> **Re-landing the second half of #3031.** That PR merged into #3029's
branch and only its first commit reached `main` — the arity rule
shipped, the interface rule and its finding did not. Verified on `main`:
the gate reports *"7 mirrored function(s)"* with no interface count, and
the dead prop below is still there.
## What
The arity rule covers exported functions. The same files also mirror
**interfaces**, which is the larger surface — six copies of
`PluginDashboardViewContext` alone.
**One direction only.** A mirror may declare *fewer* properties, and all
six do (6, 8, 7, 7, 3, 6 against the real nine) because a plugin mirrors
the fields it uses. Demanding equality would fail every plugin for not
using everything — which is how a check gets ignored and then deleted. A
property the real type **doesn't have** is the drift that matters: a
rename nobody propagated, where the plugin keeps compiling and reads a
field the host never sends.
## Its first interface run found a live one
```
dashboard-interop.d.ts:67 TaskCardProps.workflowStepNameLookup is not a property of the real TaskCardProps
```
Git history says it **was** one when FN-2466 and FN-7039 added this
threading. The dashboard removed it later; nothing propagated that to
the plugin's hand-written declaration. So the plugin built a lookup map
from `context.workflowSteps` on every render, threaded it through two
components, and handed it to a `TaskCard` with no such prop.
Deleted rather than exempted — a new gate shouldn't ship with a waiver
for its own first finding. Behaviour-preserving: the value never reached
anything.
## Measured on `main`
| check | result |
|---|---|
| population | **7 functions + 10 interfaces across 6 plugins**, all
matching after the deletion |
| control probe | phantom property **caught**; clean tree exits 0 |
| anti-vacuity | now also requires a non-zero *interface* comparison |
| gate's own suite | **5 → 8** |
| dependency-graph suite | 179 green; `tsc` clean |
| other five gates · census | green |
## Running total for this check
Three real drifts, none of which any other instrument reported:
1. `isTaskStuck` stuck at three parameters through the whole lane
conversion (#3003)
2. `taskStuckTimeoutMs?: number` vs the required `number | undefined` —
in **two independent authors'** declarations
3. `workflowStepNameLookup` outliving its removal from `TaskCard`
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
ccf562f178