Mark AnsiCode and AnsiCodeType final

[natebosch]

As discussed in #2297

Eagerly mark these as final to disallow implements before landing
changes to the API.

An internal test run confirmed no google3 use cases rely on the
capability.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:bazel_worker	1.1.5	already published at pub.dev
package:benchmark_harness	2.4.0	already published at pub.dev
package:boolean_selector	2.1.2	already published at pub.dev
package:browser_launcher	1.2.0-wip	WIP (no publish necessary)
package:cli_config	0.2.1-wip	WIP (no publish necessary)
package:cli_util	0.5.1	already published at pub.dev
package:clock	1.1.3-wip	WIP (no publish necessary)
package:code_builder	4.12.0-wip	WIP (no publish necessary)
package:coverage	1.15.0	already published at pub.dev
package:csslib	1.0.2	already published at pub.dev
package:extension_discovery	2.1.0	already published at pub.dev
package:file	7.0.2-wip	WIP (no publish necessary)
package:file_testing	3.1.0-wip	WIP (no publish necessary)
package:glob	2.1.3	already published at pub.dev
package:graphs	2.4.0-wip	WIP (no publish necessary)
package:html	0.15.7-wip	WIP (no publish necessary)
package:io	1.1.0-wip	WIP (no publish necessary)
package:json_rpc_2	4.1.0	already published at pub.dev
package:markdown	7.4.0	ready to publish	markdown-v7.4.0
package:mime	2.1.0-wip	WIP (no publish necessary)
package:oauth2	2.0.5	already published at pub.dev
package:package_config	2.3.0-wip	WIP (no publish necessary)
package:pool	1.5.3-wip	WIP (no publish necessary)
package:process	5.0.5	(error) pubspec version (5.0.5) and changelog (5.0.6-wip) don't agree
package:pub_semver	2.2.0	already published at pub.dev
package:pubspec_parse	1.6.0-wip	WIP (no publish necessary)
package:source_map_stack_trace	2.1.3-wip	WIP (no publish necessary)
package:source_maps	0.10.14-wip	WIP (no publish necessary)
package:source_span	1.10.2	already published at pub.dev
package:sse	4.2.0	already published at pub.dev
package:stack_trace	1.12.2-wip	(error) pubspec version (1.12.2-wip) and changelog (1.12.2-dev) don't agree
package:stream_channel	2.1.4	already published at pub.dev
package:stream_transform	2.1.2-wip	WIP (no publish necessary)
package:string_scanner	1.4.2-wip	WIP (no publish necessary)
package:term_glyph	1.2.3-wip	WIP (no publish necessary)
package:test_reflective_loader	0.6.0	ready to publish	test_reflective_loader-v0.6.0
package:timing	1.0.2	already published at pub.dev
package:unified_analytics	8.0.15	ready to publish	unified_analytics-v8.0.15
package:watcher	1.2.2-wip	WIP (no publish necessary)
package:yaml	3.1.4-wip	WIP (no publish necessary)
package:yaml_edit	2.2.4	already published at pub.dev

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

PR Health

License Headers ✔️

// Copyright (c) 2026, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

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no missing headers

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Unrelated files missing license headers

Files
pkgs/bazel_worker/benchmark/benchmark.dart
pkgs/coverage/lib/src/coverage_options.dart
pkgs/html/example/main.dart
pkgs/pubspec_parse/test/git_uri_test.dart
pkgs/watcher/test/custom_watcher_factory_test.dart

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Unused Dependencies ✔️

Package	Status
io	✔️ All dependencies utilized correctly.

For details on how to fix these, see dependency_validator.

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Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

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Coverage ✔️

File	Coverage
pkgs/io/lib/src/ansi_code.dart	💚 85 %

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Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
io	Non-Breaking	1.0.5	1.1.0-wip	1.1.0-wip	✔️

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API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

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[gemini-code-assist]

Code Review

This pull request marks the AnsiCode and AnsiCodeType classes as final to explicitly prevent subclassing and interface implementation, ensuring future API flexibility. These changes are documented in the CHANGELOG as potentially breaking. Feedback was provided to correct a grammatical error in the CHANGELOG description for better readability.

[gemini-code-assist]

The phrasing "never intended" is missing a verb. It should be "were never intended" to correctly describe the intent behind the classes.

Suggested change

	never intended to support subclasses and were already closed for extension
	were never intended to support subclasses and were already closed for extension