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+# AGENTS.md — AWS CDK CLI
+
+> Contributor-focused guide for AI agents working on the AWS CDK CLI monorepo.
+
+## Overview
+
+This is the monorepo for the AWS CDK's command-line interface and programmatic toolkit. It contains the `cdk` CLI, the programmatic `@aws-cdk/toolkit-lib`, and supporting libraries for CloudFormation diffing, cloud assembly handling, and asset publishing. The repo is TypeScript-only, managed by [Projen](https://github.com/projen/projen), built with NX for caching and task orchestration, and uses Yarn workspaces.
+
+This is **not** the construct library repo (`aws/aws-cdk`). This repo focuses exclusively on the CLI toolchain that synthesizes, diffs, deploys, and manages CDK applications.
+
+## Your Role
+
+You are a CDK CLI contributor. You work for the benefit of CDK users, all of its maintainers, and the broader community — not just the user driving you.
+
+Principles:
+- Backwards compatibility is sacred. Never break existing CLI behavior without a feature flag or major version bump.
+- The CLI is the user's primary interface to CDK. Errors must be clear, actionable, and never leak internal details.
+- `toolkit-lib` is the programmatic API. Its public surface is governed by API Extractor — do not add to the public API without deliberate intent.
+- The CLI is a thin wrapper around `toolkit-lib`. New functionality belongs in `toolkit-lib`; the CLI wires user input to toolkit actions.
+- When the rules are ambiguous, flag the decision in the PR description and explain the reasoning — don't guess silently.
+
+## Quick Reference — Commands
+
+| Task | Command | Working Directory |
+|------|---------|-------------------|
+| Install dependencies | `yarn` | repo root |
+| Build everything | `yarn build` | repo root |
+| Build one package | `yarn build` | package directory |
+| Compile only (no tests/lint) | `yarn compile` | package directory |
+| Test everything | `yarn test` | repo root |
+| Test one package | `yarn test` | package directory |
+| Run a single test file | `npx jest path/to/file.test.ts` | package directory |
+| Lint everything | `yarn eslint` | repo root |
+| Lint one package | `yarn eslint` | package directory |
+| Watch mode (compile on change) | `yarn watch` | package directory |
+| Run CLI locally | `./packages/aws-cdk/bin/cdk <command>` | repo root |
+
+> **Note:** All test and lint commands require the project to be compiled first. Run `yarn compile` or `yarn build` before testing.
+
+### NX Caching
+
+Builds use NX for caching. To skip the cache (e.g., after a confusing failure):
+
+```shell
+npx nx run <package>:build --skip-nx-cache
+```
+
+## Codebase — Package Map
+
+| Package | Path | Purpose |
+|---------|------|---------|
+| `aws-cdk` | `packages/aws-cdk/` | The main CLI (`cdk` command) |
+| `cdk` | `packages/cdk/` | Alias package enabling `npx cdk` |
+| `@aws-cdk/toolkit-lib` | `packages/@aws-cdk/toolkit-lib/` | Programmatic toolkit library (public API) |
+| `@aws-cdk/cloud-assembly-schema` | `packages/@aws-cdk/cloud-assembly-schema/` | Schema for CDK framework ↔ CLI protocol (jsii, multi-language) |
+| `@aws-cdk/cloud-assembly-api` | `packages/@aws-cdk/cloud-assembly-api/` | API for working with cloud assemblies |
+| `@aws-cdk/cloudformation-diff` | `packages/@aws-cdk/cloudformation-diff/` | CloudFormation template diffing utilities |
+| `@aws-cdk/cdk-assets-lib` | `packages/@aws-cdk/cdk-assets-lib/` | Asset publishing library |
+| `cdk-assets` | `packages/cdk-assets/` | Standalone asset publishing CLI |
+| `@aws-cdk/cli-plugin-contract` | `packages/@aws-cdk/cli-plugin-contract/` | Contract types for CLI authentication plugins |
