feat(#39): IMP-30 first-render invariant + abort bypass (2 paths)

Restore first-render invariant: final.html + Step 20 slide_status MUST be
written for every input where Step 0~5 succeed. Two abort paths replaced
with provisional/empty-shell synthesis; MDX content preserved, AI-free.

- u1 V4Match.provisional + lookup_v4_match_with_fallback(allow_provisional)
  chain_exhausted -> synthesize rank-1 provisional (opt-in, default-off)
- u2 CompositionUnit.provisional propagation (single / parent_merged /
  parent_merged_inferred constructors)
- u3 select_composition_units(allow_provisional_fill=True) last-resort
  fill + _candidate_state="selected_provisional"
- u4 pipeline.py path-(a) abort guard replaced with provisional retry +
  terminal __empty__ shell (no sys.exit(1))
- u5 zones_data.provisional -> slide_base.html zone--provisional class +
  data-provisional + needs-adaptation badge (template-only)
- u6 compute_slide_status additive provisional_first_render_count/_units
  (overall enum unchanged per IMP-05 Codex #10 D4)
- u7 regression: tests/test_phase_z2_imp30_first_render.py (28 tests) +
  tests/test_phase_z2_v4_fallback.py (+5 cases)

Guardrails verified: MVP1_ALLOWED_STATUSES unchanged, no calculate_fit,
no LLM in fallback path, no MDX 03/04/05 hardcoding.

Anchor sync (Rule 13): tests/orchestrator_unit/test_imp17_comment_anchor.py
re-pinned 564/565 -> 570/571 to track V4Match.provisional shift at
src/phase_z2_pipeline.py:179-184.

Cross-ref: IMP-05 (#5) §5 defer + Codex #2 first-render invariant.

src/phase_z2_composition.py

@@ -368,6 +368,15 @@ class CompositionUnit:
     # 0 길이 = "no_non_reject_v4_candidate" 신호 (Step 9 application_plan input).
     v4_candidates: list = field(default_factory=list)
 
+    # IMP-30 u2 — provisional first-render flag. True when the V4Match
+    # backing this unit was synthesized via lookup_v4_match_with_fallback
+    # (allow_provisional=True) after chain_exhausted, or when u3 inserts
+    # a last-resort provisional fill for an uncovered section. Carried as
+    # data (not re-derived from label/selection_path downstream) so the
+    # render path / status / zone template can surface "needs adaptation"
+    # uniformly. Default False keeps non-provisional units byte-identical.
+    provisional: bool = False
+
 
 # ─── Heading Tree ──────────────────────────────────────────────
 
@@ -490,6 +499,7 @@ def collect_candidates(sections, v4_lookup_fn, v4_label_to_status: dict,
             raw_content=s.raw_content,
             title=s.title,
             v4_candidates=_v4_cands(s.section_id),
+            provisional=getattr(match, "provisional", False),
         )
         _apply_capacity_fit(c, capacity_fit_fn)
         candidates.append(c)
@@ -524,6 +534,7 @@ def collect_candidates(sections, v4_lookup_fn, v4_label_to_status: dict,
             raw_content=merged_raw,
             title=pid,
             v4_candidates=_v4_cands(pid),
+            provisional=getattr(parent_match, "provisional", False),
         )
         _apply_capacity_fit(c_pm, capacity_fit_fn)
         candidates.append(c_pm)
@@ -624,6 +635,10 @@ def collect_candidates(sections, v4_lookup_fn, v4_label_to_status: dict,
             notes=notes,
             # rep_child 의 V4 후보 list (rep_match 와 같은 출처, frame_* 와 일관).
             v4_candidates=_v4_cands(rep_child.section_id),
+            # IMP-30 u2 — rep_match drives frame selection so its provisional
+            # flag flows here. If a non-rep child match is provisional but the
+            # rep is not, this unit is not provisional (the rep frame is real).
+            provisional=getattr(rep_match, "provisional", False),
         )
         _apply_capacity_fit(c_inf, capacity_fit_fn)
         candidates.append(c_inf)
@@ -670,7 +685,13 @@ def score_candidate(c: CompositionUnit) -> CompositionUnit:
 
 # ─── Selection ─────────────────────────────────────────────────
 
-def select_composition_units(candidates, allowed_statuses: set[str]) -> list[CompositionUnit]:
+def select_composition_units(
+    candidates,
+    allowed_statuses: set[str],
+    *,
+    all_section_ids: Optional[list[str]] = None,
+    allow_provisional_fill: bool = False,
+) -> list[CompositionUnit]:
     """Greedy non-overlapping selection by score, with coverage tiebreak.
 
