Add AI coding guidance documentation

AGENTS.md

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+# AGENTS.md
+
+Guidance for AI coding agents working in this repository.
+
+## Project
+
+`flutter_future_progress_dialog` — a published pub.dev package (Nerdy Pro) that shows a modal progress dialog while a `Future` runs and returns the result as a sealed `ProgressDialogResult<T>`. Pure Dart/Flutter library, no platform channels or native code.
+
+## Commands
+
+```shell
+flutter pub get                                  # run in both root and example/ — analyze covers example/ and errors out without its deps
+dart analyze --fatal-infos                       # CI gate — infos fail the build, not just warnings
+flutter test                                     # full suite
+flutter test test/progress_dialog_test.dart      # single file
+flutter test --plain-name 'completes with some error'   # single test by name
+flutter pub publish --dry-run                    # CI gate — checks package metadata/pubignore
+cd example && flutter run                        # demo app (Material / Cupertino / custom / failure buttons)
+```
+
+Do not run `dart format .` — the codebase is formatted at ~120 columns while `dart format` defaults to 80, so it rewrites nearly every file. No format check runs in CI.
+
+## Architecture
+
+Everything lives in `lib/src/`; `lib/flutter_future_progress_dialog.dart` is the barrel and exports **only** `src/result.dart` and `src/show_progress_dialog.dart`. `ProgressBarDialog` and `CupertinoProgressBarDialog` are intentionally not part of the public API — a new file in `lib/src/` is invisible to consumers until added to the barrel.
+
+### Dialog lifecycle (the non-obvious part)
+
+`lib/src/show_progress_dialog.dart` does not call `showDialog`. It constructs the route itself so the route object can be captured in a `late final` and referenced from the builder:
+
+1. `NavigatorState` is resolved **before** any `await` and passed into `_callback` — the dialog's `BuildContext` may be unmounted by the time the task finishes (fixed in 1.5.0, regression-tested).
+2. A `DialogRoute` / `CupertinoDialogRoute` is pushed manually with `barrierDismissible: false`; Material also carries `InheritedTheme.capture(...)` so themes survive crossing into the root navigator.
+3. The route's child is wrapped in `ExactlyOnce` (`lib/src/exactly_once.dart`), which fires the task from a post-frame callback guarded by a `Completer` — `build` runs many times during the dialog animation, so this guarantees the future starts exactly once.
+4. On completion, `_callback` checks `route.isActive` and closes via `navigator.removeRoute(route, result)` — deliberately **not** `Navigator.pop()` (changed in 1.4.2), so a route someone else pushed on top is never popped by mistake.
+5. `showProgressDialog` force-unwraps the push future (`result!`); it relies on `removeRoute` always supplying a result, so any change to step 4 must preserve that.
+
+Errors never escape: the private `Task<T>.result()` extension wraps the call in try/catch and converts to `Success` / `Failure`.
+
+`showAdaptiveProgressDialog` branches on `dart:io` `Platform.isMacOS || Platform.isIOS`, which means the adaptive entry point is **not web-safe**; the Material and Cupertino entry points are.
+
+### Result type
+
+`lib/src/result.dart` is a `sealed class ProgressDialogResult<T>` with `Success<T>` / `Failure<T>` subclasses, both with value equality. Exhaustive `switch` on it is the documented usage pattern, so adding a third variant is a breaking API change for every consumer.
+
+### Testing
+
+Widget tests drive the dialog through a `SchedulerBinding.addPostFrameCallback` + `Completer` pattern rather than tapping. `pumpAndSettle` hangs while a task is in flight (the dialog animates indefinitely), so tests that must observe the mid-flight state pump exactly two frames manually — one to build, one to fire `ExactlyOnce`.
+
+## Release
+
+Version lives in `pubspec.yaml` with a matching `CHANGELOG.md` entry. Publishing is the manual `workflow_dispatch` workflow in `.github/workflows/publish.yaml`, which runs tests then publishes via OIDC through the `pub_publish` GitHub environment (approval-gated). `example/` is shipped to pub.dev; `.pubignore` excludes `img/`, build output, and IDE files.

CLAUDE.md

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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+See @AGENTS.md — it is the single source of truth for commands, architecture, and release process. Keep changes there, not here.