fix: ChromaDB unreachable blocks app startup for 30-60s (#326) (#476)

* fix: fail fast when ChromaDB is unreachable instead of blocking startup

* fix: only cache the ChromaDB client after a successful heartbeat

* test: cover ChromaDB fast-fail preflight and no-cache-on-failure

tests/test_chroma_client.py

@@ -0,0 +1,52 @@
+"""Regression tests for the ChromaDB singleton client (issue #326).
+
+Covers the fast-fail preflight (so an unreachable ChromaDB doesn't block
+startup for the full OS connection timeout) and the rule that a failed
+connection must not poison the cached singleton.
+"""
+import socket
+import time
+
+import pytest
+
+import src.chroma_client as cc
+
+
+def _free_port() -> int:
+    """Bind to port 0, grab the assigned port, release it — nothing listens."""
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.bind(("127.0.0.1", 0))
+    port = s.getsockname()[1]
+    s.close()
+    return port
+
+
+def test_port_open_false_for_closed_port_and_is_fast():
+    port = _free_port()
+    t0 = time.monotonic()
+    assert cc._port_open("127.0.0.1", port, timeout=1.0) is False
+    # The whole point: we fail fast, nowhere near the 30-60s OS timeout.
+    assert time.monotonic() - t0 < 5.0
+
+
+def test_port_open_true_for_listening_socket():
+    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    srv.bind(("127.0.0.1", 0))
+    srv.listen(1)
+    host, port = srv.getsockname()
+    try:
+        assert cc._port_open(host, port, timeout=1.0) is True
+    finally:
+        srv.close()
+
+
+def test_get_chroma_client_does_not_cache_when_unreachable(monkeypatch):
+    pytest.importorskip("chromadb")
+    cc.reset_client()
+    monkeypatch.setenv("CHROMADB_HOST", "127.0.0.1")
+    monkeypatch.setenv("CHROMADB_PORT", str(_free_port()))
+    with pytest.raises(RuntimeError):
+        cc.get_chroma_client()
+    # A failed connection must leave the singleton unset so a later call
+    # (once ChromaDB is up) can succeed.
+    assert cc._client is None