Because no versions of pigeon match >26.0.1 <27.0.0 and pigeon 26.0.1 depends on analyzer >=6.0.0 <8.0.0, pigeon ^26.0.1 requires analyzer >=6.0.0 <8.0.0.
And because custom_lint >=0.8.1 depends on analyzer ^8.0.0, pigeon ^26.0.1 is incompatible with custom_lint >=0.8.1.

dev_dependencies:
  custom_lint: ^0.8.1
  pigeon: ^26.0.1

❯ flutter doctor -v
[✓] Flutter (Channel stable, 3.32.7, on macOS 15.6.1 24G90 darwin-x64, locale en-GB) [2.8s]
    • Flutter version 3.32.7 on channel stable at /Users/jasonelder/Documents/Flutter/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision d7b523b356 (9 weeks ago), 2025-07-15 17:03:46 -0700
    • Engine revision 39d6d6e699
    • Dart version 3.8.1
    • DevTools version 2.45.1

[✓] Android toolchain - develop for Android devices (Android SDK version 36.0.0) [8.0s]
    • Android SDK at /Users/jasonelder/Library/Android/sdk
    • Platform android-36, build-tools 36.0.0
    • ANDROID_HOME = /Users/jasonelder/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jbr/Contents/Home/bin/java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 21.0.7+-13880790-b1038.58)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 16.4) [5.4s]
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Build 16F6
    • CocoaPods version 1.16.2

[✓] Chrome - develop for the web [200ms]
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2025.1) [198ms]
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 21.0.7+-13880790-b1038.58)

[✓] IntelliJ IDEA Community Edition (version 2024.3.1.1) [194ms]
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart

[✓] Connected device (3 available) [11.3s]
    • SM T395 (mobile) • 5200cc794383b581 • android-arm    • Android 9 (API 28)
    • macOS (desktop)  • macos            • darwin-x64     • macOS 15.6.1 24G90 darwin-x64
    • Chrome (web)     • chrome           • web-javascript • Google Chrome 140.0.7339.133

[✓] Network resources [553ms]
    • All expected network resources are available.

• No issues found!