test(backend): add E2E harness foundation (entrypoints, middleware, LLM/embedding fakes)

surfsense_backend/tests/e2e/fakes/embeddings.py

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+"""Deterministic embedding fakes for E2E.
+
+Mirrors the existing `patched_embed_texts` fixture in
+`surfsense_backend/tests/integration/conftest.py`:
+
+    MagicMock(side_effect=lambda texts: [[0.1] * _EMBEDDING_DIM for _ in texts])
+
+The dimension matches whatever `config.embedding_model_instance.dimension`
+returns in the running process so the fakes are vector-compatible with
+the documents.embedding pgvector column.
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Any
+
+import numpy as np
+
+from app.config import config
+
+logger = logging.getLogger(__name__)
+
+
+def _embedding_dim() -> int:
+    """Resolve the dimension once, lazily, so tests work for any embedding model."""
+    return int(config.embedding_model_instance.dimension)
+
+
+def fake_embed_text(text: str) -> np.ndarray:
+    """Deterministic single-text embedding."""
+    return np.full(shape=(_embedding_dim(),), fill_value=0.1, dtype=np.float32)
+
+
+def fake_embed_texts(texts: list[str]) -> list[np.ndarray]:
+    """Deterministic batch embedding. One vector per input text."""
+    if not texts:
+        return []
+    dim = _embedding_dim()
+    return [
+        np.full(shape=(dim,), fill_value=0.1, dtype=np.float32) for _ in texts
+    ]
+
+
+def install(patches: list[Any]) -> None:
+    """Install embedding patches at every binding site we know about.
+
+    Caller passes a `patches` list that the entrypoint will track in
+    order to start them (and, in principle, stop them on shutdown — we
+    intentionally never stop because the process exits when the test
+    server stops).
+    """
+    from unittest.mock import patch as _patch
+
+    targets = [
+        # Source binding (where the real implementation lives)
+        ("app.utils.document_converters.embed_text", fake_embed_text),
+        ("app.utils.document_converters.embed_texts", fake_embed_texts),
+        # Consumers that did `from app.utils.document_converters import embed_text/texts`
+        ("app.indexing_pipeline.document_embedder.embed_text", fake_embed_text),
+        ("app.indexing_pipeline.document_embedder.embed_texts", fake_embed_texts),
+        # Pipeline service binding (the actual call site for indexing.index)
+        ("app.indexing_pipeline.indexing_pipeline_service.embed_texts", fake_embed_texts),
+    ]
+    for target, replacement in targets:
+        try:
+            p = _patch(target, replacement)
+            p.start()
+            patches.append(p)
+            logger.info("[fake-embeddings] patched %s", target)
+        except (ModuleNotFoundError, AttributeError) as exc:
+            # If a future refactor moves a binding, fail loudly — silent
+            # passthrough to a real embedding model would be expensive
+            # and non-deterministic.
+            raise RuntimeError(
+                f"Could not patch embedding binding {target!r}: {exc!s}. "
+                f"Update surfsense_backend/tests/e2e/fakes/embeddings.py "
+                f"to point at the new binding site."
+            ) from exc