feat(#76): IMP-47B reject-as-AI-adaptation activation (u1~u13 backend + tests)

- u1~u9: AI fallback infrastructure (router/prompts/schema/validator) + Step 12 hook
- u10: e2e reject chain (writes final.html with AI-repaired slot, full coverage)
- u11: frontend wiring deferred to follow-up commit (split from IMP-41 hunks)
- u12: coverage_invariant guard
- u13: cache save gate (visual_check PASS + user_approved/auto_cache) — Codex #22 verified

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_imp47b_step12_ai_wiring.py

@@ -0,0 +1,154 @@
+"""IMP-47B u4 + u6 — Step 12 AI repair wiring + audit artifact tests.
+
+Scope (this slice):
+  * u4 — Helper ``_run_step12_ai_repair`` (src/phase_z2_pipeline.py)
+    wires the pipeline's local route-hint helper (``_imp05_route_hint``),
+    the frame contract loader (``get_contract``), and a
+    templates/phase_z2/families partial reader
+    (``_load_frame_partial_html``) into
+    ``gather_step12_ai_repair_proposals``.
+  * u6 — The gather records flow into ``_write_step_artifact`` under
+    ``step12_ai_repair.json``. The audit shape must stay
+    JSON-serialisable (no Pydantic / dataclass leakage) so the artifact
+    write never raises on real runs.
+
+The router short-circuits when ``settings.ai_fallback_enabled`` is
+False (default), so AI=0 for non-AI-route units stays a structural
+guarantee. Synthetic naming mirrors tests/test_imp47b_override_provisional.py
+(MOCK_ prefix; no real catalog template_id / frame_id leakage).
+
+u5 (PARTIAL_OVERRIDES apply), u7 (coverage invariant), and u8
+(slide_status surfacing) are out of scope for this unit.
+"""
+from __future__ import annotations
+
+import json
+from dataclasses import dataclass, field
+
+from src.phase_z2_pipeline import (
+    _load_frame_partial_html,
+    _run_step12_ai_repair,
+    _write_step_artifact,
+)
+
+
+@dataclass
+class _StubUnit:
+    label: str | None
+    provisional: bool
+    frame_template_id: str = "MOCK_T_x"
+    frame_id: str = "MOCK_F_x"
+    source_section_ids: list[str] = field(default_factory=lambda: ["MOCK_S1"])
+    raw_content: str = "MOCK_raw"
+    v4_rank: int | None = 1
+    cardinality: int | None = None
+    layout_preset: str = ""
+    zone_position: str = ""
+    source_shape: str = "paragraph"
+    h3_count: int = 0
+    char_count: int = 0
+
+
+# ─── Case 1 : mixed units → per-unit skip_reason classification ─────
+
+
+def test_mixed_units_classified_by_route_and_provisional_flag():
+    """Reject + restructure provisional both route to ai_adaptation;
+    use_as_is / light_edit / non-provisional skip without router call.
+
+    With ai_fallback_enabled=False (default) the router returns None,
+    so the two ai_adaptation provisional units record
+    ``skip_reason='router_short_circuit'``; the rest record their
+    structural skip_reason (not_provisional / route_not_ai_adaptation).
+    """
+    units = [
+        _StubUnit(label="use_as_is", provisional=False),
+        _StubUnit(label="light_edit", provisional=True),
+        _StubUnit(label="restructure", provisional=True),
+        _StubUnit(label="reject", provisional=True),
+        _StubUnit(label="restructure", provisional=False),
+    ]
+    records = _run_step12_ai_repair(units)
+    assert [r["skip_reason"] for r in records] == [
+        "not_provisional",
+        "route_not_ai_adaptation:deterministic_minor_adjustment",
+        "router_short_circuit",
+        "router_short_circuit",
+        "not_provisional",
+    ]
+    assert [r["route_hint"] for r in records] == [
+        "direct_render",
+        "deterministic_minor_adjustment",
+        "ai_adaptation_required",
+        "ai_adaptation_required",
+        "ai_adaptation_required",
+    ]
+    assert all(r["ai_called"] is False for r in records)
+
+
+# ─── Case 2 : reject provisional unit reaches AI gate ───────────────
+
+
+def test_reject_provisional_unit_reaches_router_short_circuit():
+    """Reject + provisional → route_hint=ai_adaptation_required.
+
+    Router short-circuit (flag-off default) is the only thing keeping
+    AI from firing; the wiring proves reject is no longer blocked by
+    Step 12's bespoke design_reference_only skip (removed by u2).
+    """
+    records = _run_step12_ai_repair([_StubUnit(label="reject", provisional=True)])
+    assert records[0]["route_hint"] == "ai_adaptation_required"
+    assert records[0]["skip_reason"] == "router_short_circuit"
+    assert records[0]["ai_called"] is False
+    # cache_key / fingerprints populated only after the route + provisional
+    # gates pass — confirms gather reached the AI-eligible code path.
+    assert records[0]["cache_key"] is not None
+    assert records[0]["fingerprints"] is not None
+
+
+# ─── Case 3 : frame visual loader degrades on missing partial ──────
+
+
+def test_load_frame_partial_html_returns_empty_for_missing_file():
+    """__empty__ shell (IMP-30) and any unknown template_id → "".
+
+    Keeps gather() crash-free for the IMP-30 first-render-invariant
+    path where the synthesized empty-shell unit has no families partial.
+    """
+    assert _load_frame_partial_html("__empty__") == ""
+    assert _load_frame_partial_html("MOCK_T_does_not_exist") == ""
+
+
+# ─── Case 4 (u6) : audit artifact write is JSON-serialisable ────────
+
+
+def test_step12_ai_repair_artifact_writes_json_serialisable_records(tmp_path):
+    """IMP-47B u6 — gather records feed ``_write_step_artifact`` as the
+    ``step12_ai_repair.json`` audit. Confirms the gather schema contains
+    only JSON-native primitives (str / int / None / bool / list / dict)
+    so the artifact write never raises on real runs and the audit
+    payload preserves per-unit ``route_hint`` / ``skip_reason`` /
+    ``ai_called`` for reviewers.
+    """
+    records = _run_step12_ai_repair([
+        _StubUnit(label="reject", provisional=True),
+        _StubUnit(label="use_as_is", provisional=False),
+    ])
+    fpath = _write_step_artifact(
+        tmp_path, 12, "ai_repair",
+        data={"per_unit": records},
+        outputs=["step12_ai_repair.json"],
+    )
+    assert fpath.is_file()
+    assert fpath.name == "step12_ai_repair.json"
+    payload = json.loads(fpath.read_text(encoding="utf-8"))
+    assert payload["step_num"] == 12
+    assert payload["step_name"] == "ai_repair"
+    assert payload["step_status"] == "done"
+    per_unit = payload["data"]["per_unit"]
+    assert len(per_unit) == 2
+    assert per_unit[0]["route_hint"] == "ai_adaptation_required"
+    assert per_unit[0]["skip_reason"] == "router_short_circuit"
+    assert per_unit[0]["ai_called"] is False
+    assert per_unit[1]["route_hint"] == "direct_render"
+    assert per_unit[1]["skip_reason"] == "not_provisional"