From c2bb52dd08086a0fce9989bf1d5f7a2f1a80a559 Mon Sep 17 00:00:00 2001
From: "sentry-junior[bot]"
 <264270552+sentry-junior[bot]@users.noreply.github.com>
Date: Wed, 16 Sep 2026 02:46:07 +0000
Subject: [PATCH 1/3] refactor(junior): add core feature registration

Co-Authored-By: David Cramer <david@sentry.io>
---
 packages/junior/src/app.ts                    |  2 +
 .../junior/src/chat/briefs/registration.ts    |  8 ----
 .../junior/src/chat/core-features/README.md   |  7 ++++
 .../src/chat/core-features/registration.ts    | 40 +++++++++++++++++++
 .../junior/src/chat/plugins/agent-hooks.ts    | 18 +++++----
 .../src/chat/plugins/conversation-events.ts   |  8 ++--
 .../junior/src/chat/plugins/task-runner.ts    | 12 +++---
 .../junior/src/chat/plugins/user-pages.ts     |  5 ++-
 packages/junior/src/cli/plugins.ts            | 12 +++++-
 packages/junior/tests/unit/app-config.test.ts | 19 +++++++++
 10 files changed, 101 insertions(+), 30 deletions(-)
 create mode 100644 packages/junior/src/chat/core-features/README.md
 create mode 100644 packages/junior/src/chat/core-features/registration.ts

diff --git a/packages/junior/src/app.ts b/packages/junior/src/app.ts
index 10c6546c88..aa731d449c 100644
--- a/packages/junior/src/app.ts
+++ b/packages/junior/src/app.ts
@@ -28,6 +28,7 @@ import {
   type ExperimentalFeaturesConfig,
 } from "@/chat/experimental";
 import { setBriefsConfig } from "@/chat/briefs/registration";
+import { assertNoCoreFeatureNameCollisions } from "@/chat/core-features/registration";
 import {
   getSandboxResourceConfig,
   setSandboxResourceConfig,
@@ -693,6 +694,7 @@ export async function createApp(options?: JuniorAppOptions): Promise<Hono> {
     validateBuildIncludesPluginPackages(pluginConfig, virtualConfig);
   }
   validateBuildIncludesPluginRuntimeRegistrations(plugins, virtualConfig);
+  assertNoCoreFeatureNameCollisions(configuredPlugins?.registrations ?? []);
   validatePlugins(plugins);
   getDb();
   const shouldValidatePluginCatalog =
diff --git a/packages/junior/src/chat/briefs/registration.ts b/packages/junior/src/chat/briefs/registration.ts
index c1320dd3dd..e771766574 100644
--- a/packages/junior/src/chat/briefs/registration.ts
+++ b/packages/junior/src/chat/briefs/registration.ts
@@ -1,6 +1,3 @@
-import type { PluginRegistration } from "@sentry/junior-plugin-api";
-import { briefsTaskRegistration } from "./task";
-
 type BriefsConfig = Readonly<{ enabled?: boolean }>;
 
