Add external data source signal sources (GitHub, Linear, Zendesk) (#1262)

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## Problem

Signal sources only supported session replay and LLM analytics. We want users to also pull in GitHub issues, Linear issues, and Zendesk tickets as signal sources - but these require connecting an external data source first (OAuth for GitHub/Linear, API key for Zendesk).

## Changes

## ![CleanShot 2026-03-16 at 20.12.52@2x.png](https://app.graphite.com/user-attachments/assets/118c5d6a-9a24-4482-9bd7-6c1d3f818801.png)

Changes, as described by Claude:

- Use `/api/projects/...` consistently for external data source schema updates (`updateExternalDataSchema`)
- Add new OAuth scopes for external data sources and bump scope version
- Build `DataSourceSetup` component with per-source setup flows (GitHub repo picker, Linear OAuth + polling, Zendesk credentials form)
- Extend `SignalSourceToggles` to show a "Connect" button for sources that need setup before they can be toggled
- Extract signal source management logic into `useSignalSourceManager` hook (replaces the old `signalSourceSelectionsStore` and the inline logic that was duplicated between settings and onboarding) + update `SignalsStep`, `SignalSourcesSettings`, and `useTutorialTour` to use the new hook

Author: Twixes

apps/code/src/renderer/api/posthogClient.ts

@@ -20,14 +20,34 @@ export type McpServerInstallation = Schemas.MCPServerInstallation;
 
 export interface SignalSourceConfig {
   id: string;
-  source_product: "session_replay" | "llm_analytics";
-  source_type: "session_analysis_cluster" | "evaluation";
+  source_product:
+    | "session_replay"
+    | "llm_analytics"
+    | "github"
+    | "linear"
+    | "zendesk";
+  source_type: "session_analysis_cluster" | "evaluation" | "issue" | "ticket";
   enabled: boolean;
   config: Record<string, unknown>;
   created_at: string;
   updated_at: string;
 }
 
+export interface ExternalDataSourceSchema {
+  id: string;
+  name: string;
+  should_sync: boolean;
+}
+
+export interface ExternalDataSource {
+  id: string;
+  source_type: string;
+  status: string;
+  // The generated `ExternalDataSourceSerializers` types this as `string`,
+  // but the actual API returns an array of schema objects
+  schemas?: ExternalDataSourceSchema[] | string;
+}
+
 function isObjectRecord(value: unknown): value is Record<string, unknown> {
   return typeof value === "object" && value !== null;
 }
@@ -199,8 +219,17 @@ export class PostHogAPIClient {
   async createSignalSourceConfig(
     projectId: number,
     options: {
-      source_product: "session_replay" | "llm_analytics";
-      source_type: "session_analysis_cluster" | "evaluation";
+      source_product:
+        | "session_replay"
+        | "llm_analytics"
+        | "github"
+        | "linear"
+        | "zendesk";
+      source_type:
+        | "session_analysis_cluster"
+        | "evaluation"
+        | "issue"
+        | "ticket";
       enabled: boolean;
       config?: Record<string, unknown>;
     },
@@ -254,6 +283,73 @@ export class PostHogAPIClient {
     return (await response.json()) as SignalSourceConfig;
   }
 
+  async listExternalDataSources(
+    projectId: number,
+  ): Promise<ExternalDataSource[]> {
+    const data = (await this.api.get(
+      "/api/projects/{project_id}/external_data_sources/",
+      {
+        path: { project_id: projectId.toString() },
+        query: {},
+      },
+    )) as unknown as { results?: ExternalDataSource[] } | ExternalDataSource[];
+    return Array.isArray(data) ? data : (data.results ?? []);
+  }
+
+  async createExternalDataSource(
+    projectId: number,
+    payload: {
+      source_type: string;
+      payload: Record<string, unknown>;
+    },
+  ): Promise<ExternalDataSource> {
+    const response = await this.api.post(
+      "/api/projects/{project_id}/external_data_sources/",
+      {
+        path: { project_id: projectId.toString() },
+        body: payload as unknown as Schemas.ExternalDataSourceSerializers,
+        withResponse: true,
+        throwOnStatusError: false,
+      },
+    );
+    if (!response.ok) {
+      const errorData = isObjectRecord(response.data)
+        ? (response.data as { detail?: string })
+        : {};
+      throw new Error(
+        errorData.detail ??
+          `Failed to create external data source: ${response.statusText}`,
+      );
+    }
+    return response.data as unknown as ExternalDataSource;
+  }
+
+  async updateExternalDataSchema(
+    projectId: number,
+    schemaId: string,
+    updates: { should_sync: boolean },
+  ): Promise<void> {
+    const urlPath = `/api/projects/${projectId}/external_data_schemas/${schemaId}/`;
+    const url = new URL(`${this.api.baseUrl}${urlPath}`);
+    const response = await this.api.fetcher.fetch({
+      method: "patch",
+      url,
+      path: urlPath,
+      overrides: {
+        body: JSON.stringify(updates),
+      },
+    });
+    if (!response.ok) {
+      const errorData = (await response.json().catch(() => ({}))) as {
+        detail?: string;
+      };
+      throw new Error(
+        errorData.detail ??
+          `Failed to update external data schema: ${response.statusText}`,
+      );
+    }
+  }
+
   async getTasks(options?: {
     repository?: string;
     createdBy?: number;