fix(dev): support Node tool shims on Windows

[aidandaly24]

Description

Fixes the two consecutive Windows failures that prevent TypeScript CodeZip agents from starting
under agentcore dev.

On Windows, npm package commands are commonly .cmd shims and cannot be launched directly through
Node's spawn APIs. The dev server previously raw-spawned both npm install and
npx tsx watch .... The install failure also discarded the process creation error and displayed
unknown error; manually installing dependencies only advanced the flow to the same
spawn npx ENOENT failure.

This change:

• runs npm, pnpm, and yarn installation through the existing Windows-aware subprocess helper
• launches npx tsx watch through the platform shell on Windows while preserving direct spawning
  on POSIX
• retains process creation errors in captured stderr instead of reporting unknown error
• writes browser-mode agent messages to the advertised dev log as well as the display callback
• adds regression coverage for Windows command routing, install failures, subprocess diagnostics,
  and web-UI log persistence

Related Issue

Closes #1849
Closes #2036

Documentation PR

N/A. This restores the documented TypeScript development workflow on Windows.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• N/A - no src/assets/ files were modified

Additional verification:

• npm run build
• npm run format:check
• Focused dev/subprocess tests: 56 passed
• Full unit suite: 6,115 passed
• Integration tests: 336 passed, 1 skipped
• Windows behavior is covered through platform-mode unit tests; no Windows host was available for
  local end-to-end execution

Checklist

• I have read the CONTRIBUTING document
• I have added necessary tests that prove the fix is effective
• No documentation change is required
• No new example is required
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

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terms of your choice.

[github-actions]

Package Tarball

aws-agentcore-0.27.1.tgz

How to install

gh release download pr-2054-tarball --repo aws/agentcore-cli --pattern "*.tgz" --dir /tmp/pr-tarball
npm install -g /tmp/pr-tarball/aws-agentcore-0.27.1.tgz

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)

[Hweinstock]

is there any way we can get a windows env to test this? want to make sure we're good to unblock #2050 (comment).

[jariy17]

I verified this works with a Windows Environment. However, we should look into using cross-spawn. It handles platform specific behaviors for us like converting file path into Windows compatible path. We should use this in the refactor dev one when we can.