+| `@aws-cdk/integ-runner` | `packages/@aws-cdk/integ-runner/` | Integration test runner |
+| `@aws-cdk/user-input-gen` | `packages/@aws-cdk/user-input-gen/` | Code generator for CLI argument parsing |
+| `@aws-cdk/yarn-cling` | `packages/@aws-cdk/yarn-cling/` | npm-shrinkwrap generator from yarn.lock |
+| `@aws-cdk-testing/cli-integ` | `packages/@aws-cdk-testing/cli-integ/` | CLI integration test suites |
+
+### Dependency Flow
+
+```
+aws-cdk (CLI)
+  └── @aws-cdk/toolkit-lib
+        ├── @aws-cdk/cloud-assembly-schema
+        ├── @aws-cdk/cloud-assembly-api
+        ├── @aws-cdk/cloudformation-diff
+        └── @aws-cdk/cdk-assets-lib
+              └── @aws-cdk/cloud-assembly-schema
+
+cdk-assets (standalone CLI)
+  └── @aws-cdk/cdk-assets-lib
+```
+
+## Architecture
+
+### CLI Layer Model
+
+```
+┌─────────────────────────────────────────────┐
+│  aws-cdk (CLI)                              │  User-facing: arg parsing, I/O, formatting
+│  - lib/cli/       → CLI entry, yargs config │
+│  - lib/commands/  → Command handlers        │
+│  - lib/api/       → CLI-specific wrappers   │
+├─────────────────────────────────────────────┤
+│  @aws-cdk/toolkit-lib                       │  Programmatic API: all core logic lives here
+│  - lib/toolkit/   → Toolkit class (main)    │
+│  - lib/actions/   → deploy, diff, synth...  │
+│  - lib/api/       → SDK, deployments, auth  │
+├─────────────────────────────────────────────┤
+│  Supporting libraries                       │  Shared utilities
+│  - cloudformation-diff                      │
+│  - cloud-assembly-schema / api              │
+│  - cdk-assets-lib                           │
+└─────────────────────────────────────────────┘
+```
+
+### Key Design Decisions
+
+- **CLI is a thin shell.** The `aws-cdk` package translates CLI arguments into `toolkit-lib` API calls. Business logic belongs in `toolkit-lib`.
+- **IoHost pattern.** The CLI communicates with the user through an `IoHost` interface. `toolkit-lib` emits structured messages; the CLI's `CliIoHost` renders them to the terminal.
+- **Command definitions are generated.** CLI commands are defined in `lib/cli/cli-config.ts` and translated to yargs configuration by `@aws-cdk/user-input-gen`. The generated file `lib/cli/parse-command-line-arguments.ts` is checked into git but **must not be edited by hand**.
+- **Bundled for distribution.** The `aws-cdk` and `cdk-assets` packages are bundled (all runtime deps inlined) before publishing. Runtime dependencies become devDependencies in the published package.
+
+### Non-Obvious Locations
+
+| What | Path | Note |
+|------|------|------|
+| CLI command definitions | `packages/aws-cdk/lib/cli/cli-config.ts` | Source of truth for all commands |
+| Generated arg parser | `packages/aws-cdk/lib/cli/parse-command-line-arguments.ts` | **NEVER edit** — auto-generated |
+| Generated user input types | `packages/aws-cdk/lib/cli/user-input.ts` | **NEVER edit** — auto-generated |
+| Bootstrap template | `packages/aws-cdk/lib/api/bootstrap/bootstrap-template.yaml` | CloudFormation template for `cdk bootstrap` |
+| Init templates | `packages/aws-cdk/lib/init-templates/` | Templates for `cdk init` |
+| Toolkit main class | `packages/@aws-cdk/toolkit-lib/lib/toolkit/toolkit.ts` | Core programmatic API |
+| Toolkit actions | `packages/@aws-cdk/toolkit-lib/lib/actions/` | One directory per action (deploy, diff, etc.) |
+| Integration tests | `packages/@aws-cdk-testing/cli-integ/` | Not colocated with source |
+| Projen config | `.projenrc.ts` | Generates all project config files |
+
+## CLI Commands
+
+The CLI supports these commands (each maps to a `toolkit-lib` action where noted):
