feat(server): in-memory async job store with thread-pool worker

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/jobs.py

@@ -0,0 +1,61 @@
+"""In-memory async job store. Personal-scale: jobs are lost on restart.
+Generic — knows nothing about musicfetch; callers pass a no-arg `fn`."""
+import time
+import uuid
+from concurrent.futures import ThreadPoolExecutor
+from dataclasses import dataclass, field
+from typing import Any, Callable, Optional
+
+_EXECUTOR = ThreadPoolExecutor(max_workers=2)
+JOBS: "dict[str, Job]" = {}
+_MAX_JOBS = 200  # cap to bound memory
+
+
+@dataclass
+class Job:
+    id: str
+    status: str                       # queued | running | done | failed
+    hit: Any
+    message: str
+    result: Optional[dict] = None
+    error: Optional[str] = None
+    created_at: float = field(default_factory=time.time)
+    updated_at: float = field(default_factory=time.time)
+
+
+def _touch(job: "Job", **changes):
+    for k, v in changes.items():
+        setattr(job, k, v)
+    job.updated_at = time.time()
+
+
+def _evict_if_needed():
+    if len(JOBS) <= _MAX_JOBS:
+        return
+    for jid in sorted(JOBS, key=lambda j: JOBS[j].created_at)[: len(JOBS) - _MAX_JOBS]:
+        JOBS.pop(jid, None)
+
+
+def create_job(hit: Any, message: str) -> "Job":
+    job = Job(id=uuid.uuid4().hex[:8], status="queued", hit=hit, message=message)
+    JOBS[job.id] = job
+    _evict_if_needed()
+    return job
+
+
+def get_job(job_id: str) -> Optional["Job"]:
+    return JOBS.get(job_id)
+
+
+def run_job(job_id: str, fn: Callable[[], dict], done_message: str,
+            fail_message: str = "Something went wrong while fetching.") -> None:
+    def _task():
+        job = JOBS[job_id]
+        _touch(job, status="running")
+        try:
+            result = fn()
+            _touch(job, status="done", result=result, message=done_message)
+        except Exception as e:  # noqa: BLE001 — record any failure on the job
+            _touch(job, status="failed", error=f"{type(e).__name__}: {e}",
+                   message=fail_message)
+    _EXECUTOR.submit(_task)