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_override_provisional.py

@@ -0,0 +1,180 @@
+"""IMP-47B u3 — override-selected reject frames are admitted as provisional.
+
+Scope (this slice):
+  Helper `_apply_frame_override_to_unit` (src/phase_z2_pipeline.py) covers
+  the three probe layers used by the `--override-frame` path:
+
+    1. ``v4_candidates`` exact match (non-reject; existing behaviour).
+    2. Full 32 V4 judgments probe (reject inclusive) — when the user
+       picks a reject frame, the unit is promoted to
+       ``provisional=True`` with ``label="reject"`` so Step 12
+       (IMP-47B u4) admits the AI repair path.
+    3. Raw fall-through (template_id only) — no provisional promotion,
+       no label mutation.
+
+Frame visual / contract stay untouched per the AI isolation contract
+(frame auto-swap forbidden — AI re-places content into the existing
+frame only). Sibling test confirms a non-reject override still goes
+through the v4_candidates path without provisional promotion.
+
+Synthetic naming convention mirrors tests/test_phase_z2_imp30_first_render.py
+(MOCK_ prefix mandatory, no real catalog template_id / frame_id leakage).
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Optional
+
+from src.phase_z2_pipeline import _apply_frame_override_to_unit
+
+
+@dataclass
+class _StubCandidate:
+    template_id: str
+    frame_id: str
+    frame_number: int
+    confidence: float
+    label: str
+
+
+@dataclass
+class _StubUnit:
+    source_section_ids: list[str]
+    frame_template_id: Optional[str] = None
+    frame_id: Optional[str] = None
+    frame_number: int = 0
+    confidence: float = 0.0
+    label: Optional[str] = None
+    provisional: bool = False
+    v4_candidates: list = field(default_factory=list)
+
+
+def _v4_with_reject(section_id: str, target_tid: str) -> dict:
+    """Synthetic V4 dict with target_tid mapped to a reject judgment.
+
+    Mirrors the production V4 schema surface (``mdx_sections`` →
+    ``judgments_full32`` → list of judgment dicts with template_id /
+    frame_id / frame_number / confidence / label). Two judgments so we
+    can also assert that the helper picks the reject entry rather than
+    the first non-reject one when the template_ids differ.
+    """
+    return {
+        "mdx_sections": {
+            section_id: {
+                "judgments_full32": [
+                    {
+                        "template_id": "MOCK_T_other",
+                        "frame_id": "F_other",
+                        "frame_number": 1,
+                        "confidence": 0.85,
+                        "label": "use_as_is",
+                    },
+                    {
+                        "template_id": target_tid,
+                        "frame_id": "F_reject",
+                        "frame_number": 32,
+                        "confidence": 0.40,
+                        "label": "reject",
+                    },
+                ],
+            },
+        },
+    }
+
+
+# ─── Case 1 : reject override → provisional promotion ────────────
+
+
+def test_override_to_reject_judgment_marks_unit_provisional():
+    """User picks a reject frame → unit.label=reject, provisional=True.
+
+    Frame metadata is sourced from the reject judgment (frame_id /
+    frame_number / confidence) so Step 9 metadata stays consistent.
+    """
+    unit = _StubUnit(
+        source_section_ids=["MOCK_S1"],
+        frame_template_id="MOCK_T_auto",
+        frame_id="F_auto",
+        frame_number=5,
+        confidence=0.90,
+        label="use_as_is",
+        provisional=False,
+    )
+    v4 = _v4_with_reject("MOCK_S1", "MOCK_T_reject")
+
+    meta = _apply_frame_override_to_unit(unit, "MOCK_T_reject", v4)
+
+    assert meta == "v4_reject_judgment_provisional"
+    assert unit.frame_template_id == "MOCK_T_reject"
+    assert unit.frame_id == "F_reject"
+    assert unit.frame_number == 32
+    assert unit.confidence == 0.40
+    assert unit.label == "reject"
+    assert unit.provisional is True
+
+
+# ─── Case 2 : non-reject override → existing v4_candidates path ───
+
+
+def test_override_to_v4_candidate_keeps_non_provisional():
+    """User picks a non-reject candidate → existing v4_candidates path.
+
+    Helper takes the early v4_candidates branch without consulting the
+    full 32 judgments. provisional remains False (normal-path AI=0
+    contract — IMP-30 / IMP-47B router gate intact for this unit).
+    """
+    unit = _StubUnit(
+        source_section_ids=["MOCK_S2"],
+        frame_template_id="MOCK_T_auto",
+        frame_id="F_auto",
+        frame_number=3,
+        confidence=0.95,
+        label="use_as_is",
+        provisional=False,
+        v4_candidates=[
+            _StubCandidate(
+                template_id="MOCK_T_pick",
+                frame_id="F_pick",
+                frame_number=2,
+                confidence=0.85,
+                label="light_edit",
+            ),
+        ],
+    )
+    v4 = {"mdx_sections": {}}  # full-judgment probe must NOT be reached
+
+    meta = _apply_frame_override_to_unit(unit, "MOCK_T_pick", v4)
+
+    assert meta == "v4_candidates"
+    assert unit.frame_template_id == "MOCK_T_pick"
+    assert unit.frame_id == "F_pick"
+    assert unit.label == "light_edit"
+    assert unit.provisional is False
+
+
+# ─── Case 3 : unknown template → raw fall-through (no provisional) ─
+
+
+def test_override_unknown_template_falls_through_without_provisional():
+    """Template ID absent from v4_candidates AND from judgments_full32 →
+    raw_template_id_only path. No provisional flag, no label change.
+    """
+    unit = _StubUnit(
+        source_section_ids=["MOCK_S3"],
+        frame_template_id="MOCK_T_auto",
+        frame_id="F_auto",
+        frame_number=4,
+        confidence=0.92,
+        label="use_as_is",
+        provisional=False,
+    )
+    v4 = {"mdx_sections": {}}
+
+    meta = _apply_frame_override_to_unit(unit, "MOCK_T_unknown", v4)
+
+    assert meta == "raw_template_id_only"
+    assert unit.frame_template_id == "MOCK_T_unknown"
+    # frame_id / label unchanged — caller's print path warns on this case.
+    assert unit.frame_id == "F_auto"
+    assert unit.label == "use_as_is"
+    assert unit.provisional is False