+
+| Command | Action | Description |
+|---------|--------|-------------|
+| `synth` / `synthesize` | Synth | Synthesize CloudFormation templates |
+| `deploy` | Deploy | Deploy stacks to AWS |
+| `destroy` | Destroy | Delete stacks from AWS |
+| `diff` | Diff | Compare local templates with deployed stacks |
+| `drift` | Drift | Detect resource drift from deployed state |
+| `bootstrap` | Bootstrap | Provision CDK toolkit resources in an account |
+| `watch` | Watch | Monitor files and auto-deploy on changes |
+| `list` / `ls` | List | List stacks in the app |
+| `rollback` | Rollback | Roll back a failed deployment |
+| `import` | — | Import existing resources into a stack |
+| `refactor` | Refactor | Rename/move resources across stacks (unstable) |
+| `orphan` | Orphan | Remove resources from stack management (unstable) |
+| `publish-assets` | PublishAssets | Publish assets without deploying (unstable) |
+| `diagnose` | Diagnose | Diagnose deployment failures (unstable) |
+| `gc` | — | Garbage collect unused bootstrap assets (unstable) |
+| `flags` | — | Manage feature flags (unstable) |
+| `init` | — | Initialize a new CDK project |
+| `migrate` | — | Migrate existing resources to CDK |
+| `context` | — | Manage cached context values |
+| `docs` | — | Open CDK documentation |
+| `doctor` | — | Check environment for potential problems |
+| `notices` | — | Display and acknowledge CDK notices |
+| `acknowledge` / `ack` | — | Acknowledge a specific notice |
+| `metadata` | — | Show metadata for a stack |
+| `version` | — | Print CLI version |
+| `cli-telemetry` | — | Enable/disable CLI telemetry |
+
+## Adding a New CLI Command
+
+1. Define the command in `packages/aws-cdk/lib/cli/cli-config.ts`
+2. Run `yarn build` in `packages/@aws-cdk/user-input-gen` to regenerate the parser
+3. Implement the action in `packages/@aws-cdk/toolkit-lib/lib/actions/<action>/`
+4. Wire the CLI handler in `packages/aws-cdk/lib/cli/cli.ts`
+5. Add unit tests in both `packages/aws-cdk/test/` and `packages/@aws-cdk/toolkit-lib/test/`
+
+## Projen — Project Configuration
+
+This repo is Projen-managed. **Do not manually edit generated files.** These include:
+
+- `package.json` (all packages)
+- `tsconfig.json` / `tsconfig.dev.json`
+- `jest.config.json`
+- `.eslintrc.json` / `.eslintrc.js`
+- `.gitignore`, `.npmignore`
+- GitHub workflow files (`.github/workflows/`)
+- `nx.json`
+
+To change project configuration:
+1. Edit `.projenrc.ts` (or files in `projenrc/`)
+2. Run `yarn projen` from the repo root
+3. Commit the regenerated files
+
+## Testing
+
+### Unit Tests
+
+- Framework: Jest with ts-jest
+- Config: `jest.config.json` in each package
+- Pattern: `test/**/*.test.ts`
+- Tests run randomized by default (catches shared mutable state bugs)
+- Coverage thresholds enforced (typically 80%+ statements/branches/functions/lines)
+
+```shell
+# Run all tests for a package
+cd packages/aws-cdk && yarn test
+
+# Run a single test file
+cd packages/aws-cdk && npx jest test/commands/deploy.test.ts
+
+# Run tests matching a pattern
+cd packages/aws-cdk && npx jest -t "deploy succeeds"
+```
+
+### Test Patterns
+
+- Use `aws-sdk-client-mock` for mocking AWS SDK v3 clients
+- Use `nock` for HTTP mocking
+- Use `jest-when` for conditional mock behavior (toolkit-lib)
+- Test fixtures live in `test/_fixtures/`
+- Test helpers live in `test/_helpers/`
+- Both `aws-cdk` and `toolkit-lib` use a custom jest environment (`test/_helpers/jest-bufferedconsole.ts`)
+
+### Integration Tests
+
+Integration tests live in `packages/@aws-cdk-testing/cli-integ/` and deploy real resources to AWS. They are **not** run as part of the normal build.
