diff --git a/packages/effect-readiness/src/AwaitCondition.schema.ts b/packages/effect-readiness/src/AwaitCondition.schema.ts
index 24277c8..5131891 100644
--- a/packages/effect-readiness/src/AwaitCondition.schema.ts
+++ b/packages/effect-readiness/src/AwaitCondition.schema.ts
@@ -2,7 +2,9 @@ import { Schema } from 'effect'
 import { Condition } from './Condition.schema.js'
 import { ProbeTarget } from './ProbeTarget.schema.js'
 
-export class AwaitCondition extends Schema.TaggedClass<AwaitCondition>()('AwaitCondition', {
-  target: ProbeTarget,
-  condition: Condition,
-}) {}
+export class AwaitCondition
+  extends Schema.TaggedClass<AwaitCondition, { readonly brand: unique symbol }>()('AwaitCondition', {
+    target: ProbeTarget,
+    condition: Condition,
+  })
+{}
diff --git a/packages/effect-readiness/src/ProbeVerdict.schema.ts b/packages/effect-readiness/src/ProbeVerdict.schema.ts
index 7ade186..60887f8 100644
--- a/packages/effect-readiness/src/ProbeVerdict.schema.ts
+++ b/packages/effect-readiness/src/ProbeVerdict.schema.ts
@@ -8,12 +8,12 @@ type ProbeVerdictTypeId = typeof ProbeVerdictTypeId
  * `awaitCondition` hands back when the wait ends. One class, so the per-pass decision's
  * success variant and the public result are the same value.
  */
-export class Satisfied extends Schema.TaggedClass<Satisfied>()('Satisfied', {}) {
+export class Satisfied extends Schema.TaggedClass<Satisfied, { readonly brand: unique symbol }>()('Satisfied', {}) {
   readonly [ProbeVerdictTypeId] = ProbeVerdictTypeId
 }
 
 /** One pass's judgement that the condition does not hold yet; the shell polls again. */
-export class NotYet extends Schema.TaggedClass<NotYet>()('NotYet', {}) {
+export class NotYet extends Schema.TaggedClass<NotYet, { readonly brand: unique symbol }>()('NotYet', {}) {
   readonly [ProbeVerdictTypeId] = ProbeVerdictTypeId
 }
 
diff --git a/packages/effect-readiness/src/ReadinessError.schema.ts b/packages/effect-readiness/src/ReadinessError.schema.ts
index 6913917..70b24de 100644
--- a/packages/effect-readiness/src/ReadinessError.schema.ts
+++ b/packages/effect-readiness/src/ReadinessError.schema.ts
@@ -1,18 +1,22 @@
 import { Schema } from 'effect'
 
-export class LogSourceError extends Schema.TaggedError<LogSourceError>()('LogSourceError', {
-  source: Schema.String,
-  cause: Schema.optional(Schema.Unknown),
-}) {
+export class LogSourceError
+  extends Schema.TaggedError<LogSourceError, { readonly brand: unique symbol }>()('LogSourceError', {
+    source: Schema.String,
+    cause: Schema.optional(Schema.Unknown),
+  })
+{
   override get message(): string {
     return `log source "${this.source}" failed`
   }
 }
 
 /** A probe command failed to decode; the wait's own read built it, so this is a defect it surfaces. */
-export class ProbeInputInvalid extends Schema.TaggedError<ProbeInputInvalid>()('ProbeInputInvalid', {
-  issue: Schema.String,
-}) {
+export class ProbeInputInvalid
+  extends Schema.TaggedError<ProbeInputInvalid, { readonly brand: unique symbol }>()('ProbeInputInvalid', {
+    issue: Schema.String,
+  })
+{
   override get message(): string {
     return `The probe command did not decode: ${this.issue}`
   }
diff --git a/packages/effect-readiness/src/evaluate-probe.workflow.ts b/packages/effect-readiness/src/evaluate-probe.workflow.ts
index 505278d..339ec1c 100644
--- a/packages/effect-readiness/src/evaluate-probe.workflow.ts
+++ b/packages/effect-readiness/src/evaluate-probe.workflow.ts
@@ -5,10 +5,12 @@ import { Condition } from './Condition.schema.js'
 import { ProbeEvidence } from './ProbeEvidence.schema.js'
 import { NotYet, ProbeVerdict, Satisfied } from './ProbeVerdict.schema.js'
 
