diff --git a/docs/work/conformance-system-v1/02-boot-assertions/_story.md b/docs/work/conformance-system-v1/02-boot-assertions/_story.md
new file mode 100644
index 0000000..3eb605b
--- /dev/null
+++ b/docs/work/conformance-system-v1/02-boot-assertions/_story.md
@@ -0,0 +1,65 @@
+---
+id: 02-boot-assertions
+epic: conformance-system-v1
+title: assertFeatureConformance + boot wiring
+type: technical-story
+status: done
+feature: core-shared
+depends-on: [01-define-feature-helper]
+blocks: [03-eslint-rules]
+---
+
+## Goal
+Runtime boot-time verification that every manifest-declared use case is bound
+through the brand-attaching wrappers. Each feature's `bindProductionX(ctx)`
+self-asserts at the tail; `pnpm dev` refuses to boot on drift.
+
+## Why
+Type casts can mask unwrapped factories; manifest edits can drift from
+binders without TypeScript noticing. Boot assertions catch what the type
+system can't see — at zero cost during the inner agent feedback loop, and
+synchronously at startup so failures fire loudly.
+
+## Done when
+- `withSpan`, `withCapture`, `withAudit` attach non-enumerable runtime markers
+  matching the type-level brand names
+- `assertFeatureConformance(container, manifest, symbols, ctx)` resolves each
+  manifest use case and throws `ConformanceError` on a missing brand
+- `auth.bindProductionAuth(ctx)` self-asserts at the tail
+- `pnpm dev` boots cleanly for the existing `auth` wiring; rebinding `signIn`
+  with an unwrapped factory causes `pnpm dev` to throw at startup
+
+## In scope
+- Runtime marker attachment via `Object.defineProperty(fn, "__brand", { … })`
+  (non-enumerable, non-writable, non-configurable)
+- `isInstrumented` / `isCaptured` / `isAudited` predicates
+- `ConformanceError` class (extends `Error`)
+- `assertFeatureConformance(container, manifest, symbols, ctx)` helper
+- Wiring into `packages/auth/src/di/bind-production.ts` (tail-of-binder
+  self-assertion)
+- `withAudit` upgraded from passthrough to a thin wrapper that attaches its
+  runtime brand without changing observable behaviour
+
+## Out of scope
+- `assertConformance` over a multi-feature container collection at the app's
+  `bindAll()` (current per-feature self-assertion is sufficient and
+  forward-compatible)
+- Wiring boot assertions into `cms` and `web-tanstack` — neither has a
+  `bind-production.ts` yet; they'll inherit the check whenever they grow one
+- Manifests for `blog`, `media`, `navigation`, `marketing-pages` (their
+  `bindProductionX` stays unchanged in this story)
+- Automated audit recording driven by manifest `audits[]` declarations
+  (deferred to a later story)
+
+## Tasks
+- [x] Re-export `authManifest` from auth root barrel
+- [x] TODO breadcrumb in `withAudit` pointing at future automation
+- [x] Runtime marker helpers (`attachBrand`, `isInstrumented`, `isCaptured`, `isAudited`)
+- [x] `withSpan` attaches runtime `__instrumented` marker
+- [x] `withCapture` attaches runtime `__captured` marker
+- [x] `withAudit` wraps + attaches runtime `__audited` marker
+- [x] `ConformanceError` class
+- [x] `assertFeatureConformance` helper + tests
+- [x] Conformance barrel + subpath exports updated
+- [x] `bindProductionAuth` self-asserts at the tail
+- [x] Final verification + story closeout
diff --git a/docs/work/conformance-system-v1/_epic.md b/docs/work/conformance-system-v1/_epic.md
index a5962fe..befb3d7 100644
--- a/docs/work/conformance-system-v1/_epic.md
+++ b/docs/work/conformance-system-v1/_epic.md
@@ -31,7 +31,7 @@ See `docs/architecture/feature-conformance-explainer.html` and
 
 ## Stories
 - [x] [01 — defineFeature helper + Instrumented/Captured/Audited brands](01-define-feature-helper/_story.md)
-- [ ] 02 — `assertConformance` + boot wiring (later plan)
+- [x] [02 — `assertFeatureConformance` + boot wiring](02-boot-assertions/_story.md)
 - [ ] 03 — AST-aware ESLint rules (later plan)
 - [ ] 04 — CI drift gate (later plan)
 - [ ] 05 — Generator emits manifest + contracts + test stubs (later plan)
diff --git a/packages/auth/src/di/bind-production.ts b/packages/auth/src/di/bind-production.ts
index 94d5868..b422fb0 100644
--- a/packages/auth/src/di/bind-production.ts
+++ b/packages/auth/src/di/bind-production.ts
@@ -6,7 +6,9 @@ import {
   type ILogger,
 } from "@repo/core-shared/instrumentation";
 import type { BindProductionContext } from "@repo/core-shared/di";
+import { assertFeatureConformance } from "@repo/core-shared/conformance";
 import type { ProductionUseCase } from "@repo/core-shared/conformance";
+import { authManifest } from "../feature.manifest";
 import type { AuthManifest } from "../feature.manifest";
 import type {
   SignInInput,
@@ -158,4 +160,17 @@ export function bindProductionAuth(ctx: BindProductionContext): void {
   // <gen:event-handlers>
   // <gen:jobs>
   // <gen:realtime-handlers>
+
+  // Boot-time conformance check: refuses to start if any use-case binding
+  // is missing a required brand (withSpan / withCapture / withAudit).