 let configuredBriefs: BriefsConfig = {};
@@ -16,8 +13,3 @@ export function setBriefsConfig(config?: { enabled?: boolean }): BriefsConfig {
 export function isBriefsEnabled(): boolean {
   return configuredBriefs.enabled === true;
 }
-
-/** Return enabled core task registrations. */
-export function coreTaskRegistrations(): PluginRegistration[] {
-  return isBriefsEnabled() ? [briefsTaskRegistration] : [];
-}
diff --git a/packages/junior/src/chat/core-features/README.md b/packages/junior/src/chat/core-features/README.md
new file mode 100644
index 0000000000..2fa5e769bd
--- /dev/null
+++ b/packages/junior/src/chat/core-features/README.md
@@ -0,0 +1,7 @@
+# Core features
+
+Core features use the plugin runtime contract for shared execution context. They do not use plugin package discovery or the installed plugin catalog.
+
+`registration.ts` is the source of truth for core feature names and enabled registrations. Runtime consumers must join core features with installed plugins through `runtimeFeatureRegistrations()`. Stored Conversation events also include disabled core features so old events remain readable.
+
+An installed plugin must not use a core feature name.
diff --git a/packages/junior/src/chat/core-features/registration.ts b/packages/junior/src/chat/core-features/registration.ts
new file mode 100644
index 0000000000..cf04251a33
--- /dev/null
+++ b/packages/junior/src/chat/core-features/registration.ts
@@ -0,0 +1,40 @@
+import type { PluginRegistration } from "@sentry/junior-plugin-api";
+import { isBriefsEnabled } from "@/chat/briefs/registration";
+import { briefsTaskRegistration } from "@/chat/briefs/task";
+
+const coreFeatures = [
+  { isEnabled: isBriefsEnabled, registration: briefsTaskRegistration },
+];
+const CORE_FEATURE_NAMES = new Set(
+  coreFeatures.map((feature) => feature.registration.manifest.name),
+);
+
+/** Return enabled core feature registrations. */
+export function coreFeatureRegistrations(): PluginRegistration[] {
+  return coreFeatures
+    .filter((feature) => feature.isEnabled())
+    .map((feature) => feature.registration);
+}
+
+/** Return core features followed by installed plugins. */
+export function runtimeFeatureRegistrations(
+  plugins: PluginRegistration[],
+  options: { includeDisabled?: boolean } = {},
+): PluginRegistration[] {
+  const coreRegistrations = options.includeDisabled
+    ? coreFeatures.map((feature) => feature.registration)
+    : coreFeatureRegistrations();
+  return [...coreRegistrations, ...plugins];
+}
+
+/** Reject a plugin that claims a core feature name. */
+export function assertNoCoreFeatureNameCollisions(
+  plugins: PluginRegistration[],
+): void {
+  for (const plugin of plugins) {
+    const name = plugin.manifest.name;
+    if (CORE_FEATURE_NAMES.has(name)) {
+      throw new Error(`Plugin registration name "${name}" is reserved by core`);
+    }
+  }
+}
diff --git a/packages/junior/src/chat/plugins/agent-hooks.ts b/packages/junior/src/chat/plugins/agent-hooks.ts
index 9069fb01d3..36198790f4 100644
--- a/packages/junior/src/chat/plugins/agent-hooks.ts
+++ b/packages/junior/src/chat/plugins/agent-hooks.ts
@@ -57,7 +57,10 @@ import { z } from "zod";
 import { workspaceRepoCheckoutPath } from "@/chat/workspaces/checkout-path";
 import { listWorkspaceNamesByRepository } from "@/chat/workspaces/store";
 import { createCodeChangePublisher } from "@/chat/code/publisher";
-import { coreTaskRegistrations } from "@/chat/briefs/registration";
+import {
+  assertNoCoreFeatureNameCollisions,
+  runtimeFeatureRegistrations,
+} from "@/chat/core-features/registration";
 
 /** Signal that a plugin intentionally denied a tool execution. */
 export class PluginHookDeniedError extends Error {
@@ -382,6 +385,7 @@ function logInvalidPromptContributions(args: {
 
