feat(init): add detect-sentry local-op for cross-language Sentry detection (#657)

## Summary

Adds a `detect-sentry` local-op so the server can delegate Sentry
detection to the CLI's existing `detectDsn()` instead of doing its own
JS-only file scanning. This is the CLI-side half of the fix for
getsentry/cli-init-api#30 — the server-side PR will simplify
`check-existing-sentry` to use this new operation.

## Changes

New `DetectSentryPayload` type and `detectSentry()` handler in the
local-ops dispatcher. The handler calls the existing DSN detector which
already scans source code, .env files, and env vars across all 140+
supported platforms.

Returns `{ status: "installed", signals: [...], dsn: "..." }` when a DSN
is found, or `{ status: "none", signals: [] }` otherwise.

## Test plan

- Existing local-ops tests pass (51/51)
- Server-side PR (getsentry/cli-init-api) has updated tests for the new
flow
- Manual: `sentry init` in a JS project (regression), then a Python/Go
project (new detection)

Closes getsentry/cli-init-api#30

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: betegon

src/lib/init/local-ops.ts

@@ -29,6 +29,7 @@ import { resolveOrgPrefetched } from "./prefetch.js";
 import type {
   ApplyPatchsetPayload,
   CreateSentryProjectPayload,
+  DetectSentryPayload,
   DirEntry,
   FileExistsBatchPayload,
   ListDirPayload,
@@ -324,6 +325,8 @@ export async function handleLocalOp(
         return await applyPatchset(payload, options.dryRun);
       case "create-sentry-project":
         return await createSentryProject(payload, options);
+      case "detect-sentry":
+        return await detectSentry(payload);
       default:
         return {
           ok: false,
@@ -789,6 +792,26 @@ export async function detectExistingProject(cwd: string): Promise<{
   return null;
 }
 
+async function detectSentry(
+  payload: DetectSentryPayload
+): Promise<LocalOpResult> {
+  const { detectDsn } = await import("../dsn/index.js");
+  const dsn = await detectDsn(payload.cwd);
+
+  if (!dsn) {
+    return { ok: true, data: { status: "none", signals: [] } };
+  }
+
+  const signals = [
+    `dsn: ${dsn.source}${dsn.sourcePath ? ` (${dsn.sourcePath})` : ""}`,
+  ];
+
+  return {
+    ok: true,
+    data: { status: "installed", signals, dsn: dsn.raw },
+  };
+}
+
 async function createSentryProject(
   payload: CreateSentryProjectPayload,
   options: WizardOptions

src/lib/init/types.ts

@@ -25,7 +25,8 @@ export type LocalOpPayload =
   | FileExistsBatchPayload
   | RunCommandsPayload
   | ApplyPatchsetPayload
-  | CreateSentryProjectPayload;
+  | CreateSentryProjectPayload
+  | DetectSentryPayload;
 
 export type ListDirPayload = {
   type: "local-op";
@@ -91,6 +92,15 @@ export type CreateSentryProjectPayload = {
   };
 };
 
+export type DetectSentryPayload = {
+  type: "local-op";
+  operation: "detect-sentry";
+  /** Human-readable spinner hint from the server (≤ 120 chars, sensitive values redacted). */
+  detail?: string;
+  cwd: string;
+  params: Record<string, never>;
+};
+
 export type LocalOpResult = {
   ok: boolean;
   error?: string;

src/lib/init/wizard-runner.ts

@@ -129,6 +129,8 @@ export function describeLocalOp(payload: LocalOpPayload): string {
       return "Listing directory...";
     case "create-sentry-project":
       return `Creating project "${payload.params.name}" (${payload.params.platform})...`;
+    case "detect-sentry":
+      return "Checking for existing Sentry setup...";
     default:
       return `${(payload as { operation: string }).operation}...`;
   }