diff --git a/src/runtime/supervise/budget-floor.ts b/src/runtime/supervise/budget-floor.ts
index ef99f9b1..208b24aa 100644
--- a/src/runtime/supervise/budget-floor.ts
+++ b/src/runtime/supervise/budget-floor.ts
@@ -48,8 +48,12 @@ export const WORKER_TOKEN_FLOOR = {
  *
  * A `null` harness is the router/inline arm: it holds only coordination verbs and re-sends no
  * harness scaffolding, so it has no floor of this kind.
+ *
+ * Accepts a bare `string` because `AgentProfile.harness` is not exactly `BackendType` — an
+ * unrecognised name resolves to `null` (no floor) rather than throwing, which keeps an unknown
+ * harness admissible instead of refusing work on a name this table has not heard of.
  */
-export function workerTokenFloor(harness: BackendType | null): number | null {
-  if (harness === null) return null
+export function workerTokenFloor(harness: BackendType | string | null | undefined): number | null {
+  if (harness === null || harness === undefined) return null
   return (WORKER_TOKEN_FLOOR as Record<string, number | null>)[harness] ?? null
 }
diff --git a/src/runtime/supervise/scope.ts b/src/runtime/supervise/scope.ts
index e9d65e0e..acfbcf80 100644
--- a/src/runtime/supervise/scope.ts
+++ b/src/runtime/supervise/scope.ts
@@ -564,7 +564,13 @@ export function createScope<Out>(args: ScopeArgs): Scope<Out> {
       // `budget-exhausted` invites a caller to retry SMALLER, which here is the exact wrong move.
       // Checked after resolution because that is where the harness is known, and refunded the way
       // every sibling failure on this path is.
-      const floor = workerTokenFloor(spec.harness)
+      // `spec.harness` is null whenever the harness rides in the backend config instead of the
+      // spec — which is the path that actually spawns workers through the bridge. Reading only it
+      // made this guard miss the case it was written for: a root authored a 6,000-token child
+      // against a measured 31,211 floor, the guard never fired, and the child died having produced
+      // nothing (discovery-lab run proof-bridge-20260801f). The AgentProfile is where a root
+      // declares its child's harness, so it is the more reliable of the two.
+      const floor = workerTokenFloor(spec.harness ?? spec.profile.harness ?? null)
       if (floor !== null && opts.budget.maxTokens < floor) {
         args.pool.reconcile(reservation.ticket, zeroSpend())
         permit.release()
diff --git a/tests/kernel/budget-floor.test.ts b/tests/kernel/budget-floor.test.ts
index 2ad5a495..b1ac52d6 100644
--- a/tests/kernel/budget-floor.test.ts
+++ b/tests/kernel/budget-floor.test.ts
@@ -45,3 +45,25 @@ describe('worker token floor', () => {
     }
   })
 })
+
+describe('the floor reads the harness a root actually declared', () => {
+  // The guard originally read only `spec.harness`, which is null whenever the harness rides in the
+  // backend config rather than the spec — the path that actually spawns workers through the
+  // bridge. So it missed the case it exists for: run proof-bridge-20260801f authored a
+  // 6,000-token child against a 31,211 floor, admitted it, and the child produced nothing.
+  it('resolves a floor from an AgentProfile harness when the spec carries none', () => {
+    const specHarness = null
+    const profileHarness = 'pi' as const
+    expect(workerTokenFloor(specHarness ?? profileHarness)).toBe(31_211)
+  })
+
+  it('still has no floor when neither names a harness (router/inline arm)', () => {
+    const specHarness = null
+    const profileHarness = null
+    expect(workerTokenFloor(specHarness ?? profileHarness)).toBeNull()
+  })
+
+  it('refuses the exact budget that slipped through', () => {
+    expect(6_000).toBeLessThan(workerTokenFloor('pi')!)
+  })
+})