 /** Validate plugin identity before it can affect process-wide hooks. */
 export function validatePlugins(plugins: PluginRegistration[]): void {
+  assertNoCoreFeatureNameCollisions(plugins);
   const seen = new Set<string>();
   for (const plugin of plugins) {
     const name = plugin.manifest.name;
@@ -462,7 +466,7 @@ export async function getPluginSystemPromptContributions(
 ): Promise<PluginPromptContributionContext[]> {
   const contributions: PluginPromptContributionContext[] = [];
   let totalChars = 0;
-  for (const plugin of getPlugins()) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.systemPrompt;
     if (!hook) {
@@ -532,7 +536,7 @@ export async function getPluginUserPromptContributions(args: {
   const contributions: PluginPromptContributionContext[] = [];
   let totalChars = 0;
   let totalContextBytes = 0;
-  for (const plugin of getPlugins()) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.userPrompt;
     if (!hook) {
@@ -612,7 +616,7 @@ export function getPluginTools(
   sandbox: PluginSandbox = createSandboxCapability(context.workspace),
 ): Record<string, AnyToolDefinition> {
   const tools: Record<string, AnyToolDefinition> = {};
-  for (const plugin of getPlugins()) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.tools;
     if (!hook) {
@@ -872,7 +876,7 @@ export function getPluginRoutes(options: {
   const seen = new Set<string>();
   const methodsByPath = new Map<string, Set<PluginRouteMethod>>();
 
-  for (const plugin of getPlugins()) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.routes;
     if (!hook) {
@@ -991,7 +995,7 @@ export function getPluginRoutes(options: {
 export function getPluginApiRoutes(): PluginApiRouteRegistration[] {
   const routes: PluginApiRouteRegistration[] = [];
 
-  for (const plugin of getPlugins()) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.apiRoutes;
     if (!hook) {
@@ -1356,7 +1360,7 @@ export async function getPluginOperationalReports(
   nowMs: number,
 ): Promise<PluginOperationalReport[]> {
   const reports: PluginOperationalReport[] = [];
-  for (const plugin of [...coreTaskRegistrations(), ...getPlugins()]) {
+  for (const plugin of runtimeFeatureRegistrations(getPlugins())) {
     const pluginName = plugin.manifest.name;
     const hook = plugin.hooks?.operationalReport;
     if (!hook) {
diff --git a/packages/junior/src/chat/plugins/conversation-events.ts b/packages/junior/src/chat/plugins/conversation-events.ts
index e5fa2388d7..4ac655ca70 100644
--- a/packages/junior/src/chat/plugins/conversation-events.ts
+++ b/packages/junior/src/chat/plugins/conversation-events.ts
@@ -5,7 +5,7 @@ import type {
   PluginConversationEventValue,
   PluginRegistration,
 } from "@sentry/junior-plugin-api";
-import { briefsTaskRegistration } from "@/chat/briefs/task";
+import { runtimeFeatureRegistrations } from "@/chat/core-features/registration";
 import { getConversationEventStore } from "@/chat/db";
 import { getPlugins } from "./agent-hooks";
 
@@ -80,9 +80,9 @@ export function renderPluginConversationEvent(args: {
   namespace: string;
   version: number;
 }): ConversationEventPresentation | undefined {
-  const plugin = [briefsTaskRegistration, ...getPlugins()].find(
-    (candidate) => candidate.manifest.name === args.namespace,
-  );
+  const plugin = runtimeFeatureRegistrations(getPlugins(), {
+    includeDisabled: true,
+  }).find((candidate) => candidate.manifest.name === args.namespace);
   const definition = plugin?.conversationEvents?.find(
     (candidate) =>
       candidate.eventName === args.name && candidate.version === args.version,
diff --git a/packages/junior/src/chat/plugins/task-runner.ts b/packages/junior/src/chat/plugins/task-runner.ts
index a4f7262590..5ae13eaea4 100644
--- a/packages/junior/src/chat/plugins/task-runner.ts
+++ b/packages/junior/src/chat/plugins/task-runner.ts
@@ -47,7 +47,7 @@ import {
   getTurnRecord,
   type TurnRecord,
 } from "@/chat/task-execution/checkpoint";
-import { coreTaskRegistrations } from "@/chat/briefs/registration";
+import { runtimeFeatureRegistrations } from "@/chat/core-features/registration";
 import { getPlugins } from "./agent-hooks";
 import {
   pluginTaskId,
@@ -442,7 +442,7 @@ function taskPluginContext(
 }
 
