diff --git a/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.spec.ts b/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.spec.ts
new file mode 100644
index 000000000..bfa6764b7
--- /dev/null
+++ b/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.spec.ts
@@ -0,0 +1,212 @@
+import { StalkerChallengeRegistry } from './stalker-challenge-registry';
+
+describe('StalkerChallengeRegistry', () => {
+    let now: number;
+    let registry: StalkerChallengeRegistry;
+
+    beforeEach(() => {
+        now = Date.parse('2026-07-27T12:00:00.000Z');
+        registry = new StalkerChallengeRegistry({ now: () => now });
+    });
+
+    it('creates cryptographically opaque origin and credential references', () => {
+        const originRef = registry.issue(41, 'attempt-secret', {
+            finalOrigin: 'https://redirect.example',
+            kind: 'origin-approval',
+            landingPath: '/customer/c/',
+            sourceOrigin: 'https://source.example',
+        });
+        const credentialRef = registry.issue(41, 'attempt-secret', {
+            attemptNumber: 1,
+            constrainedUsername: 'account-secret',
+            kind: 'credentials',
+        });
+
+        expect(originRef).toMatch(/^[A-Za-z0-9_-]{43}$/);
+        expect(credentialRef).toMatch(/^[A-Za-z0-9_-]{43}$/);
+        expect(originRef).not.toBe(credentialRef);
+        for (const fragment of [
+            '41',
+            'attempt',
+            'redirect',
+            'customer',
+            'account',
+        ]) {
+            expect(originRef).not.toContain(fragment);
+            expect(credentialRef).not.toContain(fragment);
+        }
+    });
+
+    it('binds a challenge to its renderer without letting a foreign renderer consume it', () => {
+        const ref = registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 42,
+            })
+        ).toEqual({ kind: 'invalid' });
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 41,
+            })
+        ).toEqual({
+            challenge: {
+                attemptNumber: 1,
+                kind: 'credentials',
+            },
+            kind: 'consumed',
+        });
+    });
+
+    it('binds a challenge to its exact connection attempt', () => {
+        const ref = registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-b',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 41,
+            })
+        ).toEqual({ kind: 'invalid' });
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 41,
+            }).kind
+        ).toBe('consumed');
+    });
+
+    it('requires the response kind issued for the challenge', () => {
+        const ref = registry.issue(41, 'attempt-a', {
+            finalOrigin: 'https://redirect.example',
+            kind: 'origin-approval',
+            landingPath: '/c/',
+            sourceOrigin: 'https://source.example',
+        });
+
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 41,
+            })
+        ).toEqual({ kind: 'invalid' });
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'origin-approval',
+                senderId: 41,
+            }).kind
+        ).toBe('consumed');
+    });
+
+    it('consumes a challenge exactly once', () => {
+        const ref = registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+        const request = {
+            attemptRef: 'attempt-a',
+            challengeRef: ref,
+            responseKind: 'credentials' as const,
+            senderId: 41,
+        };
+
+        expect(registry.consume(request).kind).toBe('consumed');
+        expect(registry.consume(request)).toEqual({ kind: 'invalid' });
+    });
+
+    it('expires a challenge after two minutes using the injected clock', () => {
+        const ref = registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        now += 120_000;
+
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: ref,
+                responseKind: 'credentials',
+                senderId: 41,
+            })
+        ).toEqual({ kind: 'invalid' });
+        expect(registry.size).toBe(0);
+    });
+
+    it('invalidates every challenge when an attempt terminates', () => {
+        const first = registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+        registry.issue(41, 'attempt-a', {
+            finalOrigin: 'https://redirect.example',
+            kind: 'origin-approval',
+            landingPath: '/c/',
+            sourceOrigin: 'https://source.example',
+        });
