fix(cli): --yes mode requires a TTY when a request's default is falsy

[Adityaj0]

Reason for this change

CliIoHost.resolveRequest's --yes auto-respond path used a truthy check (if (msg.defaultResponse)) before returning the request's default response. Non-boolean prompts (booleans are handled separately via isConfirmationPrompt) whose default is falsy-but-valid — an empty string '' or the number 0 — fail this check and fall through to the isTTY gate, throwing TtyNotAttached instead of using the default, even though --yes was passed specifically so the CLI wouldn't need a TTY.

This is inconsistent with the sibling NonInteractiveIoHost implementation, which handles the boolean case separately and then unconditionally returns msg.defaultResponse — the intended semantics CliIoHost's --yes mode is supposed to mirror.

Two real call sites already pass an empty-string default and are affected today:

• cdk import's per-property resource-identifier prompt (importer.ts) — empty default means "skip this identifier"
• The SDK's MFA-token prompt (awscli-compatible.ts, CDK_SDK_I1100)

So cdk import --yes (or any non-interactive/CI run hitting one of these prompts) currently aborts with TtyNotAttached instead of silently taking the default.

Description of changes

Changed the truthy check to a definedness check: if (msg.defaultResponse !== undefined), mirroring the typeof ... === 'string' || 'number' checks already used a few lines below in isPromptableRequest.

Description of how you validated changes

Added a regression test in cli-io-host.test.ts that constructs a CliIoHost with autoRespond: true, isTTY: false and asserts that requests with defaultResponse: '' and defaultResponse: 0 resolve to those values instead of throwing. Verified the test fails with TtyNotAttached against the old code and passes with the fix. Ran the full cli-io-host test suite (91 tests) — all pass.

Checklist

• Unit tests added/updated
• Integration tests added/updated (if deploying new resource types or cross-service interactions) — not applicable, no AWS resource interaction
• No manual edits to generated files

---

Fixes #1891

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

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.34%. Comparing base (ca8a14a) to head (d70fe1d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1892      +/-   ##
==========================================
- Coverage   91.38%   91.34%   -0.04%     
==========================================
  Files          80       80              
  Lines       12264    12264              
  Branches     1747     1746       -1     
==========================================
- Hits        11207    11203       -4     
- Misses       1021     1025       +4     
  Partials       36       36              

Flag	Coverage Δ
suite.unit	91.34% <100.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.