diff --git a/src/lib/__tests__/caller.test.ts b/src/lib/__tests__/caller.test.ts
index 3c4212a..52e7388 100644
--- a/src/lib/__tests__/caller.test.ts
+++ b/src/lib/__tests__/caller.test.ts
@@ -120,20 +120,73 @@ describe("attribution", () => {
   });
 });
 
-/* ── The guard is on the class, and only on the class ───────────────────── */
+/* ── The guard is on the class, and only on the class ─────────────────── */
+
+/**
+ * Every comparison against a permission set in a file, with the argument it was
+ * handed.
+ *
+ * This is a text scan, so it reads comments as well as code and cannot tell the
+ * difference. Nothing in this file may spell the pattern out in prose — doing so
+ * makes the guard report itself, which is a failure that looks exactly like a
+ * real one and wastes the next reader's afternoon.
+ */
+const COMPARISON = /\.actor\b\s*\.\s*includes\(([^)]*)\)/g;
+
+/**
+ * Whether one such comparison is testing something that is not a class.
+ *
+ * `transition.actor` is a PERMISSION SET — a list of classes. Two things may
+ * legitimately be tested against it, and they are both classes:
+ *
+ *   - a caller's `kind`, which is the runtime check `applyAction` performs;
+ *   - a class named outright, which is how a caller asks a question ABOUT the
+ *     permission set rather than about a caller. `personActionsFor` does this:
+ *     "which actions may a person fire" is precisely what a permission set is
+ *     for, and the answer drives which buttons exist.
+ *
+ * What is forbidden is comparing an IDENTITY against it — a user id, an agent
+ * name, any string naming who rather than which class. That guard answers for
+ * the strings it lists and has to guess for the rest, so an unlisted caller
+ * either gets in or is locked out for having a new name, and a caller that picks
+ * a listed name gets in on the strength of the name alone. F4 exists because
+ * `actor` conflated the two; a check that cannot tell them apart either is the
+ * same defect one level up.
+ *
+ * The permitted literals are read off the registry rather than written here, so
+ * a third class added to `vocabulary.json` is permitted the moment it is
+ * declared, and an agent name — `"checkpoint"`, `"grouping"`, `"migration"` —
+ * is never one of them.
+ *
+ * A class held in a variable is still flagged. That is deliberate: it is rare,
+ * it is indistinguishable from an identity by reading, and the two call sites in
+ * this codebase both have a better form available. Erring tight on a check like
+ * this costs an author one line of justification; erring loose costs the guard.
+ */
+function comparesANonClass(argument: string): boolean {
+  const text = argument.trim();
+  if (/\.kind\b/.test(text)) return false;
+  return !REGISTRY_CLASSES.some((className) => text === `"${className}"` || text === `'${className}'`);
+}
 
