feat(harness): P4 — custom-test ergonomics (rcust)

Placement RULE: discovery.custom_tests covers ONLY functional/ + playwright/ —
the top-level test_*.py glob for recipe dirs is removed (top level is reserved
for lifecycle overlays; zero in-repo users of top-level custom tests, verified
by sweep). Lifecycle-name exclusion inside the subdirs stays as the double-run
safety net. HC2 default-deny unchanged (repo-local custom now pinned via
functional/ in the gate test).

New conftest fixture op_state: parses $CCCI_OP_STATE_FILE (op context: versions,
artifact paths), skipping with a clear reason when unset/absent/unparseable —
overlay tests read op facts from the fixture instead of hand-parsing env (zero
existing hand-parsers found; the fixture is the documented path forward). deps
fixture landed in P2d.

Unit tests: placement-rule discovery tests (top-level custom NOT discovered;
functional/playwright are; misfiled lifecycle names excluded), op_state fixture
contract (reads file / skips without env / skips on missing file), deps fixture
attribute sugar.

Verified on cc-ci: cc-ci-run -m pytest tests/unit -q -> 184 passed; scripts/lint.sh -> PASS.

runner/harness/discovery.py

@@ -11,7 +11,8 @@ hook; the orchestrator decides additive-vs-skip. Sources, in precedence order
       > cc-ci       tests/<recipe>/test_<op>.py
     (the generic tests/_generic/test_<op>.py is the always-present floor, run separately by default)
 
-    custom (non-lifecycle) test_*.py — ALL run, additively, from BOTH locations (opt-in).
+    custom test_*.py (functional/ + playwright/ ONLY, rcust P4 placement rule) — ALL run,
+        additively, from BOTH locations (opt-in).
 
     install-steps hook — install_steps.sh: repo-local > cc-ci, or none.
 
@@ -100,29 +101,22 @@ def resolve_op(recipe: str, op: str, repo_local_dir: str | None) -> tuple[str, s
 
 
 def custom_tests(recipe: str, repo_local_dir: str | None) -> list[tuple[str, str]]:
-    """All non-lifecycle test_*.py from cc-ci's tests/<recipe>/ and (if approved) the recipe's
-    repo-local tests/. Discovered locations (Phase 2 §4.1):
-      - the top-level dir   tests/<recipe>/test_*.py  (legacy + cross-cutting)
-      - functional/         tests/<recipe>/functional/test_*.py  (parity ports + recipe-specific)
-      - playwright/         tests/<recipe>/playwright/test_*.py  (UI flows P6)
-    Files named `test_<op>.py` (lifecycle ops) are excluded from this list — the orchestrator runs
-    those in their lifecycle tier, not the custom one. Repo-local is consulted only for
-    allowlist-approved recipes (HC2)."""
+    """All custom-tier test_*.py from cc-ci's tests/<recipe>/ and (if approved) the recipe's
+    repo-local tests/. PLACEMENT RULE (rcust P4): custom tests live ONLY under
+      - functional/   tests/<recipe>/functional/test_*.py  (parity ports + recipe-specific)
+      - playwright/   tests/<recipe>/playwright/test_*.py  (UI flows)
+    A top-level test_*.py is a LIFECYCLE OVERLAY (test_<op>.py) and nothing else — top-level
+    non-lifecycle files are NOT discovered (zero users at the time of the change; the lifecycle-
+    name exclusion below stays as a safety net so a misfiled test_<op>.py can never double-run).
+    Repo-local is consulted only for allowlist-approved recipes (HC2)."""
     lifecycle_names = {f"test_{op}.py" for op in LIFECYCLE_OPS}
     subdirs = ("functional", "playwright")
     found: list[tuple[str, str]] = []
     for source, d in (("cc-ci", cc_ci_dir(recipe)), ("repo-local", _gated(recipe, repo_local_dir))):
         if not d or not os.path.isdir(d):
             continue
-        # top-level (legacy / cross-cutting tests not under functional/playwright)
-        for p in sorted(glob.glob(os.path.join(d, "test_*.py"))):
-            if os.path.basename(p) not in lifecycle_names:
-                found.append((source, p))
-        # functional/ and playwright/ subdirs (Phase 2 §4.1)
         for sub in subdirs:
             for p in sorted(glob.glob(os.path.join(d, sub, "test_*.py"))):
-                # Phase-2 layout: lifecycle ops never live under functional/playwright, but be
-                # explicit so a misfiled file doesn't silently get double-run.
                 if os.path.basename(p) not in lifecycle_names:
                     found.append((source, p))
     return found