diff --git a/packages/gittensory-engine/src/index.ts b/packages/gittensory-engine/src/index.ts
index d5b02bdef0..61e28496c2 100644
--- a/packages/gittensory-engine/src/index.ts
+++ b/packages/gittensory-engine/src/index.ts
@@ -672,3 +672,8 @@ export {
   SECRET_PATTERNS,
   redactSecrets,
 } from "./subprocess-env.js";
+
+// Shared telemetry-anonymization primitive (#5680) — one source of truth for the per-instance-secret HMAC
+// hashing both Orb's self-host collector and AMS's export path use before repo/PR identifiers leave the
+// instance.
+export { generateAnonSecret, hmacAnonymize } from "./telemetry/anonymize.js";
diff --git a/packages/gittensory-engine/src/telemetry/anonymize.ts b/packages/gittensory-engine/src/telemetry/anonymize.ts
new file mode 100644
index 0000000000..78786186b8
--- /dev/null
+++ b/packages/gittensory-engine/src/telemetry/anonymize.ts
@@ -0,0 +1,29 @@
+// Shared telemetry-anonymization primitive (#5680): one source of truth for the per-instance-secret HMAC
+// hashing every self-hosted product (Orb's `src/selfhost/orb-collector.ts`, and AMS's own export path) uses
+// to anonymize repo/PR identifiers before they leave the instance. Extracted out of Orb-only code so a second,
+// independently-maintained implementation never drifts from this one -- a weaker hash or a reused secret in
+// only one of the two would be a real privacy bug, not style debt.
+//
+// Deliberately narrow: secret PERSISTENCE (where/how it's stored -- D1 for Orb, local SQLite for AMS) stays in
+// each product's own store, since that's genuinely different per product. Only the pure hash/generate math
+// lives here.
+import { createHmac, randomBytes } from "node:crypto";
+
+/**
+ * Generate a fresh, single-purpose 256-bit anonymization secret (64 hex chars). Each product persists this
+ * once per instance in its own store and reuses it on every export, so the same raw value always hashes the
+ * same way. Never derived from, or shared with, any other credential (App private keys, webhook secrets) --
+ * key separation means a leaked anonymization secret can't be used to forge or decrypt anything else.
+ */
+export function generateAnonSecret(): string {
+  return randomBytes(32).toString("hex");
+}
+
+/**
+ * HMAC-SHA256 `value` with the instance's own anonymization secret, truncated to 24 hex chars. The collector
+ * receiving the output never holds `secret`, so it can never reverse the hash back to the original value --
+ * it can only tell that two exports carrying the same hash referred to the same underlying repo/PR.
+ */
+export function hmacAnonymize(value: string, secret: string): string {
+  return createHmac("sha256", secret).update(value).digest("hex").slice(0, 24);
+}
diff --git a/packages/gittensory-engine/test/anonymize.test.ts b/packages/gittensory-engine/test/anonymize.test.ts
new file mode 100644
index 0000000000..0fc3ef7562
--- /dev/null
+++ b/packages/gittensory-engine/test/anonymize.test.ts
@@ -0,0 +1,40 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+
+import { generateAnonSecret, hmacAnonymize } from "../dist/index.js";
+
+test("generateAnonSecret: returns a 64-char hex string (256-bit secret)", () => {
+  const secret = generateAnonSecret();
+  assert.equal(secret.length, 64);
+  assert.match(secret, /^[0-9a-f]{64}$/);
+});
+
+test("generateAnonSecret: two calls never collide", () => {
+  assert.notEqual(generateAnonSecret(), generateAnonSecret());
+});
+
+test("hmacAnonymize: deterministic — same value+secret always hashes the same", () => {
+  const secret = "fixed-secret-for-test";
+  assert.equal(hmacAnonymize("acme/widgets", secret), hmacAnonymize("acme/widgets", secret));
+});
+
+test("hmacAnonymize: different values under the same secret hash differently", () => {
+  const secret = "fixed-secret-for-test";
+  assert.notEqual(hmacAnonymize("acme/widgets", secret), hmacAnonymize("acme/other", secret));
+});
+
+test("hmacAnonymize: the same value under different secrets hashes differently", () => {
+  assert.notEqual(hmacAnonymize("acme/widgets", "secret-a"), hmacAnonymize("acme/widgets", "secret-b"));
+});
+
+test("hmacAnonymize: output is truncated to 24 hex chars", () => {
+  const hash = hmacAnonymize("acme/widgets#42", "fixed-secret-for-test");
+  assert.equal(hash.length, 24);
+  assert.match(hash, /^[0-9a-f]{24}$/);
+});
+
+test("hmacAnonymize: matches Orb's own pre-extraction output for a known vector (regression)", () => {
+  // Fixed vector captured from the original inline `hmacField` in orb-collector.ts before extraction —
+  // guards against the refactor silently changing Orb's live anonymized output.
