chore(App Starts): Add info why Sentry app starts can be longer (#13269)

* add info why Sentry app starts can be longer

* update flutter

* Apply suggestions from code review

---------

Co-authored-by: Krystof Woldrich <[email protected]>

Author: kahest

docs/platforms/android/tracing/instrumentation/automatic-instrumentation.mdx

@@ -126,9 +126,17 @@ The App Start Instrumentation provides insight into how long your application ta
 
 The SDK differentiates between a cold and a warm start, but doesn't track hot starts/resumes.
 
-- **Cold start**: A cold start refers to an app’s starting from scratch: the system’s process has not, until this start, created the app’s process. Cold starts happen in cases such as your app’s being launched for the first time since the device booted, or since the system killed the app.
+- **Cold start**: A cold start refers to an app's starting from scratch: the system's process has not, until this start, created the app's process. Cold starts happen in cases such as your app's being launched for the first time since the device booted, or since the system killed the app.
 - **Warm start**: A warm start encompasses some subset of the operations that take place during a cold start; at the same time, it represents more overhead than a hot start. For instance: The system evicts your app from memory, and then the user re-launches it. The process and the activity need to be restarted, but the task can benefit somewhat from the saved instance state bundle passed into `onCreate()`.
 
+<Alert>
+
+Sentry's App Start instrumentation aims to be as comprehensive and representative of the user experience as possible, and adheres to guidelines by the platform vendors. For this reason, App Starts reported by Sentry might be longer than what you see in other tools.
+
+For example, Sentry measures the duration from process start, including the time it takes for all Content Providers to complete, until the first frame is rendered to the user.
+
+</Alert>
+
 The SDK sets the Span operation to `app.start.cold` for _Cold start_ and `app.start.warm` for _Warm start_.
 
 The SDK uses the `SentryPerformanceProvider` (ContentProvider) creation time as the beginning of the app start and the first frame drawn as the end.

docs/platforms/apple/common/tracing/instrumentation/automatic-instrumentation.mdx

@@ -103,6 +103,14 @@ The SDK differentiates between a cold and a warm start, but doesn't track hot st
 - **Cold start**: App launched for the first time, after a reboot or update. The app is not in memory and no process exists.
 - **Warm start**: App launched at least once, is partially in memory, and no process exists.
 
+<Alert>
+
+Sentry's App Start instrumentation aims to be as comprehensive and representative of the user experience as possible, and adheres to guidelines by the platform vendors. For this reason, App Starts reported by Sentry might be longer than what you see in other tools.
+
+For example, Sentry measures the duration from process start, including the time before before runtime initialization and before the first application object is loaded, until the first frame is rendered to the user.
+
+</Alert>
+
 Since [sentry-cocoa 8.18.0](https://github.com/getsentry/sentry-cocoa/releases/tag/8.18.0) the SDK creates the following app start spans:
 
 - **Pre Runtime Init**: from the process start time to the runtime init.

docs/platforms/react-native/tracing/instrumentation/automatic-instrumentation.mdx

@@ -55,6 +55,12 @@ The SDK differentiates between a cold and a warm start, but doesn't track hot st
 
 Cold and warm start are Mobile Vitals, which you can learn about in the [full documentation](/product/insights/mobile/mobile-vitals).
 
+<Alert>
+
+Sentry's App Start instrumentation aims to be as comprehensive and representative of the user experience as possible, and adheres to guidelines by the platform vendors. For this reason, App Starts reported by Sentry might be longer than what you see in other tools. Read more on the [Apple App Start docs](/platforms/apple/guides/ios/tracing/instrumentation/automatic-instrumentation/#app-start-tracing) and [Android App Start docs](/platforms/android/tracing/instrumentation/automatic-instrumentation/#app-start-instrumentation).
+
+</Alert>
+
 ### Slow and Frozen Frames
 
 Unresponsive UI and animation hitches annoy users and degrade the user experience. Two measurements to track these types of experiences are slow frames and frozen frames. If you want your app to run smoothly, you should try to avoid both. The SDK adds these two measurements for the transactions you capture.

docs/product/insights/mobile/mobile-vitals/index.mdx

@@ -19,6 +19,13 @@ The definitions of cold start and warm start change slightly depending on the op
 - [Flutter](/platforms/dart/guides/flutter/tracing/instrumentation/automatic-instrumentation/#app-start-instrumentation)
 - [React Native](/platforms/react-native/tracing/instrumentation/automatic-instrumentation/#app-start-instrumentation)
 
+<Alert>
+
+Sentry's App Start instrumentation aims to be as comprehensive and representative of the user experience as possible, and adheres to guidelines by the platform vendors. For this reason, App Starts reported by Sentry might be longer than what you see in other tools. Read more on the [Apple App Start docs](/platforms/apple/guides/ios/tracing/instrumentation/automatic-instrumentation/#app-start-tracing) and [Android App Start docs](/platforms/android/tracing/instrumentation/automatic-instrumentation/#app-start-instrumentation).
+
+
+</Alert>
+
 In the example below, the detail view of a transaction displays the warm start measurement in the right sidebar.
 
 ![The event detail of a transaction with a warm start measurement.](./img/app-start-transaction.png)

includes/dart-integrations/app-start-instrumentation.mdx

@@ -31,7 +31,7 @@ When the SDK receives the start and end times of the app launch, the SDK:
 
 <Alert>
 
-While the SDK differentiates between cold and warm starts, it doesn't track hot starts/resumes.
+Sentry's App Start instrumentation aims to be as comprehensive and representative of the user experience as possible, and adheres to guidelines by the platform vendors. For this reason, App Starts reported by Sentry might be longer than what you see in other tools.
 
 </Alert>