+  assertFeatureConformance(
+    authContainer,
+    authManifest,
+    {
+      signIn: AUTH_SYMBOLS.ISignInUseCase,
+      signUp: AUTH_SYMBOLS.ISignUpUseCase,
+      signOut: AUTH_SYMBOLS.ISignOutUseCase,
+    },
+    ctx,
+  );
 }
diff --git a/packages/auth/src/index.ts b/packages/auth/src/index.ts
index c067ff8..d400d0d 100644
--- a/packages/auth/src/index.ts
+++ b/packages/auth/src/index.ts
@@ -43,3 +43,8 @@ export {
   type UserSignedUpEvent,
 } from "./events/user-signed-up.event";
 // <gen:realtime-channels>
+
+// Feature conformance manifest (added in conformance milestone i, exposed
+// here in milestone ii so the boot-time assertion and future tooling can
+// read the contract from the package boundary).
+export { authManifest, type AuthManifest } from "./feature.manifest";
diff --git a/packages/core-audit/src/with-audit.chain.test.ts b/packages/core-audit/src/with-audit.chain.test.ts
new file mode 100644
index 0000000..232a2f3
--- /dev/null
+++ b/packages/core-audit/src/with-audit.chain.test.ts
@@ -0,0 +1,76 @@
+import { describe, it, expect, vi } from "vitest";
+import { withSpan } from "@repo/core-shared/instrumentation";
+import { withCapture } from "@repo/core-shared/instrumentation";
+import { isInstrumented, isCaptured, isAudited } from "@repo/core-shared/conformance";
+import { withAudit } from "@/with-audit";
+import type { IAuditLog } from "@/audit-log.interface";
+import type { ITracer, ISpan } from "@repo/core-shared/instrumentation";
+import type { ILogger } from "@repo/core-shared/instrumentation";
+
+function makeTracer(): ITracer {
+  return {
+    startSpan: vi.fn(async (_opts, fn) => {
+      const span: ISpan = { setAttribute: () => {}, setStatus: () => {} };
+      return fn(span);
+    }),
+  };
+}
+
+function makeLogger(): ILogger {
+  return {
+    captureException: vi.fn(),
+    captureMessage: vi.fn(),
+    addBreadcrumb: vi.fn(),
+    setUser: vi.fn(),
+  };
+}
+
+function makeAuditLog(): IAuditLog {
+  return {
+    record: vi.fn().mockResolvedValue(undefined),
+    eraseSubject: vi.fn().mockResolvedValue(undefined),
+  };
+}
+
+describe("brand propagation across the full wrapper chain", () => {
+  it("withSpan(withCapture(withAudit(fn))) carries all three brands on the outer wrapper", () => {
+    const tracer = makeTracer();
+    const logger = makeLogger();
+    const auditLog = makeAuditLog();
+    const fn = async (input: { id: string }) => ({ ok: true, id: input.id });
+
+    const wrapped = withSpan(
+      tracer,
+      { name: "test.chain", op: "use-case" },
+      withCapture(
+        logger,
+        { feature: "test", layer: "use-case" },
+        withAudit(auditLog, fn),
+      ),
+    );
+
+    expect(isInstrumented(wrapped)).toBe(true);
+    expect(isCaptured(wrapped)).toBe(true);
+    expect(isAudited(wrapped)).toBe(true);
+  });
+
+  it("the full chain preserves input/output behaviour end-to-end", async () => {
+    const tracer = makeTracer();
+    const logger = makeLogger();
+    const auditLog = makeAuditLog();
+    const fn = async (input: { id: string }) => ({ ok: true, id: input.id });
+
+    const wrapped = withSpan(
+      tracer,
+      { name: "test.chain", op: "use-case" },
+      withCapture(
+        logger,
+        { feature: "test", layer: "use-case" },
+        withAudit(auditLog, fn),
+      ),
+    );
+
+    const result = await wrapped({ id: "abc" });
+    expect(result).toEqual({ ok: true, id: "abc" });
+  });
+});
diff --git a/packages/core-audit/src/with-audit.test.ts b/packages/core-audit/src/with-audit.test.ts
index 0ab2e8b..731be28 100644
--- a/packages/core-audit/src/with-audit.test.ts
+++ b/packages/core-audit/src/with-audit.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, expectTypeOf, vi } from "vitest";
