feat: add PR walkthrough generation workflow (#2933)

.github/scripts/opencode-pr-walkthrough-tool.ts

@@ -0,0 +1,38 @@
+import { tool } from "@opencode-ai/plugin"
+import path from "path"
+
+export default tool({
+  description:
+    "Validate and render a complete PR walkthrough JSON object. Retry with corrected JSON when this tool reports a renderer error.",
+  args: {
+    walkthrough: tool.schema
+      .string()
+      .max(2_000_000)
+      .describe("The complete PR walkthrough JSON object as a string"),
+  },
+  async execute(args, context) {
+    const helper = path.join(context.worktree, ".opencode-walkthrough", "render")
+    const sourceEnv = globalThis.process.env
+    const childEnv = Object.fromEntries(
+      ["PATH", "PR_NUMBER", "PR_TITLE", "PR_URL", "PR_REPO", "PR_BASE", "PR_HEAD"]
+        .filter((name) => sourceEnv[name] !== undefined)
+        .map((name) => [name, sourceEnv[name] as string]),
+    )
+    const child = Bun.spawn(["python3", helper], {
+      cwd: context.worktree,
+      env: childEnv,
+      stdin: new Blob([args.walkthrough]),
+      stdout: "pipe",
+      stderr: "pipe",
+    })
+    const [status, stdout, stderr] = await Promise.all([
+      child.exited,
+      new Response(child.stdout).text(),
+      new Response(child.stderr).text(),
+    ])
+    if (status !== 0) {
+      return `Renderer rejected the walkthrough. Correct the JSON and call this tool again.\n${stderr || stdout}`
+    }
+    return stdout.trim()
+  },
+})