 function findPluginTask(message: PluginTaskQueueMessage) {
-  const plugin = [...coreTaskRegistrations(), ...getPlugins()].find(
+  const plugin = runtimeFeatureRegistrations(getPlugins()).find(
     (candidate) => candidate.manifest.name === message.plugin,
   );
   if (!plugin?.tasks || !Object.hasOwn(plugin.tasks, message.name)) {
@@ -458,11 +458,9 @@ export async function scheduleSessionCompletedPluginTasks(
   options: ScheduleSessionCompletedPluginTasksOptions = {},
 ): Promise<void> {
   const coreParams = pluginTaskParamsSchema.parse(params);
-  const taskRegistrations = [
-    ...getPlugins(),
-    ...coreTaskRegistrations(),
-  ].flatMap((plugin) =>
-    Object.keys(plugin.tasks ?? {}).map((name) => ({ name, plugin })),
+  const taskRegistrations = runtimeFeatureRegistrations(getPlugins()).flatMap(
+    (plugin) =>
+      Object.keys(plugin.tasks ?? {}).map((name) => ({ name, plugin })),
   );
   if (taskRegistrations.length === 0) {
     return;
diff --git a/packages/junior/src/chat/plugins/user-pages.ts b/packages/junior/src/chat/plugins/user-pages.ts
index 2573fc4324..eb32ba988e 100644
--- a/packages/junior/src/chat/plugins/user-pages.ts
+++ b/packages/junior/src/chat/plugins/user-pages.ts
@@ -15,11 +15,12 @@ import { getDb } from "@/chat/db";
 import { createPluginLogger } from "@/chat/plugins/logging";
 import { resolveViewerUser } from "@/chat/plugins/viewer";
 import { getPlugins } from "@/chat/plugins/agent-hooks";
+import { runtimeFeatureRegistrations } from "@/chat/core-features/registration";
 
 /** List safe navigation metadata for registered plugin user pages. */
 export function readPluginUserPageLinks(): PluginUserPageLink[] {
   return pluginUserPageLinksSchema.parse(
-    getPlugins().flatMap((plugin) =>
+    runtimeFeatureRegistrations(getPlugins()).flatMap((plugin) =>
       (plugin.userPages ?? []).map((page) => ({
         description: page.description,
         id: page.id,
@@ -50,7 +51,7 @@ export async function readPluginUserPage(input: {
   pluginName: string;
   query: PluginUserPageInput;
 }): Promise<PluginUserPageContent | undefined> {
-  const plugin = getPlugins().find(
+  const plugin = runtimeFeatureRegistrations(getPlugins()).find(
     (candidate) => candidate.manifest.name === input.pluginName,
   );
   const page = plugin?.userPages?.find(
diff --git a/packages/junior/src/cli/plugins.ts b/packages/junior/src/cli/plugins.ts
index 206dbd6360..bb5cef8786 100644
--- a/packages/junior/src/cli/plugins.ts
+++ b/packages/junior/src/cli/plugins.ts
@@ -21,6 +21,10 @@ import {
   validatePluginRegistrations,
 } from "@/chat/plugins/validation";
 import { loadAppPluginSet } from "@/plugin-module";
+import {
+  assertNoCoreFeatureNameCollisions,
+  runtimeFeatureRegistrations,
+} from "@/chat/core-features/registration";
 import {
   pluginCliRegistrationsFromPluginSet,
   pluginCatalogConfigFromPluginSet,
@@ -226,11 +230,15 @@ async function loadPluginRegistrations(args: {
   runtimePlugins: PluginRegistration[];
 }> {
   const pluginSet = args.pluginSet;
+  const cliPlugins = runtimeFeatureRegistrations(
+    pluginCliRegistrationsFromPluginSet(pluginSet),
+  ).filter((registration) => registration.cli);
   if (!pluginSet) {
-    return { cliPlugins: [], runtimePlugins: [] };
+    args.validateConfiguredCommands?.(cliPlugins);
+    return { cliPlugins, runtimePlugins: [] };
   }
 