 import { withAudit, type Audited } from "@/with-audit";
 import type { IAuditLog } from "@/audit-log.interface";
+import { isAudited } from "@repo/core-shared/conformance";
 
 function makeAuditLog(): IAuditLog {
   return {
@@ -17,6 +18,22 @@ describe("withAudit", () => {
     expectTypeOf(wrapped).toMatchTypeOf<Audited<typeof fn>>();
   });
 
+  it("attaches __audited as a non-enumerable property on the wrapped function", () => {
+    const auditLog = makeAuditLog();
+    const fn = async () => ({ ok: true });
+    const wrapped = withAudit(auditLog, fn);
+    expect(isAudited(wrapped)).toBe(true);
+    expect(Object.keys(wrapped)).not.toContain("__audited");
+  });
+
+  it("does NOT pollute the original input function with the brand", () => {
+    const auditLog = makeAuditLog();
+    const fn = async () => ({ ok: true });
+    const wrapped = withAudit(auditLog, fn);
+    expect(isAudited(fn)).toBe(false);
+    expect(wrapped).not.toBe(fn);
+  });
+
   it("passes input and output through unchanged", async () => {
     const auditLog = makeAuditLog();
     const fn = async (input: { id: string }) => ({ ok: true, id: input.id });
diff --git a/packages/core-audit/src/with-audit.ts b/packages/core-audit/src/with-audit.ts
index a521816..89d0af7 100644
--- a/packages/core-audit/src/with-audit.ts
+++ b/packages/core-audit/src/with-audit.ts
@@ -1,34 +1,36 @@
 import type { IAuditLog } from "./audit-log.interface";
+import { attachBrand } from "@repo/core-shared/conformance";
 
 /**
  * Phantom-type brand attached at wrap time by `withAudit`. The conformance
  * system uses this as the type-level seam for mutating use cases that
  * declare `audits: [...]` in their manifest — without `__audited`, the
  * binding is not assignable to `ProductionUseCase<I, O, M>` when M demands
- * it.
+ * it. At runtime the brand is a non-enumerable property attached by
+ * `attachBrand` from `@repo/core-shared/conformance`, so the boot-time
+ * assertion can verify the binding went through the audit-aware path.
  */
 export type Audited<F> = F & { readonly __audited: true };
 
 /**
- * Use-case wrapper applied at DI bind time. In milestone i this is a
- * brand-only attachment: it does not yet automatically call `auditLog.record`.
- * Use cases continue to call `auditLog.record(...)` in their own bodies; the
- * wrapper exists to make "binding was bound through the audit-aware path"
- * type-checkable at compile time.
- *
- * A future story may move auditing logic out of factory bodies and into the
- * wrapper itself (driven by manifest declarations) — but that requires the
- * manifest's `audits[]` entries to fully specify what gets recorded, which
- * is out of scope here.
+ * Use-case wrapper applied at DI bind time. The wrapper is a thin closure
+ * that forwards to `fn` unchanged and carries the `__audited` brand. The
+ * forward closure (instead of returning `fn` directly) keeps the brand on
+ * a fresh function so the caller's original `fn` is not mutated — important
+ * when the same factory output is used elsewhere unwrapped (dev-seed paths,
+ * tests).
  */
 export function withAudit<Args extends unknown[], R>(
-  // The auditLog is part of the signature for two reasons: (1) callers must
-  // pass it at bind time, ensuring the dep is available, and (2) future
-  // versions of this wrapper will use it to emit audit events from the
-  // declarative manifest entry directly.
+  // TODO(conformance milestone iii+): wire automated recording from manifest
+  // `audits[]` declarations. For now, the wrapper exists to:
+  //   (1) require callers to pass the auditLog at bind time (dep is available)
+  //   (2) attach the `__audited` brand so the boot-time assertion can verify
+  //       mutating use cases were bound through the audit-aware path.