+        registry.issue(41, 'attempt-b', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        registry.invalidateAttempt(41, 'attempt-a');
+
+        expect(
+            registry.consume({
+                attemptRef: 'attempt-a',
+                challengeRef: first,
+                responseKind: 'credentials',
+                senderId: 41,
+            })
+        ).toEqual({ kind: 'invalid' });
+        expect(registry.size).toBe(1);
+    });
+
+    it('invalidates all challenges owned by a destroyed renderer', () => {
+        registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+        registry.issue(41, 'attempt-b', {
+            attemptNumber: 2,
+            kind: 'credentials',
+        });
+        registry.issue(42, 'attempt-c', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        registry.invalidateSender(41);
+
+        expect(registry.size).toBe(1);
+    });
+
+    it('does not expose enumerable challenge state', () => {
+        registry.issue(41, 'attempt-a', {
+            attemptNumber: 1,
+            kind: 'credentials',
+        });
+
+        expect(JSON.stringify(registry)).toBe('{}');
+        expect(Object.keys(registry)).toEqual([]);
+    });
+});
diff --git a/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.ts b/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.ts
new file mode 100644
index 000000000..c482200c0
--- /dev/null
+++ b/apps/electron-backend/src/app/services/stalker-session/stalker-challenge-registry.ts
@@ -0,0 +1,253 @@
+import { randomBytes } from 'node:crypto';
+
+const CHALLENGE_TTL_MS = 120_000;
+const CHALLENGE_RANDOM_BYTES = 32;
+const MAX_ACTIVE_CHALLENGES = 4_096;
+const MAX_REFERENCE_GENERATION_ATTEMPTS = 4;
+
+export interface StalkerOriginApprovalChallenge {
+    kind: 'origin-approval';
+    sourceOrigin: string;
+    finalOrigin: string;
+    landingPath: string;
+}
+
+export interface StalkerCredentialsChallenge {
+    kind: 'credentials';
+    attemptNumber: number;
+    constrainedUsername?: string;
+    savedCredentialsRejected?: boolean;
+}
+
+export type StalkerChallenge =
+    | StalkerOriginApprovalChallenge
+    | StalkerCredentialsChallenge;
+
+export interface StalkerChallengeConsumeRequest {
+    senderId: number;
+    attemptRef: string;
+    challengeRef: string;
+    responseKind: StalkerChallenge['kind'];
+}
+
+export type StalkerChallengeConsumeResult =
+    | {
+          kind: 'consumed';
+          challenge: StalkerChallenge;
+      }
+    | { kind: 'invalid' };
+
+interface StalkerChallengeRecord {
+    senderId: number;
+    attemptRef: string;
+    expiresAt: number;
+    challenge: StalkerChallenge;
+}
+
+export interface StalkerChallengeRegistryOptions {
+    now?: () => number;
+    random?: (size: number) => Buffer;
+}
+
+/**
+ * Owns opaque one-shot continuation capabilities in Electron main.
+ *
+ * No reference or challenge payload is enumerable or serializable. Callers
+ * should return only the generated reference through the typed IPC boundary.
+ */
+export class StalkerChallengeRegistry {
+    readonly #records = new Map<string, StalkerChallengeRecord>();
+    readonly #attempts = new Map<number, Map<string, Set<string>>>();
+    readonly #senderRefs = new Map<number, Set<string>>();
+    readonly #now: () => number;
+    readonly #random: (size: number) => Buffer;
+
+    constructor(options: StalkerChallengeRegistryOptions = {}) {
+        this.#now = options.now ?? Date.now;
+        this.#random = options.random ?? randomBytes;
+    }
+
+    get size(): number {
+        this.#pruneExpired();
+        return this.#records.size;
+    }
+
+    issue(
+        senderId: number,
+        attemptRef: string,
+        challenge: StalkerChallenge
+    ): string {
+        validateOwner(senderId, attemptRef);
+        this.#pruneExpired();
+        if (this.#records.size >= MAX_ACTIVE_CHALLENGES) {
+            throw new Error('stalker-challenge-capacity-exceeded');
+        }
+
+        const challengeRef = this.#createUniqueReference();
+        this.#records.set(challengeRef, {
+            attemptRef,
+            challenge: cloneChallenge(challenge),
+            expiresAt: this.#now() + CHALLENGE_TTL_MS,
+            senderId,
+        });
+        addReference(
+            getOrCreateSet(
+                getOrCreateMap(this.#attempts, senderId),
+                attemptRef
+            ),
+            challengeRef
+        );
+        addReference(