+  assert.equal(hmacAnonymize("acme/widgets", "known-fixed-secret"), "7323d8850fac6d7c2c4bdfae");
+});
diff --git a/src/selfhost/orb-collector.ts b/src/selfhost/orb-collector.ts
index 7b78885fa4..2ac7320b0f 100644
--- a/src/selfhost/orb-collector.ts
+++ b/src/selfhost/orb-collector.ts
@@ -15,7 +15,8 @@
 // No diffs, no code, no comments, no logins, no commit SHAs — only verdict + outcome + reversal + a bucketed
 // reason category + cycle time, with repo/PR identifiers HMAC'd by a key the collector never holds (so it
 // can never de-anonymize).
-import { createHash, createHmac, randomBytes } from "node:crypto";
+import { createHash, createHmac } from "node:crypto";
+import { generateAnonSecret, hmacAnonymize } from "../../packages/gittensory-engine/src/telemetry/anonymize.js";
 import { incr } from "./metrics";
 
 /** Key under which the per-instance anonymization secret is persisted in system_flags. */
@@ -60,11 +61,6 @@ function instanceId(anonSecret: string): string {
   return createHash("sha256").update(seed).digest("hex").slice(0, 16);
 }
 
-/** HMAC a string with the instance's own secret for anonymized export. */
-function hmacField(value: string, secret: string): string {
-  return createHmac("sha256", secret).update(value).digest("hex").slice(0, 24);
-}
-
 /**
  * The instance's DEDICATED anonymization secret: a 256-bit random key generated once and persisted in
  * system_flags, then reused on every export. Stable across restarts so a repo/PR always hashes the same
@@ -81,7 +77,7 @@ export async function getOrCreateAnonSecret(db: D1Database): Promise<string> {
   };
   const existing = await read();
   if (existing) return existing;
-  const generated = randomBytes(32).toString("hex"); // 256-bit, 64 hex chars
+  const generated = generateAnonSecret(); // 256-bit, 64 hex chars
   // Race-safe across instances sharing a Postgres DB: OR IGNORE keeps the first writer's key; the re-read
   // returns whichever value won, so every instance converges on the same secret.
   await db
@@ -188,8 +184,8 @@ export async function exportOrbBatch(db: D1Database, batchSize = 200, fetchFn: t
   const payload: OrbExportPayload = {
     instance_id: instance,
     events: results.map((r) => ({
-      repo_hash: anonymize ? hmacField(r.project, secret) : r.project,
-      pr_hash: anonymize ? hmacField(r.target_id, secret) : r.target_id,
+      repo_hash: anonymize ? hmacAnonymize(r.project, secret) : r.project,
+      pr_hash: anonymize ? hmacAnonymize(r.target_id, secret) : r.target_id,
       gate_verdict: r.verdict,
       outcome: r.outcome,
       reversal_flag: r.reverted ? "reverted" : r.reopened ? "reopened" : "none",
diff --git a/test/unit/engine-telemetry-anonymize.test.ts b/test/unit/engine-telemetry-anonymize.test.ts
new file mode 100644
index 0000000000..d26e6ad5c5
--- /dev/null
+++ b/test/unit/engine-telemetry-anonymize.test.ts
@@ -0,0 +1,29 @@
+// App-vitest coverage for the engine telemetry-anonymization primitive (#5680). codecov/patch is computed from
+// this app vitest run (vitest.config coverage includes packages/gittensory-engine/src/**), so the changed engine
+// lines need a vitest test that imports the SRC directly, in addition to the engine's own node:test suite.
+import { describe, expect, it } from "vitest";
+import { generateAnonSecret, hmacAnonymize } from "../../packages/gittensory-engine/src/telemetry/anonymize";
+
+describe("engine telemetry-anonymize primitive (#5680)", () => {
+  it("generateAnonSecret returns a 64-char hex string and never collides across calls", () => {
+    const a = generateAnonSecret();
+    const b = generateAnonSecret();
+    expect(a).toMatch(/^[0-9a-f]{64}$/);
+    expect(b).toMatch(/^[0-9a-f]{64}$/);
+    expect(a).not.toBe(b);
+  });
+
+  it("hmacAnonymize is deterministic per value+secret, differs across values and across secrets, truncated to 24 hex chars", () => {
+    const secret = "fixed-secret-for-test";
+    expect(hmacAnonymize("acme/widgets", secret)).toBe(hmacAnonymize("acme/widgets", secret));
+    expect(hmacAnonymize("acme/widgets", secret)).not.toBe(hmacAnonymize("acme/other", secret));
+    expect(hmacAnonymize("acme/widgets", "secret-a")).not.toBe(hmacAnonymize("acme/widgets", "secret-b"));
+    expect(hmacAnonymize("acme/widgets#42", secret)).toMatch(/^[0-9a-f]{24}$/);
+  });
+
+  it("matches Orb's own pre-extraction output for a known vector (regression)", () => {
+    // Fixed vector captured from the original inline `hmacField` in orb-collector.ts before extraction —
+    // guards against the refactor silently changing Orb's live anonymized output.
+    expect(hmacAnonymize("acme/widgets", "known-fixed-secret")).toBe("7323d8850fac6d7c2c4bdfae");
+  });
+});