feat: add abort execution button to playground

[tomi]

Summary

• The "Run" button transforms into a red "Abort" button while a command is executing
• Clicking Abort or pressing Ctrl+C now calls DELETE /sandboxes/{id}/executions/{exec_id} to kill the server-side process, instead of only aborting the HTTP fetch stream
• Tracks the exec_id from the started event so the correct execution can be targeted for cancellation

Kapture.2026-05-08.at.16.52.38.mp4

Test plan

• Run a long-running command (e.g. sleep 60) and verify the button changes to red "Abort"
• Click Abort and verify the process is killed server-side (exit event shows killed: true)
• Press Ctrl+C during execution and verify the same abort behavior
• Verify the button reverts to "Run" after execution completes or is aborted
• Verify normal command execution still works end-to-end

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="playground/src/app.js">

<violation number="1" location="playground/src/app.js:260">
P1: Abort can miss server-side kill when pressed before `started` arrives, because DELETE is skipped if `currentExecId` is still null.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review, or fix all with cubic.}

[cubic-dev-ai]

P1: Abort can miss server-side kill when pressed before started arrives, because DELETE is skipped if currentExecId is still null.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At playground/src/app.js, line 260:

<comment>Abort can miss server-side kill when pressed before `started` arrives, because DELETE is skipped if `currentExecId` is still null.</comment>

<file context>
@@ -247,19 +248,58 @@ async function execInSandbox(sandboxId, command, timeoutMs = 300000, signal) {
+  currentAbortController.abort();
+  appendOutput('^C', 'error');
+
+  if (execId && sandboxId) {
+    const baseUrl = baseUrlInput.value.trim().replace(/\/+$/, '');
+    try {
</file context>