-export class EvaluateProbe extends Schema.TaggedClass<EvaluateProbe>()('EvaluateProbe', {
-  condition: Condition,
-  evidence: ProbeEvidence,
-}) {
+export class EvaluateProbe
+  extends Schema.TaggedClass<EvaluateProbe, { readonly brand: unique symbol }>()('EvaluateProbe', {
+    condition: Condition,
+    evidence: ProbeEvidence,
+  })
+{
   static readonly [Workflow.InstrumentationBrand] = {} as const
 }
 
diff --git a/packages/effect-readiness/src/resolve-probe.workflow.ts b/packages/effect-readiness/src/resolve-probe.workflow.ts
index 4c5df7f..9be120a 100644
--- a/packages/effect-readiness/src/resolve-probe.workflow.ts
+++ b/packages/effect-readiness/src/resolve-probe.workflow.ts
@@ -9,17 +9,21 @@ const ProbePlanTypeId: unique symbol = Symbol.for('@systemfsoftware/effect-readi
 type ProbePlanTypeId = typeof ProbePlanTypeId
 
 /** The condition names a port with no binding behind it; no host probe runs. */
-export class ProbeAbsent extends Schema.TaggedClass<ProbeAbsent>()('ProbeAbsent', { guestPort: Schema.Int }) {
+export class ProbeAbsent
+  extends Schema.TaggedClass<ProbeAbsent, { readonly brand: unique symbol }>()('ProbeAbsent', { guestPort: Schema.Int })
+{
   readonly [ProbePlanTypeId] = ProbePlanTypeId
 }
 
 /** The condition dials the bound host socket. */
-export class ProbeTcp extends Schema.TaggedClass<ProbeTcp>()('ProbeTcp', { binding: PortBinding }) {
+export class ProbeTcp
+  extends Schema.TaggedClass<ProbeTcp, { readonly brand: unique symbol }>()('ProbeTcp', { binding: PortBinding })
+{
   readonly [ProbePlanTypeId] = ProbePlanTypeId
 }
 
 /** The condition exchanges an HTTP request over the bound host socket. */
-export class ProbeHttp extends Schema.TaggedClass<ProbeHttp>()('ProbeHttp', {
+export class ProbeHttp extends Schema.TaggedClass<ProbeHttp, { readonly brand: unique symbol }>()('ProbeHttp', {
   binding: PortBinding,
   path: Schema.String,
 }) {
@@ -27,7 +31,9 @@ export class ProbeHttp extends Schema.TaggedClass<ProbeHttp>()('ProbeHttp', {
 }
 
 /** The condition reads the guest log stream for a pattern. */
-export class ProbeLog extends Schema.TaggedClass<ProbeLog>()('ProbeLog', { pattern: Schema.String }) {
+export class ProbeLog
+  extends Schema.TaggedClass<ProbeLog, { readonly brand: unique symbol }>()('ProbeLog', { pattern: Schema.String })
+{
   readonly [ProbePlanTypeId] = ProbePlanTypeId
 }
 
@@ -35,10 +41,12 @@ export class ProbeLog extends Schema.TaggedClass<ProbeLog>()('ProbeLog', { patte
 export const ProbePlan = Schema.Union([ProbeAbsent, ProbeTcp, ProbeHttp, ProbeLog])
 export type ProbePlan = typeof ProbePlan.Type
 
-export class ResolveProbe extends Schema.TaggedClass<ResolveProbe>()('ResolveProbe', {
-  target: ProbeTarget,
-  condition: Condition,
-}) {
+export class ResolveProbe
+  extends Schema.TaggedClass<ResolveProbe, { readonly brand: unique symbol }>()('ResolveProbe', {
+    target: ProbeTarget,
+    condition: Condition,
+  })
+{
   static readonly [Workflow.InstrumentationBrand] = {} as const
 }
 
diff --git a/packages/effect-readiness/tests/__fixtures__/loopback-service.fixture.ts b/packages/effect-readiness/tests/__fixtures__/loopback-service.fixture.ts
index 1e5633b..63a72d7 100644
--- a/packages/effect-readiness/tests/__fixtures__/loopback-service.fixture.ts
+++ b/packages/effect-readiness/tests/__fixtures__/loopback-service.fixture.ts
@@ -17,9 +17,11 @@ export interface LoopbackService {
 }
 
 /** The release probe fails with this when a stopped probe still holds a server connection. */
-export class ConnectionLeak extends Schema.TaggedError<ConnectionLeak>()('ConnectionLeak', {
-  open: Schema.Int,
-}) {}
+export class ConnectionLeak
+  extends Schema.TaggedError<ConnectionLeak, { readonly brand: unique symbol }>()('ConnectionLeak', {
+    open: Schema.Int,
+  })
+{}
 
 const zeroOpenConnections = (open: () => number): Effect.Effect<void, ConnectionLeak> =>
   Effect.repeat(