   auditLog: IAuditLog,
   fn: (...args: Args) => Promise<R>,
 ): Audited<(...args: Args) => Promise<R>> {
   void auditLog;
-  return fn as Audited<(...args: Args) => Promise<R>>;
+  const wrapped: (...args: Args) => Promise<R> = (...args) => fn(...args);
+  attachBrand(wrapped, "__audited");
+  return wrapped as Audited<(...args: Args) => Promise<R>>;
 }
diff --git a/packages/core-shared/src/conformance/assert-bindings.test.ts b/packages/core-shared/src/conformance/assert-bindings.test.ts
new file mode 100644
index 0000000..4d26263
--- /dev/null
+++ b/packages/core-shared/src/conformance/assert-bindings.test.ts
@@ -0,0 +1,210 @@
+import { describe, it, expect, vi } from "vitest";
+import "reflect-metadata";
+import { Container } from "inversify";
+import { defineFeature } from "@/conformance/define-feature";
+import { ConformanceError } from "@/conformance/conformance-error";
+import { assertFeatureConformance } from "@/conformance/assert-bindings";
+import { withSpan } from "@/instrumentation/with-span";
+import { withCapture } from "@/instrumentation/with-capture";
+import type { ITracer, ISpan } from "@/instrumentation/tracer.interface";
+import type { ILogger } from "@/instrumentation/logger.interface";
+import type { BindContext } from "@/di/bind-context";
+
+function makeTracer(): ITracer {
+  return {
+    startSpan: vi.fn(async (_opts, fn) => {
+      const span: ISpan = { setAttribute: () => {}, setStatus: () => {} };
+      return fn(span);
+    }),
+  };
+}
+
+function makeLogger(): ILogger {
+  return {
+    captureException: vi.fn(),
+    captureMessage: vi.fn(),
+    addBreadcrumb: vi.fn(),
+    setUser: vi.fn(),
+  };
+}
+
+function makeCtx(): BindContext {
+  return { tracer: makeTracer(), logger: makeLogger() };
+}
+
+describe("assertFeatureConformance", () => {
+  it("passes when every use case is bound through withSpan + withCapture", () => {
+    const container = new Container();
+    const sym = Symbol("test.signIn");
+    const ctx = makeCtx();
+    const bound = withSpan(
+      ctx.tracer,
+      { name: "test.signIn", op: "use-case" },
+      withCapture(ctx.logger, { feature: "test", layer: "use-case" }, async (x: number) => x + 1),
+    );
+    container.bind(sym).toConstantValue(bound);
+
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signIn: { mutates: false, audits: [], publishes: [], consumes: [] },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signIn: sym }, ctx),
+    ).not.toThrow();
+  });
+
+  it("throws when a use case binding is missing the __instrumented brand", () => {
+    const container = new Container();
+    const sym = Symbol("test.signIn");
+    const ctx = makeCtx();
+    const unwrapped = async (x: number) => x + 1;
+    container.bind(sym).toConstantValue(unwrapped);
+
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signIn: { mutates: false, audits: [], publishes: [], consumes: [] },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signIn: sym }, ctx),
+    ).toThrow(ConformanceError);
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signIn: sym }, ctx),
+    ).toThrow(/test\.signIn.*__instrumented/);
+  });
+
+  it("throws when a use case binding is missing the __captured brand", () => {
+    const container = new Container();
+    const sym = Symbol("test.signIn");
+    const ctx = makeCtx();
+    // withSpan-only — no withCapture wrap
+    const partial = withSpan(
+      ctx.tracer,
+      { name: "test.signIn", op: "use-case" },
+      async (x: number) => x + 1,
+    );
+    container.bind(sym).toConstantValue(partial);
+
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signIn: { mutates: false, audits: [], publishes: [], consumes: [] },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signIn: sym }, ctx),
+    ).toThrow(/__captured/);
+  });
+
+  it("throws when a mutating use case with audits is missing the __audited brand", () => {
+    const container = new Container();
+    const sym = Symbol("test.signUp");
+    const ctx = makeCtx();
+    const wrappedNoAudit = withSpan(
+      ctx.tracer,
+      { name: "test.signUp", op: "use-case" },
+      withCapture(ctx.logger, { feature: "test" }, async (x: number) => x + 1),
+    );
+    container.bind(sym).toConstantValue(wrappedNoAudit);
+
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signUp: {
+          mutates: true,
+          audits: ["user.created"],
+          publishes: [],
+          consumes: [],
+        },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signUp: sym }, ctx),
+    ).toThrow(/__audited/);
+  });
+
+  it("passes for a mutating use case with empty audits (no __audited required)", () => {
+    const container = new Container();
+    const sym = Symbol("test.signUp");
+    const ctx = makeCtx();
+    const wrappedNoAudit = withSpan(
+      ctx.tracer,
+      { name: "test.signUp", op: "use-case" },