+            getOrCreateSet(this.#senderRefs, senderId),
+            challengeRef
+        );
+        return challengeRef;
+    }
+
+    consume(
+        request: StalkerChallengeConsumeRequest
+    ): StalkerChallengeConsumeResult {
+        const record = this.#records.get(request.challengeRef);
+        if (!record) {
+            return { kind: 'invalid' };
+        }
+        if (record.expiresAt <= this.#now()) {
+            this.#deleteReference(request.challengeRef, record);
+            return { kind: 'invalid' };
+        }
+        if (
+            record.senderId !== request.senderId ||
+            record.attemptRef !== request.attemptRef ||
+            record.challenge.kind !== request.responseKind
+        ) {
+            return { kind: 'invalid' };
+        }
+
+        this.#deleteReference(request.challengeRef, record);
+        return {
+            challenge: cloneChallenge(record.challenge),
+            kind: 'consumed',
+        };
+    }
+
+    invalidateAttempt(senderId: number, attemptRef: string): void {
+        const senderAttempts = this.#attempts.get(senderId);
+        const refs = senderAttempts?.get(attemptRef);
+        if (!refs) {
+            return;
+        }
+
+        for (const ref of [...refs]) {
+            const record = this.#records.get(ref);
+            if (record) {
+                this.#deleteReference(ref, record);
+            }
+        }
+    }
+
+    invalidateSender(senderId: number): void {
+        const refs = this.#senderRefs.get(senderId);
+        if (!refs) {
+            return;
+        }
+
+        for (const ref of [...refs]) {
+            const record = this.#records.get(ref);
+            if (record) {
+                this.#deleteReference(ref, record);
+            }
+        }
+    }
+
+    #createUniqueReference(): string {
+        for (
+            let attempt = 0;
+            attempt < MAX_REFERENCE_GENERATION_ATTEMPTS;
+            attempt += 1
+        ) {
+            const bytes = this.#random(CHALLENGE_RANDOM_BYTES);
+            if (bytes.byteLength !== CHALLENGE_RANDOM_BYTES) {
+                break;
+            }
+            const ref = bytes.toString('base64url');
+            if (!this.#records.has(ref)) {
+                return ref;
+            }
+        }
+        throw new Error('stalker-challenge-reference-generation-failed');
+    }
+
+    #pruneExpired(): void {
+        const now = this.#now();
+        for (const [ref, record] of this.#records) {
+            if (record.expiresAt <= now) {
+                this.#deleteReference(ref, record);
+            }
+        }
+    }
+
+    #deleteReference(ref: string, record: StalkerChallengeRecord): void {
+        this.#records.delete(ref);
+
+        const senderRefs = this.#senderRefs.get(record.senderId);
+        senderRefs?.delete(ref);
+        if (senderRefs?.size === 0) {
+            this.#senderRefs.delete(record.senderId);
+        }
+
+        const senderAttempts = this.#attempts.get(record.senderId);
+        const attemptRefs = senderAttempts?.get(record.attemptRef);
+        attemptRefs?.delete(ref);
+        if (attemptRefs?.size === 0) {
+            senderAttempts?.delete(record.attemptRef);
+        }
+        if (senderAttempts?.size === 0) {
+            this.#attempts.delete(record.senderId);
+        }
+    }
+}
+
+function validateOwner(senderId: number, attemptRef: string): void {
+    if (
+        !Number.isSafeInteger(senderId) ||
+        senderId < 0 ||
+        attemptRef.length === 0 ||
+        attemptRef.length > 256
+    ) {
+        throw new Error('invalid-stalker-challenge-owner');
+    }
+}
+
+function cloneChallenge(challenge: StalkerChallenge): StalkerChallenge {
+    return Object.freeze({ ...challenge });
+}
+
+function getOrCreateMap(
+    map: Map<number, Map<string, Set<string>>>,
+    key: number
+): Map<string, Set<string>> {
+    const existing = map.get(key);
+    if (existing) {
+        return existing;
+    }
+    const created = new Map<string, Set<string>>();
+    map.set(key, created);
+    return created;
+}
+
+function getOrCreateSet<Key>(
+    map: Map<Key, Set<string>>,
+    key: Key
+): Set<string> {
+    const existing = map.get(key);
+    if (existing) {
+        return existing;
+    }
+    const created = new Set<string>();
+    map.set(key, created);
+    return created;
+}
+
+function addReference(refs: Set<string>, ref: string): void {
+    refs.add(ref);
+}