fix(plugins): SIGKILL exec children that ignore SIGTERM

- Escalate timed-out or aborted plugin exec children to SIGKILL after a grace period
- Move ai-explain example to assets/plugins and convert it to CommonJS
- Update plugin docs for the new path and the .js/.mjs module formats

assets/plugins/ai-explain/main.js

@@ -0,0 +1,134 @@
+// Sends the current subtitle line, with a few lines of context, to `codex exec` and shows the
+// answer in the SubMiner plugin panel. Registers two actions: `explain` and `translate`.
+const { mkdtemp, readFile, rm } = require('node:fs/promises');
+const os = require('node:os');
+const path = require('node:path');
+
+const DEFAULT_SETTINGS = {
+  codexPath: 'codex',
+  model: '',
+  // Passed as -c model_reasoning_effort; low keeps answers to a few seconds. Empty uses your Codex config.
+  reasoningEffort: 'low',
+  before: 2,
+  after: 1,
+  timeoutMs: 120_000,
+  pause: true,
+  prompts: {},
+};
+
+const ACTIONS = {
+  explain: {
+    title: 'Grammar',
+    prompt:
+      'You are a Japanese tutor. Explain the line marked >>> for an intermediate learner. ' +
+      'Use the other lines only as context. Reply in English markdown: a natural translation, ' +
+      'then a bullet list of the grammar points and notable vocabulary. Be concise.',
+  },
+  translate: {
+    title: 'Translation',
+    prompt:
+      'Translate the line marked >>> into natural English. Use the other lines only as context. ' +
+      'Reply with the translation, then one short note only if the line is ambiguous.',
+  },
+};
+
+function activate(ctx) {
+  const settings = { ...DEFAULT_SETTINGS, ...ctx.settings };
+  for (const [name, action] of Object.entries(ACTIONS)) {
+    const prompt = settings.prompts?.[name] ?? action.prompt;
+    ctx.actions.register(name, () => ask(ctx, settings, action.title, prompt));
+  }
+}
+
+function quote(text) {
+  return text
+    .split('\n')
+    .map((line) => `> ${line}`)
+    .join('\n');
+}
+
+// Subtitles wrap across lines; flatten each cue so the >>> marker covers all of it.
+function oneLine(text) {
+  return text
+    .split('\n')
+    .map((part) => part.trim())
+    .filter(Boolean)
+    .join(' ');
+}
+
+function tail(text, lineCount) {
+  return text.trim().split('\n').slice(-lineCount).join('\n');
+}
+
+async function ask(ctx, settings, title, instructions) {
+  const { before, current, after } = ctx.subtitles.context({
+    before: settings.before,
+    after: settings.after,
+  });
+  if (!current) {
+    ctx.notify('No subtitle line to send.', { variant: 'warning' });
+    return;
+  }
+  if (settings.pause) ctx.mpv.command(['set', 'pause', 'yes']);
+
+  const header = quote(current.text);
+  const panel = ctx.ui.panel({ title, markdown: `${header}\n\n_Asking Codex..._` });
+  const prompt = [
+    instructions,
+    '',
+    'Subtitles:',
+    ...before.map((line) => oneLine(line.text)),
+    `>>> ${oneLine(current.text)}`,
+    ...after.map((line) => oneLine(line.text)),
+  ].join('\n');
+
+  // Codex runs in an empty read-only directory so any command it tries cannot touch real files.
+  const workDir = await mkdtemp(path.join(os.tmpdir(), 'subminer-ai-explain-'));
+  const answerPath = path.join(workDir, 'answer.md');
+  const args = [
+    'exec',
+    '--ephemeral',
+    '--skip-git-repo-check',
+    '--sandbox',
+    'read-only',
+    '--color',
+    'never',
+    '-C',
+    workDir,
+    '-o',
+    answerPath,
+  ];
+  if (settings.model) args.push('-m', settings.model);
+  if (settings.reasoningEffort) {
+    args.push('-c', `model_reasoning_effort=${JSON.stringify(settings.reasoningEffort)}`);
+  }
+  args.push('-');
+
+  try {
+    const result = await ctx.exec(settings.codexPath, args, {
+      stdin: prompt,
+      timeoutMs: settings.timeoutMs,
+      signal: panel.signal,
+    });
+    if (result.exitCode !== 0) {
+      throw new Error(tail(result.stderr, 6) || `codex exited with code ${result.exitCode}`);
+    }
+    const answer = (await readFile(answerPath, 'utf8')).trim();
+    panel.update({ markdown: `${header}\n\n${answer || '_Codex returned an empty answer._'}` });
+  } catch (error) {
+    // Closing the panel aborts the request; there is nobody left to show the error to.
+    if (panel.signal.aborted) return;
+    const message =
+      error?.code === 'ENOENT'
+        ? `Cannot find \`${settings.codexPath}\`. Set \`plugins.ai-explain.settings.codexPath\` to its full path.`
+        : String(error?.message ?? error);
+    ctx.log.warn(`Codex request failed: ${message}`);
+    panel.update({
+      markdown: `${header}\n\n**Codex request failed.**\n\n\`\`\`\n${message}\n\`\`\``,
+    });
+  } finally {
+    await rm(workDir, { recursive: true, force: true });
+  }
+}
+
+module.exports = { activate };