+      withCapture(ctx.logger, { feature: "test" }, async (x: number) => x + 1),
+    );
+    container.bind(sym).toConstantValue(wrappedNoAudit);
+
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signUp: {
+          mutates: true,
+          audits: [],
+          publishes: [],
+          consumes: [],
+        },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signUp: sym }, ctx),
+    ).not.toThrow();
+  });
+
+  it("throws when no symbol is provided for a manifest use case", () => {
+    const container = new Container();
+    const ctx = makeCtx();
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signIn: { mutates: false, audits: [], publishes: [], consumes: [] },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+    expect(() => assertFeatureConformance(container, manifest, {}, ctx)).toThrow(
+      /no symbol provided/,
+    );
+  });
+
+  it("throws when the container cannot resolve the symbol", () => {
+    const container = new Container();
+    const sym = Symbol("test.signIn");
+    const ctx = makeCtx();
+    const manifest = defineFeature({
+      name: "test",
+      requiredCores: [],
+      useCases: {
+        signIn: { mutates: false, audits: [], publishes: [], consumes: [] },
+      },
+      realtimeChannels: [],
+      jobs: [],
+    } as const);
+    expect(() =>
+      assertFeatureConformance(container, manifest, { signIn: sym }, ctx),
+    ).toThrow(ConformanceError);
+  });
+});
diff --git a/packages/core-shared/src/conformance/assert-bindings.ts b/packages/core-shared/src/conformance/assert-bindings.ts
new file mode 100644
index 0000000..28fd7f7
--- /dev/null
+++ b/packages/core-shared/src/conformance/assert-bindings.ts
@@ -0,0 +1,62 @@
+import type { Container } from "inversify";
+import type { FeatureManifest } from "./define-feature";
+import { isInstrumented, isCaptured, isAudited } from "./brand-runtime";
+import { ConformanceError } from "./conformance-error";
+import type { BindContext } from "../di/bind-context";
+
+/**
+ * Runtime check that every manifest-declared use case is bound through the
+ * brand-attaching wrappers (`withSpan` → `__instrumented`,
+ * `withCapture` → `__captured`, `withAudit` → `__audited` when required).
+ *
+ * Called at the tail of each feature's `bindProductionX(ctx)` so:
+ *   - `pnpm dev` refuses to boot on drift (synchronous throw)
+ *   - The check runs once per feature, not per request
+ *   - Future apps that wire `bindProductionX` inherit the check for free
+ *
+ * The `symbols` map is declared inline by the feature's binder; the manifest
+ * holds the contract, the binder holds the container symbols. This keeps
+ * the manifest free of DI-coupling while letting each feature declare its
+ * own wiring keys.
+ */
+export function assertFeatureConformance(
+  container: Container,
+  manifest: FeatureManifest,
+  symbols: Record<string, symbol>,
+  _ctx: BindContext,
+): void {
+  void _ctx; // future: also check ctx.bus / ctx.auditLog presence vs requiredCores
+  for (const [name, useCase] of Object.entries(manifest.useCases)) {
+    const sym = symbols[name];
+    if (!sym) {
+      throw new ConformanceError(
+        `${manifest.name}.${name}: no symbol provided in symbols map`,
+      );
+    }
+    let bound: unknown;
+    try {
+      bound = container.get(sym);
+    } catch (cause) {
+      throw new ConformanceError(
+        `${manifest.name}.${name}: container could not resolve symbol (${String(cause)})`,
+      );
+    }
+    if (!isInstrumented(bound)) {
+      throw new ConformanceError(
+        `${manifest.name}.${name}: missing __instrumented brand — was withSpan applied at bind time?`,
+      );
+    }
+    if (!isCaptured(bound)) {
+      throw new ConformanceError(
+        `${manifest.name}.${name}: missing __captured brand — was withCapture applied at bind time?`,
+      );
+    }
+    if (useCase.mutates && useCase.audits.length > 0) {
+      if (!isAudited(bound)) {
+        throw new ConformanceError(
+          `${manifest.name}.${name}: declares audits but binding is missing __audited brand — was withAudit applied at bind time?`,
+        );
+      }
+    }
+  }
+}
diff --git a/packages/core-shared/src/conformance/brand-runtime.test.ts b/packages/core-shared/src/conformance/brand-runtime.test.ts
new file mode 100644
index 0000000..f106b8f
--- /dev/null
+++ b/packages/core-shared/src/conformance/brand-runtime.test.ts
@@ -0,0 +1,71 @@
+import { describe, it, expect } from "vitest";
+import {
+  attachBrand,
+  isInstrumented,
+  isCaptured,
+  isAudited,
+} from "@/conformance/brand-runtime";
+
+describe("brand-runtime", () => {
+  it("attachBrand adds a non-enumerable property and returns the same reference", () => {
+    const fn = () => {};
+    const result = attachBrand(fn, "__instrumented");
+    expect(result).toBe(fn);
+    expect(isInstrumented(fn)).toBe(true);