 describe("no identity string is ever compared against a permission list", () => {
+  it("knows an identity from a class", () => {
+    // The guard was narrowed in R2, so what it still catches is asserted rather
+    // than assumed. A check that was loosened without this is a check nobody can
+    // tell from a deleted one.
+    expect(comparesANonClass("options.by.kind")).toBe(false);
+    expect(comparesANonClass("by.kind")).toBe(false);
+    for (const className of REGISTRY_CLASSES) {
+      expect(comparesANonClass(`"${className}"`), `${className} is a class the registry declares`).toBe(false);
+    }
+    // Identities, every one of which the old field could hold and none of which
+    // is a class.
+    for (const identity of ['"checkpoint"', '"grouping"', '"migration"', '"rae@webflow.com"', "rec.owner", "userId", "entry.by.userId"]) {
+      expect(comparesANonClass(identity), `${identity} is an identity, not a class`).toBe(true);
+    }
+  });
+
   it("is true of every file under src/", () => {
-    /**
-     * The shape this chunk exists to prevent: a guard that asks whether an
-     * identity string is in a list of permitted names. It answers for the
-     * strings it lists and has to guess for the rest, so an unlisted caller
-     * either gets in or is locked out for having a new name — and a caller that
-     * picks a listed name gets in on the strength of the name alone.
-     *
-     * `transition.actor` may only ever be tested against a caller's `kind`.
-     * This reads every source file and checks that.
-     */
     const files: string[] = [];
     const walk = (dir: string) => {
       for (const entry of readdirSync(dir, { withFileTypes: true })) {
@@ -147,8 +200,8 @@ describe("no identity string is ever compared against a permission list", () =>
     const offenders: string[] = [];
     for (const file of files) {
       const source = readFileSync(file, "utf8");
-      for (const match of source.matchAll(/\.actor\b\s*\.\s*includes\(([^)]*)\)/g)) {
-        if (!/\.kind\b/.test(match[1])) offenders.push(`${path.relative(srcDir, file)}: ${match[0]}`);
+      for (const match of source.matchAll(COMPARISON)) {
+        if (comparesANonClass(match[1])) offenders.push(`${path.relative(srcDir, file)}: ${match[0]}`);
       }
     }
     expect(offenders).toEqual([]);
diff --git a/src/lib/__tests__/digest-arrival.test.ts b/src/lib/__tests__/digest-arrival.test.ts
index c30c526..742bcca 100644
--- a/src/lib/__tests__/digest-arrival.test.ts
+++ b/src/lib/__tests__/digest-arrival.test.ts
@@ -21,6 +21,7 @@ import {
   type IssueCase,
   type IssueState,
 } from "../issue-case";
+import type { Caller } from "../caller";
 import { recordCheckpointReading } from "../checkpoint-evaluation";
 import { normalizePerformanceThresholds } from "../performanceThresholds";
 import { ISSUE_TRANSITIONS, QUEUES, WORK_STATES, type IssueAction } from "../vocabulary";
@@ -43,6 +44,15 @@ const AT = "2026-08-25T06:00:00.000Z";
 const DATE = "2026-08-25";
 const APP = "https://watch.example.com/page-watch";
 
+/**
+ * Whoever walked the case down the lifecycle below.
+ *
+ * The address is the case's id and nothing else, so who moved it is exactly the
+ * kind of fact the link is not allowed to carry. This exists to satisfy the
+ * transition guard and is never asserted on.
+ */
+const PERSON: Caller = { kind: "person", userId: "rae@webflow.com" };
+
 function caseOf(overrides: Partial<IssueCase> = {}): IssueCase {
   return {
     id: "PW-2291",
@@ -129,9 +139,9 @@ describe("the case route", () => {
      */
     const link = digestOf([caseOf()]).sections[0].lines[0].href;
     let issue = caseOf();
-    issue = accept(issue, { actor: "person", at: AT });
-    issue = start(issue, { actor: "person", at: AT });
-    issue = markFixed(issue, { actor: "person", at: AT });
+    issue = accept(issue, { by: PERSON, at: AT });
+    issue = start(issue, { by: PERSON, at: AT });
+    issue = markFixed(issue, { by: PERSON, at: AT });
     issue = recordCheckpointReading(issue, { interval: "7d", outcome: "disagreed", at: AT }).issue;
     expect(issue.state).toBe("reopened");
     expect(issue.id).toBe("PW-2291");
@@ -187,7 +197,7 @@ describe("the context banner", () => {
 
