refactor(codex-imagegen): extract backend to packages/baoyu-codex-imagegen workspace

Move the codex-imagegen wrapper out of scripts/ into its own workspace
package alongside baoyu-md, baoyu-chrome-cdp, and baoyu-fetch. Drop the
bash shim — src/main.ts now carries a `#\!/usr/bin/env bun` shebang and
serves as the sole entrypoint. Add scripts/sync-codex-imagegen.sh so
skills/baoyu-image-gen/scripts/codex-imagegen/ can be regenerated from
packages/baoyu-codex-imagegen/src/ for skill self-containment. Update
CLAUDE.md, docs/codex-imagegen-backend.md, and the CI workflow paths
accordingly.

packages/baoyu-codex-imagegen/src/parser.test.ts

@@ -0,0 +1,49 @@
+import { test, expect } from "bun:test";
+import { parseEventStream, hasImageGenInvocation } from "./parser.ts";
+
+const REAL_PoC_STREAM = `{"type":"thread.started","thread_id":"019e40d3-30e3-7030-874d-773bc0d6d1eb"}
+{"type":"turn.started"}
+{"type":"item.started","item":{"id":"item_0","type":"command_execution","command":"sed -n '1,5p' /tmp/x.md","status":"in_progress"}}
+{"type":"item.completed","item":{"id":"item_0","type":"command_execution","command":"sed -n '1,5p' /tmp/x.md","exit_code":0,"status":"completed"}}
+{"type":"item.started","item":{"id":"item_1","type":"command_execution","command":"cp /Users/x/.codex/generated_images/019e40d3/ig_abc.png /tmp/out.png","status":"in_progress"}}
+{"type":"item.completed","item":{"id":"item_1","type":"command_execution","command":"cp /Users/x/.codex/generated_images/019e40d3/ig_abc.png /tmp/out.png","exit_code":0,"status":"completed"}}
+{"type":"item.completed","item":{"id":"item_2","type":"agent_message","text":"{\\"status\\":\\"ok\\",\\"path\\":\\"/tmp/out.png\\",\\"bytes\\":1234567}"}}
+{"type":"turn.completed","usage":{"input_tokens":100000,"cached_input_tokens":80000,"output_tokens":500,"reasoning_output_tokens":50}}`;
+
+test("parseEventStream extracts threadId, toolCalls, agentMessage, usage", () => {
+  const r = parseEventStream(REAL_PoC_STREAM);
+  expect(r.threadId).toBe("019e40d3-30e3-7030-874d-773bc0d6d1eb");
+  expect(r.toolCalls.length).toBe(3);
+  expect(r.usage).toEqual({
+    input: 100000,
+    cached_input: 80000,
+    output: 500,
+    reasoning: 50,
+  });
+  expect(r.agentMessage).toContain('"status":"ok"');
+});
+
+test("parseEventStream tolerates malformed lines", () => {
+  const stream = `not json at all
+{"type":"thread.started","thread_id":"abc"}
+{partial json
+{"type":"turn.completed","usage":{"input_tokens":1,"cached_input_tokens":0,"output_tokens":1,"reasoning_output_tokens":0}}`;
+  const r = parseEventStream(stream);
+  expect(r.threadId).toBe("abc");
+  expect(r.usage?.input).toBe(1);
+});
+
+test("hasImageGenInvocation finds shell calls touching generated_images", () => {
+  const r = parseEventStream(REAL_PoC_STREAM);
+  // image_gen itself is not an event; inferred via generated_images cp path
+  // this test only verifies parser behavior; driver logic lives in validator
+  const hasCp = r.toolCalls.some((tc) => tc.command?.includes("generated_images"));
+  expect(hasCp).toBe(true);
+});
+
+test("hasImageGenInvocation (proper) returns false when no image_gen tool", () => {
+  expect(hasImageGenInvocation([{ id: "1", tool: "shell", status: "completed" }])).toBe(false);
+  expect(
+    hasImageGenInvocation([{ id: "1", tool: "image_gen", status: "completed" }]),
+  ).toBe(true);
+});