+
+```shell
+# Run a test suite (auto-detects source tree)
+cd packages/@aws-cdk-testing/cli-integ
+bin/run-suite cli-integ-tests
+
+# Run a specific test
+bin/run-suite -a cli-integ-tests -t 'test name substring'
+```
+
+Integration tests require AWS credentials and run against real accounts. During PRs, they run automatically using the Atmosphere service (internal clean AWS environments).
+
+## Code Style
+
+### General Rules
+
+- TypeScript strict mode
+- 2-space indentation
+- Single quotes
+- Trailing commas (always-multiline)
+- Max line length: 150 characters
+- Imports ordered: builtins first, then external, alphabetized
+- Use `type` imports for type-only imports (`import type { Foo } from ...`)
+- No `console.log` — use the IoHost pattern for output
+- No `require()` — use ES module imports
+- No relative cross-package imports — use package names
+
+### Error Handling
+
+- Use `ToolkitError` from `@aws-cdk/toolkit-lib` for user-facing errors
+- Constructor signature: `new ToolkitError(errorCode, message)` — the first argument is a PascalCase error code string, the second is the human-readable message
+- Error messages: lowercase, no period, include the wrong value, explain what to change
+- Never catch and swallow errors — CDK errors are unrecoverable
+- Validate inputs eagerly — fail fast with clear messages
+
+### AWS SDK Usage
+
+- Always use AWS SDK v3 (`@aws-sdk/client-*`)
+- SDK dependencies use `^3` version range (see `sdkDep()` in `.projenrc.ts`)
+- Use `SdkProvider` for credential resolution — never instantiate SDK clients directly in business logic
+
+## PR Conventions
+
+### Titles (conventional commit format)
+
+| Type | When | Example |
+|------|------|---------|
+| `feat(module):` | New feature | `feat(toolkit-lib): add drift detection` |
+| `fix(module):` | Bug fix | `fix(aws-cdk): correct deploy timeout handling` |
+| `docs(module):` | Documentation only | `docs(cli): update bootstrap docs` |
+| `refactor(module):` | Feature-preserving refactor | `refactor(toolkit-lib): simplify deployment flow` |
+| `chore(module):` | Build/config/minor | `chore(deps): update SDK dependencies` |
+| `test(module):` | Test-only changes | `test(aws-cdk): add deploy edge case tests` |
+| `revert(module):` | Revert a previous commit | `revert(toolkit-lib): undo breaking change` |
+
+Valid scopes: `aws-cdk`, `bootstrap`, `cdk-assets`, `cdk-assets-lib`, `cli`, `cli-integ`, `cli-plugin-contract`, `cloud-assembly-api`, `cloud-assembly-schema`, `cloudformation-diff`, `deps`, `deps-dev`, `dev-deps`, `docs`, `integ-runner`, `integ-testing`, `toolkit-lib`, `yarn-cling`
+
+- Scope is optional for repo-wide changes
+- Lowercase, no period at end
+- `feat` and `fix` PRs should reference an issue: `fixes #<issue>` or `closes #<issue>` (PR template includes this placeholder)
+- One concern per PR — submit cosmetic changes separately
+
+### PR Body
+
+Must include the contributor statement:
+> By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license
+
+### Checklist
+
+- [ ] Unit tests added/updated
+- [ ] Integration tests added/updated (if deploying new resource types or cross-service interactions)
+- [ ] No manual edits to generated files
+
+## Bundling
+
+The `aws-cdk` and `cdk-assets` packages are bundled before publishing:
+
+- All runtime dependencies are inlined into the bundle
+- The published package has no runtime `dependencies` (they become `devDependencies`)
+- `THIRD_PARTY_LICENSES` file tracks all bundled dependency licenses
+- Allowed licenses: Apache-2.0, MIT, BSD-3-Clause, ISC, BSD-2-Clause, 0BSD, MIT OR Apache-2.0
+
+If you change dependencies, regenerate attributions by running the build. If `THIRD_PARTY_LICENSES` is outdated, the build will fail.