+    // Non-enumerable: must not show up in Object.keys
+    expect(Object.keys(fn)).not.toContain("__instrumented");
+  });
+
+  it("predicates return false for unwrapped functions", () => {
+    const fn = () => {};
+    expect(isInstrumented(fn)).toBe(false);
+    expect(isCaptured(fn)).toBe(false);
+    expect(isAudited(fn)).toBe(false);
+  });
+
+  it("predicates discriminate between brands", () => {
+    const instrumented = () => {};
+    attachBrand(instrumented, "__instrumented");
+    expect(isInstrumented(instrumented)).toBe(true);
+    expect(isCaptured(instrumented)).toBe(false);
+    expect(isAudited(instrumented)).toBe(false);
+
+    const captured = () => {};
+    attachBrand(captured, "__captured");
+    expect(isInstrumented(captured)).toBe(false);
+    expect(isCaptured(captured)).toBe(true);
+    expect(isAudited(captured)).toBe(false);
+
+    const audited = () => {};
+    attachBrand(audited, "__audited");
+    expect(isAudited(audited)).toBe(true);
+  });
+
+  it("composing brands stacks them on the same function", () => {
+    const fn = () => {};
+    attachBrand(fn, "__instrumented");
+    attachBrand(fn, "__captured");
+    attachBrand(fn, "__audited");
+    expect(isInstrumented(fn)).toBe(true);
+    expect(isCaptured(fn)).toBe(true);
+    expect(isAudited(fn)).toBe(true);
+  });
+
+  it("attached brands are non-writable and non-configurable", () => {
+    const fn = () => {};
+    attachBrand(fn, "__instrumented");
+    const desc = Object.getOwnPropertyDescriptor(fn, "__instrumented");
+    expect(desc?.writable).toBe(false);
+    expect(desc?.configurable).toBe(false);
+    expect(desc?.enumerable).toBe(false);
+    expect(desc?.value).toBe(true);
+  });
+
+  it("predicates return false for non-function inputs", () => {
+    expect(isInstrumented(null)).toBe(false);
+    expect(isInstrumented(undefined)).toBe(false);
+    expect(isInstrumented(42)).toBe(false);
+    expect(isInstrumented("string")).toBe(false);
+    expect(isInstrumented({})).toBe(false);
+  });
+});
diff --git a/packages/core-shared/src/conformance/brand-runtime.ts b/packages/core-shared/src/conformance/brand-runtime.ts
new file mode 100644
index 0000000..c378fe5
--- /dev/null
+++ b/packages/core-shared/src/conformance/brand-runtime.ts
@@ -0,0 +1,53 @@
+/**
+ * Runtime brand attachment + predicates. The companion to the phantom-type
+ * brands defined in `./brands.ts`: at compile time the brand is a structural
+ * intersection; at runtime it is a non-enumerable, non-writable,
+ * non-configurable property with the same name.
+ *
+ * Why non-enumerable: a wrapped function should not leak the marker through
+ * `Object.keys`, `JSON.stringify`, `for…in`, or spread. The marker only
+ * shows up to explicit lookups via `Reflect.has` or direct property access.
+ *
+ * Why non-writable + non-configurable: the marker is meant to be permanent
+ * once attached. The wrapper is the only caller; the marker is a one-shot
+ * commitment, not a mutable flag.
+ */
+
+type Brand = "__instrumented" | "__captured" | "__audited";
+
+/**
+ * Attaches the brand as a non-enumerable property on the given function.
+ * Returns the same reference (no allocation). Calling twice with the same
+ * brand on the same fn is a no-op (matching descriptors) — the engine silently
+ * accepts a redundant `defineProperty` call when every descriptor attribute
+ * matches the existing one. Redefining with different attributes (e.g. flipping
+ * `configurable`) would throw, but wrappers never do that.
+ */
+export function attachBrand<F extends object>(fn: F, brand: Brand): F {
+  Object.defineProperty(fn, brand, {
+    value: true,
+    enumerable: false,
+    writable: false,
+    configurable: false,
+  });
+  return fn;
+}
+
+function hasBrand(fn: unknown, brand: Brand): boolean {
+  if (typeof fn !== "function" && (typeof fn !== "object" || fn === null)) {
+    return false;
+  }
+  return (fn as Record<string, unknown>)[brand] === true;
+}
+
+export function isInstrumented(fn: unknown): boolean {
+  return hasBrand(fn, "__instrumented");
+}
+
+export function isCaptured(fn: unknown): boolean {
+  return hasBrand(fn, "__captured");
+}
+
+export function isAudited(fn: unknown): boolean {
+  return hasBrand(fn, "__audited");
+}
diff --git a/packages/core-shared/src/conformance/brands.ts b/packages/core-shared/src/conformance/brands.ts
index eeb1045..4ff9fe3 100644
--- a/packages/core-shared/src/conformance/brands.ts
+++ b/packages/core-shared/src/conformance/brands.ts
@@ -1,9 +1,11 @@
 /**
  * Phantom-type brands attached at wrap time by `withSpan`, `withCapture`,
- * and `withAudit`. Pure type-level — no runtime cost, no proxy, no
- * `Object.assign`. The conformance system uses these as the type-level
- * seam the binding signature checks; a use-case factory that hasn't been
- * wrapped is not assignable to a `ProductionUseCase<...>` slot.
