[sxlijin]

Summary

• hide a declared default expression once a default-capable argument is checked for an explicit value
• keep the declared default visible while the argument is unchecked and using its default
• preserve schema-specific placeholders for required arguments

Root cause

ArgsForm always forwarded param.defaultExpression as the native input placeholder, regardless of whether the argument was using its default or had been checked for an explicit value. An empty explicit string therefore looked like the declared default would be sent.

Playground UI

Before

After

Validation

• pnpm exec biome check pkg-playground/src/ArgsForm.tsx
• pnpm --filter @b/pkg-playground typecheck
• pnpm --filter @b/pkg-playground test (145 tests)
• pnpm --filter app-vscode-webview typecheck
• pnpm --filter app-promptfiddle typecheck
• pnpm --filter app-vscode-webview test:unit:run -- ExecutionPanel.strict-mode.test.tsx (22 tests)
• git diff --check

Linear: https://linear.app/boundaryml2/issue/B-1061/default-arg-ui-when-default-args-are-checked-the-placeholder-in-the

Summary by CodeRabbit

• Bug Fixes
  • Fixed parameter fields showing default-value placeholders even after an explicit value was entered.
  • Placeholders now correctly reflect whether a parameter is using its default or an explicitly provided value.
• Documentation
  • Updated the issue status record with reproduction details, validation results, and review progress.

[linear]

B-1061

[vercel]

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Project	Deployment	Actions	Updated (UTC)
beps	Ready	Preview, Comment	Jul 29, 2026 9:24am
promptfiddle	Ready	Preview, Comment	Jul 29, 2026 9:24am
promptfiddle2	Ready	Preview, Comment	Jul 29, 2026 9:24am

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Review skipped

Review was skipped as selected files did not have any reviewable changes.

💤 Files selected but had no reviewable changes (1)

• issue-overview.md

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: b3a40dc8-1100-4df1-8e59-b2090ee9b19a

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Reviewing files that changed from the base of the PR and between cf0470d and 147a0df.

📒 Files selected for processing (1)

• issue-overview.md

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📝 Walkthrough

Walkthrough

ParamRow now displays default expressions as placeholders only for omitted parameters, while explicit values receive an empty placeholder. The issue overview records the B-1061 investigation, implementation, validation, and PR status.

Changes

Argument placeholder update

Layer / File(s)	Summary
Mode-aware placeholder behavior typescript2/pkg-playground/src/ArgsForm.tsx, issue-overview.md	FieldInput receives a default-expression placeholder only when a parameter is omitted, an empty string for explicit values, and undefined when no default exists. The issue status records the root cause, implementation, validation, and PR details.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• BoundaryML/baml#4270: Related ArgsForm.tsx work conditionally displays default expressions for defaulted and omitted parameters.

Poem

A bunny spots a placeholder bright,
Then clears it when values come into sight.
Defaults appear when fields sleep still,
Explicit inputs show their will.
B-1061 hops toward done—
With tested changes, nearly won!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: hiding default placeholders for explicit arguments in the playground form.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/b-1061-default-arg-placeholder

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[sxlijin]

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