Improve slow-start prompt behavior

[gtsiolis]

Motivation

When LocalStack takes longer than the interactive startup timeout, the recovery prompt wraps awkwardly and hides its shortcut keys. More importantly, startup health checks pause while the prompt is open, so it can remain stuck after the emulator is ready and a stale Stop selection can stop a healthy emulator.

Solution

• Render the slow-start actions as vertical, shortcut-first choices.
• Continue monitoring readiness and container exit while the prompt is visible.
• Dismiss only the matching prompt when startup resolves automatically.
• Recheck readiness before stopping to protect an emulator that became healthy during the prompt.
• Add regression tests for layout, automatic dismissal, and readiness/Stop races.

BEFORE / AFTER

Aspect	Before	After
Prompt layout	Question and actions form one long line and wrap awkwardly	Question and actions render on separate lines
Shortcuts	Keep waiting [W] / Stop LocalStack and exit [S]	[W] Keep waiting / [S] Stop and exit
Successful startup	Prompt remains stuck until a key is pressed	Prompt closes automatically and the success sequence appears
Stop action	A stale prompt can stop an emulator that has become ready	Readiness is checked again before stopping
Monitoring	Health checks pause while awaiting input	Health and exit monitoring continue behind the prompt

BEFORE	AFTER

Docs

Docs assessment

No documentation changes are needed. This refines existing interactive startup behavior and keeps the recovery command visible in the prompt.

Review

Self-merge candidate: this is a small, already-discussed UX fix with focused unit and race regression coverage.

Validation

• go test -race ./internal/container -run 'TestStartupMonitorAwait_(InteractivePromptKeepWaitingThenStop|DismissesPromptWhenEmulatorBecomesReady|DoesNotStopEmulatorThatBecameReadyBeforeSelection)$' -count=1
• go test ./internal/ui/... ./internal/output/... -count=1
• make build
• git diff --check

Closes DEVX-1051

Co-Authored-By: Claude noreply@anthropic.com

[gtsiolis]

@tiurin could you take a look since you added this in #449. Friendly reminder to also ask for a peer review when there are many moving parts on the interactive or non-interactive outputs. Cc @localstack/devx

[skyrpex]

Looks much better now, thanks!

[tiurin]

@tiurin could you take a look since you added this in #449. Friendly reminder to also ask for a peer review when there are many moving parts on the interactive or non-interactive outputs. Cc @localstack/devx

thanks @gtsiolis, great catch on not stopping the emulator that eventually started while the prompt was on-screen. 👏 Also, looks much better with line split. 👍

Just to confirm, #449 is related to a different problem. Did you mean #390? That one was peer-reviewed. But definitely agree that we can use more of cross-testing ourselves and validate the user experience more often by trying out a binary from the branch while reviewing. 💯 Could be a good default reviewing behaviour we can add to contributing guidelines, wdyt?

[tiurin]

However, options added in #449 don't have vertical rendering applied, will follow-up on it -> #458

[gtsiolis]

@tiurin Correct! Thanks for the follow up!

A design rule to follow for when to use what, is ...

• Inline Y/n for binary confirmations: “Remove snapshot? [y/N]”
• Vertical choices for distinct actions: “Keep waiting”, “Stop and exit”, etc.

Cc @localstack/devx for visibility.

[gtsiolis]

Thanks for merging, @tiurin, and for reviewing, @skyrpex! 🏀

---

Generated by Claude Code

[tiurin]

@tiurin Correct! Thanks for the follow up!

A design rule to follow for when to use what, is ...

• Inline Y/n for binary confirmations: “Remove snapshot? [y/N]”
• Vertical choices for distinct actions: “Keep waiting”, “Stop and exit”, etc.

Cc @localstack/devx for visibility.

Nice! I think we can make the code speak this design rule. This will guide developer towards choosing the right intent and hide rendering details like vertical behind it. I've generated a quick draft PR: #459. It's work in progress but curious what do you think about the intent @gtsiolis @localstack/devx?