fix(coding-agent): remove spacing artifacts for suppressed custom tool renders

[alasano]

Summary

This PR fixes interactive transcript spacing when custom tool renderers intentionally suppress per-call output.

Use case: extensions that group contiguous tool calls into a single UI block (for example grouped file reads) should be able to hide individual tool entries without leaving empty rows or extra spacing.

Related to #1715 (approval issue, now closed).

Changes

• Allow custom tool renderers to explicitly render nothing:
  • renderCall?: (...) => Component | undefined
  • renderResult?: (...) => Component | undefined
• Remove the injected blank spacer before streaming tool blocks in interactive mode.
• Update ToolExecutionComponent so suppressed custom tool output can render as true zero-height (no leftover transcript footprint).
• Update HTML custom tool renderer handling to safely fall back when custom renderers return undefined.
• Add tests for:
  • suppressed custom renderer output (renders nothing)
  • built-in tool rendering remains visible
  • custom renderer output remains visible when a component is returned

Scope

This is an intentionally minimal, non-breaking fix for extension-driven grouped tool UIs.
A fuller transcript-level grouping/coalescing API can be done separately.

Validation

• npm run check
• ./test.sh

[badlogic]

Cheers!

[alasano]

Cheers!

@badlogic my pleasure! thanks for merging this :)

here's what it enabled me to do as an extension now FYI

prior to this fix it was appending 5 empty new lines below the component (one per file read) which made the UI much worse.