-  const cliPlugins = pluginCliRegistrationsFromPluginSet(pluginSet);
+  assertNoCoreFeatureNameCollisions(pluginSet.registrations);
   const runtimePlugins = pluginRuntimeRegistrationsFromPluginSet(pluginSet);
   const pluginConfig = pluginCatalogConfigFromPluginSet(pluginSet);
   validatePlugins(runtimePlugins);
diff --git a/packages/junior/tests/unit/app-config.test.ts b/packages/junior/tests/unit/app-config.test.ts
index 2b2c3a3442..687d6b659e 100644
--- a/packages/junior/tests/unit/app-config.test.ts
+++ b/packages/junior/tests/unit/app-config.test.ts
@@ -713,6 +713,25 @@ describe("createApp plugin config", () => {
     expect(pluginCatalogRuntime.getProviders()).toEqual([]);
   });
 
+  it("rejects plugin names reserved by core features", async () => {
+    await expect(
+      createApp({
+        plugins: defineJuniorPlugins([
+          defineJuniorPlugin({
+            manifest: {
+              name: "briefs",
+              displayName: "Briefs",
+              description: "Conflicting Briefs plugin",
+            },
+          }),
+        ]),
+      }),
+    ).rejects.toThrow('Plugin registration name "briefs" is reserved by core');
+
+    expect(getPlugins().map((plugin) => plugin.manifest.name)).toEqual([]);
+    expect(pluginCatalogRuntime.getProviders()).toEqual([]);
+  });
+
   it("rejects invalid plugin names before mutating app config", async () => {
     await createApp({
       plugins: defineJuniorPlugins([]),

From a54032387cf99ca1ed202d4706ce0c772a5b0c4c Mon Sep 17 00:00:00 2001
From: "sentry-junior[bot]"
 <264270552+sentry-junior[bot]@users.noreply.github.com>
Date: Wed, 16 Sep 2026 02:52:01 +0000
Subject: [PATCH 2/3] test(junior): keep app config test within limit

---
 packages/junior/tests/unit/app-config.test.ts | 24 ++++++++-----------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/packages/junior/tests/unit/app-config.test.ts b/packages/junior/tests/unit/app-config.test.ts
index 687d6b659e..b2f3f643b6 100644
--- a/packages/junior/tests/unit/app-config.test.ts
+++ b/packages/junior/tests/unit/app-config.test.ts
@@ -714,22 +714,18 @@ describe("createApp plugin config", () => {
   });
 
   it("rejects plugin names reserved by core features", async () => {
+    const briefsPlugin = defineJuniorPlugin({
+      manifest: {
+        name: "briefs",
+        displayName: "Briefs",
+        description: "Conflicting Briefs plugin",
+      },
+    });
+
     await expect(
-      createApp({
-        plugins: defineJuniorPlugins([
-          defineJuniorPlugin({
-            manifest: {
-              name: "briefs",
-              displayName: "Briefs",
-              description: "Conflicting Briefs plugin",
-            },
-          }),
-        ]),
-      }),
+      createApp({ plugins: defineJuniorPlugins([briefsPlugin]) }),
     ).rejects.toThrow('Plugin registration name "briefs" is reserved by core');
-
-    expect(getPlugins().map((plugin) => plugin.manifest.name)).toEqual([]);
-    expect(pluginCatalogRuntime.getProviders()).toEqual([]);
+    expect(getPlugins()).toEqual([]);
   });
 
   it("rejects invalid plugin names before mutating app config", async () => {

From aefeb5631585fc1a3e83c9098d38efb7d93e91f7 Mon Sep 17 00:00:00 2001
From: "sentry-junior[bot]"
 <264270552+sentry-junior[bot]@users.noreply.github.com>
Date: Wed, 16 Sep 2026 03:00:14 +0000
Subject: [PATCH 3/3] refactor(junior): simplify core feature registration

