Please ensure you have read the contribution guide before creating a pull request.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

N/A — no existing issue tracks this work.

2. Or, if no issue exists, describe the change:

Problem:
The JS variant of ADK lacks parity with the adk-python environment tools, missing
necessary functionality for agent local file manipulation and shell execution.

Solution:
Added Node.js parity environment tools (ExecuteTool, ReadFileTool,
WriteFileTool, EditFileTool) and a bundled EnvironmentToolset in
core/src/tools/environment/. The toolset also injects the
ENVIRONMENT_INSTRUCTION into the LLM system requests for bounded contextual
usage.

One deliberate deviation from adk-python, please read:
ExecuteTool requires an explicit tool confirmation before it runs a command.
adk-python's execute tool has no such gate, but it also does not run anything
itself: it delegates to BaseEnvironment.execute(), so "run on the host" is one
backend an embedder selects. This port collapses that seam into a hardcoded
child_process implementation behind workingDir: string, which makes host
execution the only option — a model-authored string becomes arbitrary code
execution on the machine running the agent, and cwd is not a boundary. The gate
uses the same mechanism RunSkillInlineScriptTool already uses on main for
model-provided scripts. Restoring the BaseEnvironment seam would be the better
long-term answer and is a reasonable follow-up.

All four tool classes carry @experimental, matching adk-python and reflecting
that they became public API here via core/src/common.ts and core/src/index.ts.
Each tool exports its result type (ExecuteResult, ReadFileResult,
WriteFileResult, EditFileResult) rather than returning the base class's
Promise<unknown>.

There are no any, as any, eslint-disable, @ts-ignore or @ts-expect-error
uses anywhere in this diff, in src/ or in the tests.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Added core/test/tools/environment/tools_test.ts, covering boundaries across
reading, writing, editing and shell execution, plus the confirmation gate and
literal-text matching in EditFile. Local run:

$ npx vitest run --project unit:core core/test/tools/environment/tools_test.ts

 ✓ |unit:core| core/test/tools/environment/tools_test.ts (32 tests) 216ms

 Test Files  1 passed (1)
      Tests  32 passed (32)

Manual End-to-End (E2E) Tests:

1. Build the workspace with npm run build.
2. Run npx vitest run --project unit:core core/test/tools/environment/tools_test.ts
   to exercise the tools against a temporary working directory.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

resolveAndValidatePath performs a lexical containment check. It rejects ..
and absolute-path arguments, but path.resolve/path.relative never touch the
filesystem, so a symlink inside workingDir that points elsewhere still resolves
through. That is intentional — reading through symlinks is necessary for real
workspace layouts such as the package links npm creates under node_modules — and
the docstring says so explicitly. It is not a sandbox; callers who need one should
point the tools at an isolated filesystem.

This branch also carries one small, independent fix commit:
fix(dev): output agent bundle in project .adk_build_cache for hoisted dependencies,
which changes dev/src/utils/agent_loader.ts to emit the compiled agent bundle into
a project-local .adk_build_cache directory instead of the system temp directory, so
that hoisted node_modules dependencies resolve correctly. Happy to split this into a
separate PR if reviewers prefer.