   it("repeats the line the message wrote, because both come from one writer", () => {
     const reopened = recordCheckpointReading(
-      markFixed(caseOf({ state: "in_progress" }), { actor: "person", at: AT }),
+      markFixed(caseOf({ state: "in_progress" }), { by: PERSON, at: AT }),
       { interval: "7d", outcome: "disagreed", at: AT },
     ).issue;
     const digest = digestOf([reopened]);
diff --git a/src/lib/__tests__/digest.test.ts b/src/lib/__tests__/digest.test.ts
index 2326138..d1b08f5 100644
--- a/src/lib/__tests__/digest.test.ts
+++ b/src/lib/__tests__/digest.test.ts
@@ -14,6 +14,7 @@ import { digestLinks, renderDigestMessage } from "../digest-email";
 import { DIGEST_CADENCE_LABEL } from "../digestCadence";
 import { formatImpact } from "../impact-format";
 import { markFixed, scheduleCheckpoints, type IssueCase } from "../issue-case";
+import type { Caller } from "../caller";
 import { recordCheckpointReading } from "../checkpoint-evaluation";
 import { normalizePerformanceThresholds } from "../performanceThresholds";
 import { casePath } from "../paths";
@@ -61,15 +62,21 @@ function caseOf(overrides: Partial<IssueCase> = {}): IssueCase {
   };
 }
 
+/**
+ * Whoever marked the fix. The digest never renders them — it is about cases, not
+ * about who moved them — so this exists only to satisfy the transition guard.
+ */
+const PERSON: Caller = { kind: "person", userId: "rae@webflow.com" };
+
 /** A case the system brought back, produced by the evaluator rather than posed. */
 function cameBackCase(overrides: Partial<IssueCase> = {}): IssueCase {
-  const fixed = markFixed(caseOf({ state: "in_progress", ...overrides }), { actor: "person", at: AT });
+  const fixed = markFixed(caseOf({ state: "in_progress", ...overrides }), { by: PERSON, at: AT });
   return recordCheckpointReading(fixed, { interval: "7d", outcome: "disagreed", at: AT }).issue;
 }
 
 /** A fixed case still waiting: three checkpoints scheduled, nothing read. */
 function heldCase(overrides: Partial<IssueCase> = {}): IssueCase {
-  return markFixed(caseOf({ state: "in_progress", ...overrides }), { actor: "person", at: AT });
+  return markFixed(caseOf({ state: "in_progress", ...overrides }), { by: PERSON, at: AT });
 }
 
 /** A fixed case whose three checks all failed to read — evaluation rule 4. */
@@ -81,7 +88,7 @@ function unreadableCase(overrides: Partial<IssueCase> = {}): IssueCase {
       attempts: 2,
       result: "unavailable" as const,
     })),
-    history: [{ at: AT, from: "in_progress", to: "fixed", actor: "person" }],
+    history: [{ at: AT, from: "in_progress", to: "fixed", by: PERSON }],
     ...overrides,
   });
 }
diff --git a/src/lib/__tests__/webhook.test.ts b/src/lib/__tests__/webhook.test.ts
index a3e3887..5a04545 100644
--- a/src/lib/__tests__/webhook.test.ts
+++ b/src/lib/__tests__/webhook.test.ts
@@ -7,6 +7,7 @@ import {
 import { buildDigest, type Digest } from "../digest";
 import { renderDigestMessage } from "../digest-email";
 import { markFixed, type IssueCase } from "../issue-case";
+import type { Caller } from "../caller";
 import { recordCheckpointReading } from "../checkpoint-evaluation";
 import { normalizePerformanceThresholds } from "../performanceThresholds";
 import { pendingPage } from "../mutations";
@@ -18,6 +19,12 @@ afterEach(() => {
 
 const AT = "2026-08-04T06:00:00.000Z";
 
+/**
+ * Whoever marked the fix. The payload is the digest message and the digest is
+ * about cases, so this only ever satisfies the transition guard.
+ */
+const PERSON: Caller = { kind: "person", userId: "rae@webflow.com" };
+
 function caseOf(overrides: Partial<IssueCase> = {}): IssueCase {
   return {
     id: "PW-1",
@@ -71,7 +78,7 @@ describe("alert webhook", () => {
      * sections, same sentences.
      */
     const digest = digestOf([
-      recordCheckpointReading(markFixed(caseOf(), { actor: "person", at: AT }), {
+      recordCheckpointReading(markFixed(caseOf(), { by: PERSON, at: AT }), {
         interval: "7d",
         outcome: "disagreed",
         at: AT,