Co-Authored-By: David Cramer <david@sentry.io>
---
 packages/junior/src/app.ts                    |  4 +-
 packages/junior/src/chat/briefs/task.ts       |  4 +-
 .../junior/src/chat/core-features/README.md   |  6 +--
 .../src/chat/core-features/registration.ts    | 24 +++++------
 .../src/chat/plugins/conversation-events.ts   |  8 ++--
 packages/junior/src/cli/plugins.ts            |  8 +---
 packages/junior/tests/unit/app-config.test.ts | 15 -------
 .../unit/core-feature-registration.test.ts    | 41 +++++++++++++++++++
 8 files changed, 64 insertions(+), 46 deletions(-)
 create mode 100644 packages/junior/tests/unit/core-feature-registration.test.ts

diff --git a/packages/junior/src/app.ts b/packages/junior/src/app.ts
index aa731d449c..f25771a50b 100644
--- a/packages/junior/src/app.ts
+++ b/packages/junior/src/app.ts
@@ -28,7 +28,6 @@ import {
   type ExperimentalFeaturesConfig,
 } from "@/chat/experimental";
 import { setBriefsConfig } from "@/chat/briefs/registration";
-import { assertNoCoreFeatureNameCollisions } from "@/chat/core-features/registration";
 import {
   getSandboxResourceConfig,
   setSandboxResourceConfig,
@@ -694,8 +693,7 @@ export async function createApp(options?: JuniorAppOptions): Promise<Hono> {
     validateBuildIncludesPluginPackages(pluginConfig, virtualConfig);
   }
   validateBuildIncludesPluginRuntimeRegistrations(plugins, virtualConfig);
-  assertNoCoreFeatureNameCollisions(configuredPlugins?.registrations ?? []);
-  validatePlugins(plugins);
+  validatePlugins(configuredPlugins?.registrations ?? []);
   getDb();
   const shouldValidatePluginCatalog =
     hasConfiguredPluginCatalog(pluginConfig) ||
diff --git a/packages/junior/src/chat/briefs/task.ts b/packages/junior/src/chat/briefs/task.ts
index 6e4f30128b..0b84263a18 100644
--- a/packages/junior/src/chat/briefs/task.ts
+++ b/packages/junior/src/chat/briefs/task.ts
@@ -189,8 +189,8 @@ export async function updateConversationBrief(
   );
 }
 
-/** Core task registration kept outside the installed plugin catalog. */
-export const briefsTaskRegistration: PluginRegistration = {
+/** Register Briefs outside the installed plugin catalog. */
+export const briefsFeatureRegistration: PluginRegistration = {
   manifest: {
     name: "briefs",
     displayName: "Briefs",
diff --git a/packages/junior/src/chat/core-features/README.md b/packages/junior/src/chat/core-features/README.md
index 2fa5e769bd..788a4828cf 100644
--- a/packages/junior/src/chat/core-features/README.md
+++ b/packages/junior/src/chat/core-features/README.md
@@ -1,7 +1,5 @@
 # Core features
 
-Core features use the plugin runtime contract for shared execution context. They do not use plugin package discovery or the installed plugin catalog.
+Core features use the plugin runtime contract. They do not use plugin discovery or appear in the installed plugin catalog.
 
-`registration.ts` is the source of truth for core feature names and enabled registrations. Runtime consumers must join core features with installed plugins through `runtimeFeatureRegistrations()`. Stored Conversation events also include disabled core features so old events remain readable.
-
-An installed plugin must not use a core feature name.
+`registration.ts` owns core feature registration and reserved names.
diff --git a/packages/junior/src/chat/core-features/registration.ts b/packages/junior/src/chat/core-features/registration.ts
index cf04251a33..6e8ea900b1 100644
--- a/packages/junior/src/chat/core-features/registration.ts
+++ b/packages/junior/src/chat/core-features/registration.ts
@@ -1,13 +1,14 @@
 import type { PluginRegistration } from "@sentry/junior-plugin-api";
 import { isBriefsEnabled } from "@/chat/briefs/registration";
-import { briefsTaskRegistration } from "@/chat/briefs/task";
+import { briefsFeatureRegistration } from "@/chat/briefs/task";
 
