feat(analytics): add trackScreenView and trackScreenLeave public APIs

[rahul-mixpanel]

Summary

• Adds mixpanel.autocapture.trackScreenView(screenName, properties?) and mixpanel.autocapture.trackScreenLeave(screenName, properties?) public APIs, mirroring the native Android/Swift SDK interfaces
• Implements platform channel handlers for Android (getAutocapture().trackScreenView/trackScreenLeave) and iOS/macOS (autocapture.trackScreenView/trackScreenLeave)
• Adds web fallback implementation (tracks $mp_page_view / $mp_page_leave with current_page_title and $mp_autocapture properties)
• Bumps native SDK dependencies: Android mixpanel-android 8.7.0 → 8.9.0, iOS/macOS Mixpanel-swift 6.4.1 → 6.5.0
• Updates example app with MixpanelNavigatorObserver for automatic screen tracking

Changes

• lib/mixpanel_flutter.dart — New Autocapture class with lazy getter on Mixpanel
• android/.../MixpanelFlutterPlugin.java — handleTrackScreenView and handleTrackScreenLeave methods
• swift/Classes/SwiftMixpanelFlutterPlugin.swift — Swift handler implementations
• lib/mixpanel_flutter_web.dart — Web fallback implementation
• android/build.gradle — Bump mixpanel-android to 8.9.0
• ios/mixpanel_flutter.podspec — Bump Mixpanel-swift to 6.5.0
• macos/mixpanel_flutter.podspec — Bump Mixpanel-swift to 6.5.0
• example/lib/main.dart — NavigatorObserver-based screen tracking

Test plan

• All 129 unit tests pass
• Manual test on Android — verify $mp_page_view and $mp_page_leave events fire on navigation
• Manual test on iOS — verify events fire on navigation
• Verify current_page_title and $mp_autocapture properties are set by native SDK (not duplicated in Dart layer)

Closes SDK-120

[linear-code]

SDK-120

[greptile-apps]

Confidence Score: 5/5

Safe to merge; all three platform paths route correctly and the Dart layer validates input before any channel call.

The implementation closely mirrors the existing People/FeatureFlags patterns. The two findings are minor: Android's missing screenName null-check is covered by the Dart-layer guard, and the unawaited futures are confined to the example app. No data-loss or crash path exists on the normal call flow.

The Android handler (MixpanelFlutterPlugin.java) and the example app's MixpanelNavigatorObserver are worth a second look.

Important Files Changed

Filename	Overview
packages/mixpanel_flutter/lib/mixpanel_flutter.dart	Adds Autocapture class with trackScreenView/trackScreenLeave and a lazy getter on Mixpanel; consistent with People/FeatureFlags patterns
packages/mixpanel_flutter/android/src/main/java/com/mixpanel/mixpanel_flutter/MixpanelFlutterPlugin.java	Adds handleTrackScreenView/handleTrackScreenLeave; screenName is not null-checked before native call, unlike the Swift counterpart
packages/mixpanel_flutter/swift/Classes/SwiftMixpanelFlutterPlugin.swift	Swift handlers use proper guard let safe-cast pattern with FlutterError on failure; consistent with rest of file
packages/mixpanel_flutter/lib/mixpanel_flutter_web.dart	Web fallback correctly tracks $mp_page_view/$mp_page_leave with SDK properties taking precedence; consistent with existing handler patterns
packages/mixpanel_flutter/example/lib/main.dart	Adds MixpanelNavigatorObserver for automatic screen tracking; unawaited futures in didPush/didPop silently swallow init/tracking errors
packages/mixpanel_flutter/ios/mixpanel_flutter.podspec	Bumps Mixpanel-swift dependency from 6.4.1 to 6.5.0
packages/mixpanel_flutter/android/build.gradle	Bumps mixpanel-android from 8.7.0 to 8.9.0

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant App as Flutter App
    participant AC as Autocapture (Dart)
    participant Ch as MethodChannel
    participant Android as Android Plugin
    participant iOS as Swift Plugin
    participant Web as Web Plugin

    App->>AC: trackScreenView(screenName)
    AC->>AC: isValidString check
    alt valid screenName
        AC->>Ch: invokeMethod("trackScreenView")
        alt Android path
            Ch->>Android: handleTrackScreenView
            Android->>Android: build JSONObject + getMergedProperties
            Android->>Android: getAutocapture().trackScreenView
            Android-->>Ch: result.success(null)
        else iOS/macOS path
            Ch->>iOS: handleTrackScreenView
            iOS->>iOS: guard screenName non-empty
            iOS->>iOS: autocapture.trackScreenView
            iOS-->>Ch: result(nil)
        else Web path
            Ch->>Web: handleTrackScreenView
            Web->>Web: merge props, SDK props win
            Web->>Web: track("$mp_page_view")
            Web-->>Ch: null
        end
        Ch-->>AC: void
    else invalid screenName
        AC-->>App: silent no-op
    end

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%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
    participant App as Flutter App
    participant AC as Autocapture (Dart)
    participant Ch as MethodChannel
    participant Android as Android Plugin
    participant iOS as Swift Plugin
    participant Web as Web Plugin

    App->>AC: trackScreenView(screenName)
    AC->>AC: isValidString check
    alt valid screenName
        AC->>Ch: invokeMethod("trackScreenView")
        alt Android path
            Ch->>Android: handleTrackScreenView
            Android->>Android: build JSONObject + getMergedProperties
            Android->>Android: getAutocapture().trackScreenView
            Android-->>Ch: result.success(null)
        else iOS/macOS path
            Ch->>iOS: handleTrackScreenView
            iOS->>iOS: guard screenName non-empty
            iOS->>iOS: autocapture.trackScreenView
            iOS-->>Ch: result(nil)
        else Web path
            Ch->>Web: handleTrackScreenView
            Web->>Web: merge props, SDK props win
            Web->>Web: track("$mp_page_view")
            Web-->>Ch: null
        end
        Ch-->>AC: void
    else invalid screenName
        AC-->>App: silent no-op
    end

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