+ * and `withAudit`. The brand has a type-level form (this file) and a
+ * non-enumerable runtime counterpart (see `./brand-runtime.ts`). The runtime
+ * cost is one `Object.defineProperty` call per wrap. The conformance system
+ * uses these as the type-level seam the binding signature checks; a use-case
+ * factory that hasn't been wrapped is not assignable to a
+ * `ProductionUseCase<...>` slot.
  */
 export type Instrumented<F> = F & { readonly __instrumented: true };
 export type Captured<F> = F & { readonly __captured: true };
diff --git a/packages/core-shared/src/conformance/conformance-error.test.ts b/packages/core-shared/src/conformance/conformance-error.test.ts
new file mode 100644
index 0000000..4d4eb46
--- /dev/null
+++ b/packages/core-shared/src/conformance/conformance-error.test.ts
@@ -0,0 +1,17 @@
+import { describe, it, expect } from "vitest";
+import { ConformanceError } from "@/conformance/conformance-error";
+
+describe("ConformanceError", () => {
+  it("extends Error with the standard shape", () => {
+    const err = new ConformanceError("auth.signIn: missing __instrumented brand");
+    expect(err).toBeInstanceOf(Error);
+    expect(err).toBeInstanceOf(ConformanceError);
+    expect(err.message).toBe("auth.signIn: missing __instrumented brand");
+    expect(err.name).toBe("ConformanceError");
+  });
+
+  it("preserves a stack trace", () => {
+    const err = new ConformanceError("test");
+    expect(typeof err.stack).toBe("string");
+  });
+});
diff --git a/packages/core-shared/src/conformance/conformance-error.ts b/packages/core-shared/src/conformance/conformance-error.ts
new file mode 100644
index 0000000..4683262
--- /dev/null
+++ b/packages/core-shared/src/conformance/conformance-error.ts
@@ -0,0 +1,13 @@
+/**
+ * Thrown by `assertFeatureConformance` when a binding does not match the
+ * manifest's declared shape. The boot assertion lets this propagate
+ * synchronously so `pnpm dev` refuses to start on drift.
+ */
+export class ConformanceError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "ConformanceError";
+    // Maintain a proper prototype chain across down-compilation.
+    Object.setPrototypeOf(this, ConformanceError.prototype);
+  }
+}
diff --git a/packages/core-shared/src/conformance/index.ts b/packages/core-shared/src/conformance/index.ts
index 773dc64..13bcf94 100644
--- a/packages/core-shared/src/conformance/index.ts
+++ b/packages/core-shared/src/conformance/index.ts
@@ -2,3 +2,11 @@ export type { Instrumented, Captured } from "./brands";
 export type { FeatureManifest, UseCaseManifest } from "./define-feature";
 export { defineFeature } from "./define-feature";
 export type { ProductionUseCase } from "./production-use-case";
+export {
+  attachBrand,
+  isInstrumented,
+  isCaptured,
+  isAudited,
+} from "./brand-runtime";
+export { ConformanceError } from "./conformance-error";
+export { assertFeatureConformance } from "./assert-bindings";
diff --git a/packages/core-shared/src/instrumentation/with-capture.test.ts b/packages/core-shared/src/instrumentation/with-capture.test.ts
index 28b4803..179534f 100644
--- a/packages/core-shared/src/instrumentation/with-capture.test.ts
+++ b/packages/core-shared/src/instrumentation/with-capture.test.ts
@@ -3,6 +3,7 @@ import { withCapture } from "@/instrumentation/with-capture";
 import type { ILogger } from "@/instrumentation/logger.interface";
 import { isReported } from "@/instrumentation/reported-flag";
 import type { Captured } from "@/conformance/brands";
+import { isCaptured } from "@/conformance/brand-runtime";
 
 function makeLogger(): ILogger & { captureException: ReturnType<typeof vi.fn> } {
   return {
@@ -70,3 +71,13 @@ describe("withCapture — brand", () => {
     expectTypeOf(wrapped).toMatchTypeOf<Captured<typeof fn>>();
   });
 });
+
+describe("withCapture — runtime brand", () => {
+  it("attaches __captured as a non-enumerable property on the wrapped function", async () => {
+    const logger = makeLogger();
+    const fn = async (a: number) => a + 1;
+    const wrapped = withCapture(logger, { layer: "use-case" }, fn);
+    expect(isCaptured(wrapped)).toBe(true);
+    expect(Object.keys(wrapped)).not.toContain("__captured");
+  });
+});
diff --git a/packages/core-shared/src/instrumentation/with-capture.ts b/packages/core-shared/src/instrumentation/with-capture.ts
index ed17420..8652115 100644
--- a/packages/core-shared/src/instrumentation/with-capture.ts
+++ b/packages/core-shared/src/instrumentation/with-capture.ts
@@ -1,5 +1,6 @@
 import type { ILogger } from "./logger.interface";
 import type { Captured } from "../conformance/brands";
+import { attachBrand } from "../conformance/brand-runtime";
 import { isReported, markReported } from "./reported-flag";
 
 /**
@@ -27,6 +28,8 @@ export function withCapture<Args extends unknown[], R>(
   tags: Record<string, string>,
   fn: (...args: Args) => Promise<R>,
 ): Captured<(...args: Args) => Promise<R>> {
+  const PROPAGATED_BRANDS = ["__instrumented", "__audited"] as const;
+
   const wrapped: (...args: Args) => Promise<R> = async (...args) => {
     try {
       return await fn(...args);
@@ -38,5 +41,14 @@ export function withCapture<Args extends unknown[], R>(
       throw err;
     }
   };
+  // Propagate brands from the inner function (e.g. __audited from withAudit,
+  // __instrumented if already spanned) so the outermost binding carries all brands.