 const coreFeatures = [
-  { isEnabled: isBriefsEnabled, registration: briefsTaskRegistration },
+  { isEnabled: isBriefsEnabled, registration: briefsFeatureRegistration },
 ];
-const CORE_FEATURE_NAMES = new Set(
-  coreFeatures.map((feature) => feature.registration.manifest.name),
-);
+/** Return all core registrations, including disabled features. */
+export function allCoreFeatureRegistrations(): PluginRegistration[] {
+  return coreFeatures.map((feature) => feature.registration);
+}
 
 /** Return enabled core feature registrations. */
 export function coreFeatureRegistrations(): PluginRegistration[] {
@@ -16,24 +17,23 @@ export function coreFeatureRegistrations(): PluginRegistration[] {
     .map((feature) => feature.registration);
 }
 
-/** Return core features followed by installed plugins. */
+/** Return enabled core features followed by installed plugins. */
 export function runtimeFeatureRegistrations(
   plugins: PluginRegistration[],
-  options: { includeDisabled?: boolean } = {},
 ): PluginRegistration[] {
-  const coreRegistrations = options.includeDisabled
-    ? coreFeatures.map((feature) => feature.registration)
-    : coreFeatureRegistrations();
-  return [...coreRegistrations, ...plugins];
+  return [...coreFeatureRegistrations(), ...plugins];
 }
 
 /** Reject a plugin that claims a core feature name. */
 export function assertNoCoreFeatureNameCollisions(
   plugins: PluginRegistration[],
 ): void {
+  const coreNames = new Set(
+    allCoreFeatureRegistrations().map((feature) => feature.manifest.name),
+  );
   for (const plugin of plugins) {
     const name = plugin.manifest.name;
-    if (CORE_FEATURE_NAMES.has(name)) {
+    if (coreNames.has(name)) {
       throw new Error(`Plugin registration name "${name}" is reserved by core`);
     }
   }
diff --git a/packages/junior/src/chat/plugins/conversation-events.ts b/packages/junior/src/chat/plugins/conversation-events.ts
index 4ac655ca70..585e88a89e 100644
--- a/packages/junior/src/chat/plugins/conversation-events.ts
+++ b/packages/junior/src/chat/plugins/conversation-events.ts
@@ -5,7 +5,7 @@ import type {
   PluginConversationEventValue,
   PluginRegistration,
 } from "@sentry/junior-plugin-api";
-import { runtimeFeatureRegistrations } from "@/chat/core-features/registration";
+import { allCoreFeatureRegistrations } from "@/chat/core-features/registration";
 import { getConversationEventStore } from "@/chat/db";
 import { getPlugins } from "./agent-hooks";
 
@@ -80,9 +80,9 @@ export function renderPluginConversationEvent(args: {
   namespace: string;
   version: number;
 }): ConversationEventPresentation | undefined {
-  const plugin = runtimeFeatureRegistrations(getPlugins(), {
-    includeDisabled: true,
-  }).find((candidate) => candidate.manifest.name === args.namespace);
+  const plugin = [...allCoreFeatureRegistrations(), ...getPlugins()].find(
+    (candidate) => candidate.manifest.name === args.namespace,
+  );
   const definition = plugin?.conversationEvents?.find(
     (candidate) =>
       candidate.eventName === args.name && candidate.version === args.version,
diff --git a/packages/junior/src/cli/plugins.ts b/packages/junior/src/cli/plugins.ts
index bb5cef8786..39726e5bb4 100644
--- a/packages/junior/src/cli/plugins.ts
+++ b/packages/junior/src/cli/plugins.ts
@@ -21,10 +21,7 @@ import {
   validatePluginRegistrations,
 } from "@/chat/plugins/validation";
 import { loadAppPluginSet } from "@/plugin-module";
-import {
-  assertNoCoreFeatureNameCollisions,
-  runtimeFeatureRegistrations,
-} from "@/chat/core-features/registration";
+import { runtimeFeatureRegistrations } from "@/chat/core-features/registration";
 import {
   pluginCliRegistrationsFromPluginSet,
   pluginCatalogConfigFromPluginSet,
@@ -238,10 +235,9 @@ async function loadPluginRegistrations(args: {
     return { cliPlugins, runtimePlugins: [] };
   }
 
