fix: show inputs on ENTER and add selected state styling

[nborges-aws]

Description

Two consistency fixes in the TUI to bring screens in harness create/update and project create inline with the rest of the codebase.

• harness -> create/update -> memory: Input field previously appeared immediately on hover. And no select state was present. With update, user must click enter for input to appear. Selection now has styling, and on return/esc value in input field is persisted.
• harness -> create/update -> prompt: uses FormTextArea component, which is a multi-line version of FormTextInput. However, the are component was missing the styling applied to the form input component. This PR aligns the styling between the two for consistency

Before

Screen.Recording.2026-09-04.at.4.43.46.PM.mov

After

Screen.Recording.2026-09-04.at.4.44.48.PM.mov

Type of Change

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

Testing

How have you tested the change?

• bun run test (x pass, 0 fail)
• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

---

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[agentcore-devx-automation]

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

[agentcore-devx-automation]

AgentCore Harness Review

Verdict: Looks good

Nice cleanup. The PR does three cohesive things:

• FormTextArea: replaces the top-only divider with a rounded box around the editable content and colors it with theme.colors.focus when focused. Reads clearly.
• PromptStep: drops the border box around the char counter — good simplification.
• ModelStep (project create) and MemoryStep byo (harness create/update): hides the dependent text field(s) until the user confirms the radio choice with enter, and shows a "selected" indicator on the radio while editing. This matches the existing ToolsStep pattern, and the new update test that verifies the current byo ARN isn't revealed until enter is a nice privacy touch.

I checked the ScrollView interaction in ModelStep — keepFocusedFieldVisible re-runs when focusedField changes, and onItemHeightChange will fire when fields mount/unmount, so hiding the fields until enter doesn't break scrolling.

Tests exercise the real components end-to-end via renderScreen — no additional mocking introduced. No new user-facing feature that would need telemetry, so nothing missing there either.

Looks good to merge.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.99%. Comparing base (535785c) to head (b71bcc9).
⚠️ Report is 1 commits behind head on refactor.

Additional details and impacted files

@@            Coverage Diff            @@
##           refactor    #2238   +/-   ##
=========================================
  Coverage     96.98%   96.99%           
=========================================
  Files           564      564           
  Lines         39221    39216    -5     
=========================================
- Hits          38040    38039    -1     
+ Misses         1181     1177    -4     

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