- `npx tsc --noEmit` clean in both `packages/core` and
`packages/dashboard`.
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Workflow setting updates can now return a lane-based model drift
summary (execution, planning, validator) showing task IDs still pinned
to the previous model configuration.
* The PATCH workflow setting response conditionally includes
`modelDrift` when impacted tasks are found.
* **Bug Fixes**
* Drift detection now compares a consistent “before” snapshot with the
updated values to avoid stale pairing.
* “No workflow selection” tasks are handled correctly based on the
default-workflow behavior.
* **Tests**
* Added coverage for lane drift across model changes and null-selection
inclusion rules.
* **Documentation**
* Added a release note entry for the change.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
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