-  assertNoCoreFeatureNameCollisions(pluginSet.registrations);
   const runtimePlugins = pluginRuntimeRegistrationsFromPluginSet(pluginSet);
   const pluginConfig = pluginCatalogConfigFromPluginSet(pluginSet);
-  validatePlugins(runtimePlugins);
+  validatePlugins(pluginSet.registrations);
   const previousPluginCatalogConfig =
     pluginCatalogRuntime.setConfig(pluginConfig);
   try {
diff --git a/packages/junior/tests/unit/app-config.test.ts b/packages/junior/tests/unit/app-config.test.ts
index b2f3f643b6..2b2c3a3442 100644
--- a/packages/junior/tests/unit/app-config.test.ts
+++ b/packages/junior/tests/unit/app-config.test.ts
@@ -713,21 +713,6 @@ describe("createApp plugin config", () => {
     expect(pluginCatalogRuntime.getProviders()).toEqual([]);
   });
 
-  it("rejects plugin names reserved by core features", async () => {
-    const briefsPlugin = defineJuniorPlugin({
-      manifest: {
-        name: "briefs",
-        displayName: "Briefs",
-        description: "Conflicting Briefs plugin",
-      },
-    });
-
-    await expect(
-      createApp({ plugins: defineJuniorPlugins([briefsPlugin]) }),
-    ).rejects.toThrow('Plugin registration name "briefs" is reserved by core');
-    expect(getPlugins()).toEqual([]);
-  });
-
   it("rejects invalid plugin names before mutating app config", async () => {
     await createApp({
       plugins: defineJuniorPlugins([]),
diff --git a/packages/junior/tests/unit/core-feature-registration.test.ts b/packages/junior/tests/unit/core-feature-registration.test.ts
new file mode 100644
index 0000000000..de1181974c
--- /dev/null
+++ b/packages/junior/tests/unit/core-feature-registration.test.ts
@@ -0,0 +1,41 @@
+import { defineJuniorPlugin } from "@sentry/junior-plugin-api";
+import { afterEach, describe, expect, it } from "vitest";
+import { setBriefsConfig } from "@/chat/briefs/registration";
+import {
+  allCoreFeatureRegistrations,
+  coreFeatureRegistrations,
+} from "@/chat/core-features/registration";
+import { validatePlugins } from "@/chat/plugins/agent-hooks";
+
+const briefsPlugin = defineJuniorPlugin({
+  manifest: {
+    name: "briefs",
+    displayName: "Briefs",
+    description: "Conflicting Briefs plugin",
+  },
+});
+
+afterEach(() => {
+  setBriefsConfig(undefined);
+});
+
+describe("core feature registration", () => {
+  it("enables Briefs from app config but keeps its registration available", () => {
+    expect(coreFeatureRegistrations()).toEqual([]);
+    expect(
+      allCoreFeatureRegistrations().map((feature) => feature.manifest.name),
+    ).toEqual(["briefs"]);
+
+    setBriefsConfig({ enabled: true });
+
+    expect(
+      coreFeatureRegistrations().map((feature) => feature.manifest.name),
+    ).toEqual(["briefs"]);
+  });
+
+  it("reserves core feature names", () => {
+    expect(() => validatePlugins([briefsPlugin])).toThrow(
+      'Plugin registration name "briefs" is reserved by core',
+    );
+  });
+});