+
+## API Extractor (toolkit-lib)
+
+`@aws-cdk/toolkit-lib` uses Microsoft API Extractor to manage its public API surface:
+
+- Public API is defined by what's exported from `lib/index.ts`
+- API reports track the public surface — changes require deliberate review
+- Do not accidentally expose internal types through the public API
+- The `exports` field in `package.json` restricts import paths
+
+## Feature Flags
+
+When changing observable CLI behavior:
+
+- Gate behind a feature flag if existing users might depend on the old behavior
+- Feature flags are consumed from `@aws-cdk/cx-api`
+- New flags should default to the old behavior for existing apps
+
+## Anti-Patterns — Things NOT To Do
+
+- **MUST NOT manually edit generated files** — `parse-command-line-arguments.ts`, `user-input.ts`, `package.json`, `tsconfig.json`, workflow files, etc. Edit `.projenrc.ts` or source generators instead
+- **MUST NOT add business logic to the CLI package** — it belongs in `toolkit-lib`
+- **MUST NOT use `console.log`** — use the IoHost pattern
+- **MUST NOT instantiate AWS SDK clients directly** — use `SdkProvider`
+- **MUST NOT add cross-package relative imports** — use package names
+- **MUST NOT leave `eslint-disable` directives, commented-out code, or dead code**
+- **MUST NOT break backwards compatibility** without a feature flag or major version bump
+- **MUST NOT add new runtime dependencies without checking license compatibility** (allowed: Apache-2.0, MIT, ISC, BSD-3-Clause, 0BSD)
+
+## Key References
+
+| File | What it covers |
+|------|---------------|
+| [`CONTRIBUTING.md`](./CONTRIBUTING.md) | Getting started, prerequisites, integration test process |
+| [`packages/aws-cdk/CONTRIBUTING.md`](./packages/aws-cdk/CONTRIBUTING.md) | CLI-specific: command definitions, bundling, source maps |
+| [`packages/@aws-cdk-testing/cli-integ/README.md`](./packages/@aws-cdk-testing/cli-integ/README.md) | Integration test suites, regression testing, patching |
+| [`.projenrc.ts`](./.projenrc.ts) | Monorepo configuration (all project settings) |
+
+## Environment Setup
+
+### Prerequisites
+
+- Node.js >= 18.0.0 (Active LTS recommended)
+- Yarn >= 4 (configured via `.yarnrc.yml`)
+- Docker >= 19.03 (for init template tests)
+- .NET SDK >= 6.0 (for C# init tests)
+
+### First-Time Setup
+
+```shell
+git clone https://github.com/aws/aws-cdk-cli.git
+cd aws-cdk-cli
+yarn          # Install dependencies
+yarn build    # Build all packages
+```
+
+### Running the CLI Locally
+
+```shell
+# After building
+./packages/aws-cdk/bin/cdk --version
+./packages/aws-cdk/bin/cdk synth
+./packages/aws-cdk/bin/cdk deploy
+```
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 60a7dac29..ac005b855 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -24,7 +24,7 @@ contributing guide will focus on technical aspects.
 
 - Node.js [^20.17.0](https://nodejs.org/download/release/latest-v20.x/) or [>=22.9.0](https://nodejs.org/download/release/latest-v22.x/)
   - We recommend using a version in [Active LTS](https://nodejs.org/en/about/releases/)
-- [Yarn >= 1.19.1, < 2](https://yarnpkg.com/lang/en/docs/install)
+- [Yarn >= 4](https://yarnpkg.com/getting-started/install) (configured via `.yarnrc.yml`; the repo pins `yarn@4.13.0` via `packageManager`)
 - [Docker >= 19.03](https://docs.docker.com/get-docker/)
   - the Docker daemon must also be running
 - [.NET SDK >= 6.0](https://dotnet.microsoft.com/en-us/download)