fix(cli): cdk list pollutes stdout with synthesis time

[sai-ray]

Fixes #1632

cdk list prints ✨ Synthesis time: X.XXs to stdout in CI mode (regressed in 2.1127.0). That extra line shows up in machine-readable output, so piping cdk list into a parser (e.g. cdk list --json | jq) breaks.

For example, $ cdk list --json in CI mode gives you:

✨  Synthesis time: 3.72s
MyStack

The parser only expects the stack list, so the Synthesis time line makes it fail.

#1603 routed cdk list through the toolkit-lib list action, which synthesizes via synthAndMeasure. That helper opens a timing span, and ending the span emits CDK_TOOLKIT_I1000 ("Synthesis time"). In CI mode the CLI sends non-error messages to stdout, so the line lands next to the listing.

The CLI now drops the synth-time message (CDK_TOOLKIT_I1000) on the list path before it's written, so stdout carries only the listing.

$ cdk list --json # after fix, CI mode

MyStack

Testing

• Unit test: cdk list registers a one-shot suppressor for CDK_TOOLKIT_I1000, so the synth-time line is not printed.
• Integ test: cdk ls in CI produces stdout with only the stack listing, no synthesis-time line.
• Verified manually against a sample app (cdk list --json in CI → clean stdout).

Checklist

• This change contains a major version upgrade for a dependency and I confirm all breaking changes are addressed
  • Release notes for the new version:

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

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[rix0rrr]

I would say this is the wrong fix.

Wouldn't it make more sense to suppress the "synthesis time" message in --json mode, or something to that effect?

Either that, or say "this is query and therefore we're not printing anything other than the output" (which you said on Slack that I also like), but I wouldn't implement that by bypassing the entire method synthAndMeasure method; all synths get routed through that function and I would like to keep it that way. The measuring is NOT JUST printing to the screen, it's also measuring internally.

Maybe we suppress printing by the the IoHost instead or something.

This fix should be about what gets printed, not about what gets done.

[mrgrain]

+100

[sai-ray]

Updated to follow the same pattern as the rewriteOnce(I2901) line right above, a host-side listener on a library message. That one reshapes the listing, this one suppresses the synth-time line via once(I1000, () => ({ preventDefault: true })). synthAndMeasure stays untouched so synth is still measured, only what's printed changes.

[mrgrain]

+100