chroma_cache_path — v1

Why this iteration: Lifted verbatim from conductor/code_styleguides/chroma_cache.md §"The Rule" + §"The Pre-Cleanup Pattern" (lines 5-50). This is the baseline encoding — the rule-plus-rationale-plus-anti-patterns style currently in production. Future variants will test alternative encodings (rule-only, before/after) against this baseline.

Source: conductor/code_styleguides/chroma_cache.md:5-50

Chroma Cache Path Styleguide

The Rule

The ChromaDB persistent vector cache lives at:

<project_root>/tests/artifacts/.slop_cache/chroma_<collection_name>/

NOT at the per-run tests/artifacts/live_gui_workspace_<timestamp>/ subdir.

Tests that interact with RAG MUST pre-clean the cache to avoid persistent state from prior tests in the batched run.

Why This Rule Exists

The chroma cache path is auto-derived from RAGEngine._init_vector_store() (src/rag_engine.py:108-125):

db_path = os.path.abspath(os.path.join(
    self.base_dir, ".slop_cache", f"chroma_{vs_config.collection_name}"
))

self.base_dir is computed as Path(active_project_path).parent. The trailing-slash bug: when the test config produces a project path ending in / (e.g., from os.path.join with a trailing /), Path(p).parent returns the directory ONE LEVEL HIGHER than expected. So the chroma cache lands at tests/artifacts/.slop_cache/ (the parent of the per-run live_gui_workspace_<timestamp>/ subdir) instead of inside the per-run subdir.

The Pre-Cleanup Pattern

RAG tests should wipe the chroma cache BEFORE pushing RAG config. The pattern is in tests/test_rag_phase4_final_verify.py:

from pathlib import Path
import shutil

def test_phase4_final_verify(live_gui):
    # Wipe any stale chroma from prior batched runs
    cache = Path("tests/artifacts/.slop_cache/chroma_test_final_verify")
    if cache.exists():
        shutil.rmtree(cache, ignore_errors=True)
    # ... rest of test

ignore_errors=True is required because:

On Windows, the chroma client may still hold file handles; rmtree may fail with WinError 32 (sharing violation).
If a parallel xdist worker is mid-write, the rmtree can race; ignore_errors lets the next worker's write retry.

Anti-Patterns

❌ Assuming the cache is per-run:

def test_rag(live_gui, live_gui_workspace):
    # WRONG: live_gui_workspace is a per-run subdir, but the chroma
    # cache is at tests/artifacts/.slop_cache/, NOT under live_gui_workspace
    cache = live_gui_workspace / ".slop_cache" / "chroma_test"
    if cache.exists():
        shutil.rmtree(cache)  # Doesn't find the actual cache

❌ Not pre-cleaning at all:

def test_rag(live_gui):
    # WRONG: no pre-cleanup. If a prior batched run with a different

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