+  // __captured is omitted here because it is attached explicitly below.
+  for (const brand of PROPAGATED_BRANDS) {
+    if ((fn as unknown as Record<string, unknown>)[brand] === true) {
+      attachBrand(wrapped, brand);
+    }
+  }
+  attachBrand(wrapped, "__captured");
   return wrapped as Captured<(...args: Args) => Promise<R>>;
 }
diff --git a/packages/core-shared/src/instrumentation/with-span.test.ts b/packages/core-shared/src/instrumentation/with-span.test.ts
index 91ccac4..1667cbd 100644
--- a/packages/core-shared/src/instrumentation/with-span.test.ts
+++ b/packages/core-shared/src/instrumentation/with-span.test.ts
@@ -2,6 +2,7 @@ import { describe, it, expect, expectTypeOf, vi } from "vitest";
 import { withSpan } from "@/instrumentation/with-span";
 import type { ITracer, ISpan, SpanOpts } from "@/instrumentation/tracer.interface";
 import type { Instrumented } from "@/conformance/brands";
+import { isInstrumented } from "@/conformance/brand-runtime";
 
 function makeRecordingTracer() {
   const calls: SpanOpts[] = [];
@@ -70,3 +71,13 @@ describe("withSpan — brand", () => {
     expectTypeOf(wrapped).toMatchTypeOf<Instrumented<typeof fn>>();
   });
 });
+
+describe("withSpan — runtime brand", () => {
+  it("attaches __instrumented as a non-enumerable property on the wrapped function", async () => {
+    const { tracer } = makeRecordingTracer();
+    const fn = async (a: number) => a + 1;
+    const wrapped = withSpan(tracer, { name: "test.brand", op: "use-case" }, fn);
+    expect(isInstrumented(wrapped)).toBe(true);
+    expect(Object.keys(wrapped)).not.toContain("__instrumented");
+  });
+});
diff --git a/packages/core-shared/src/instrumentation/with-span.ts b/packages/core-shared/src/instrumentation/with-span.ts
index 0685b0c..1e00da1 100644
--- a/packages/core-shared/src/instrumentation/with-span.ts
+++ b/packages/core-shared/src/instrumentation/with-span.ts
@@ -1,5 +1,8 @@
 import type { ITracer, SpanOpts } from "./tracer.interface";
 import type { Instrumented } from "../conformance/brands";
+import { attachBrand } from "../conformance/brand-runtime";
+
+const PROPAGATED_BRANDS = ["__captured", "__audited"] as const;
 
 export function withSpan<Args extends unknown[], R, Extra extends object>(
   tracer: ITracer,
@@ -20,7 +23,17 @@ export function withSpan<Args extends unknown[], R>(
     const resolved = typeof opts === "function" ? opts(args) : opts;
     return tracer.startSpan(resolved, () => fn(...args));
   };
-  // Cast is the only runtime concession — the brand is a phantom type;
-  // there is no real `__instrumented` property at runtime.
+  attachBrand(wrapped, "__instrumented");
+  // Propagate brands from the inner function (e.g. __captured from withCapture,
+  // __audited from withAudit) so the outermost binding carries all brands.
+  // withSpan is always outermost — the assertFeatureConformance check reads the
+  // container-resolved value (the withSpan result), so brands must be visible here.
+  for (const brand of PROPAGATED_BRANDS) {
+    if ((fn as unknown as Record<string, unknown>)[brand] === true) {
+      attachBrand(wrapped, brand);
+    }
+  }
+  // Cast is the type-level concession — the brand is now also a non-enumerable
+  // runtime property attached above by `attachBrand`.
   return wrapped as Instrumented<(...args: Args) => Promise<R>>;
 }