     1. 모든 candidate 점수 매김
@@ -685,6 +706,27 @@ def select_composition_units(candidates, allowed_statuses: set[str]) -> list[Com
 
     auto_selectable=False candidate 는 자동 선택 X. debug 의 candidates_summary 에는 남음.
     UI/editor layer 에서 사용자가 별도 처리 가능 (현 v0 범위 X).
+
+    IMP-30 u3 — last-resort provisional fill (opt-in via allow_provisional_fill):
+      After the normal greedy pass, sections in ``all_section_ids`` that are
+      still uncovered are filled with the highest-score *provisional*
+      candidate (``c.provisional == True``) that includes at least one
+      uncovered section and does not collide with already-covered ones. A
+      provisional candidate's backing V4Match was synthesized via
+      ``lookup_v4_match_with_fallback(allow_provisional=True)`` (IMP-30 u1)
+      after chain_exhausted; its ``phase_z_status`` is therefore typically
+      *outside* ``allowed_statuses`` (extract_matched_zone / fallback_candidate),
+      which is why it gets filtered out of the normal greedy pass. The fill
+      preserves first-render invariant for sections whose rank-1~3 are all
+      restructure/reject. Default ``allow_provisional_fill=False`` keeps
+      pre-u3 behavior byte-identical (IMP-05 regression guard).
+
+    Args:
+        candidates: full candidate pool from collect_candidates().
+        allowed_statuses: phase_z_status set considered auto-renderable.
+        all_section_ids: ordered section id list (only consulted when
+            allow_provisional_fill=True; required for coverage check).
+        allow_provisional_fill: opt-in for last-resort provisional fill.
     """
     scored = [score_candidate(c) for c in candidates]
     viable = [
@@ -701,6 +743,28 @@ def select_composition_units(candidates, allowed_statuses: set[str]) -> list[Com
         selected.append(c)
         covered.update(c.source_section_ids)
 
+    # IMP-30 u3 — last-resort provisional fill (opt-in, default off).
+    # Honors first-render invariant by surfacing chain_exhausted sections as
+    # provisional zones instead of dropping them. Skip reasons on
+    # non-provisional filtered candidates are preserved (not mutated here).
+    if allow_provisional_fill and all_section_ids:
+        uncovered = {sid for sid in all_section_ids if sid not in covered}
+        if uncovered:
+            provisional_pool = [
+                c for c in scored
+                if c.provisional
+                and any(sid in uncovered for sid in c.source_section_ids)
+            ]
+            provisional_pool.sort(
+                key=lambda c: (c.score, len(c.source_section_ids)),
+                reverse=True,
+            )
+            for c in provisional_pool:
+                if any(sid in covered for sid in c.source_section_ids):
+                    continue
+                selected.append(c)
+                covered.update(c.source_section_ids)
+
     return selected
 
 
@@ -740,7 +804,9 @@ def select_layout_preset(units: list[CompositionUnit]) -> Optional[str]:
 def plan_composition(sections, v4_lookup_fn, v4_label_to_status: dict,
                      allowed_statuses: set[str],
                      capacity_fit_fn=None,
-                     v4_candidates_lookup_fn=None) -> tuple[list[CompositionUnit], Optional[str], dict]:
+                     v4_candidates_lookup_fn=None,
+                     *,
+                     allow_provisional_fill: bool = False) -> tuple[list[CompositionUnit], Optional[str], dict]:
     """Composition planner v0.2 entry.
 
     v0.2 변경 :
@@ -753,6 +819,14 @@ def plan_composition(sections, v4_lookup_fn, v4_label_to_status: dict,
         logic 변화 X — 단일 frame_template_id / frame_id / label / confidence 는 그대로.
         runtime 결과 무변. Step 9 application_plan input 위한 schema 확장.
 
+    IMP-30 u3 — last-resort provisional fill (opt-in, default off):
+      ``allow_provisional_fill`` is plumbed to select_composition_units().
+      When True, uncovered sections receive a provisional fill from candidates
+      whose backing V4Match was synthesized via ``allow_provisional=True``
+      (IMP-30 u1). ``_candidate_state`` returns ``selected_provisional`` for
+      those filled units so the debug summary distinguishes greedy selections
+      from provisional fills. Default False keeps IMP-05 behavior identical.
+
     v0.1 / v0.1.1 동작 (유지) :
       - parent_merged_inferred candidate 생성 (parent V4 없어도)
       - review 개념 X. auto_selectable + filter_reasons 만으로 자동 결정
@@ -771,11 +845,22 @@ def plan_composition(sections, v4_lookup_fn, v4_label_to_status: dict,
     )
     scored_all = [score_candidate(c) for c in candidates]
 
-    units = select_composition_units(candidates, allowed_statuses)
+    units = select_composition_units(
+        candidates,
+        allowed_statuses,
+        all_section_ids=[s.section_id for s in sections] if allow_provisional_fill else None,
+        allow_provisional_fill=allow_provisional_fill,
+    )
     preset = select_layout_preset(units)
 
     def _candidate_state(c: CompositionUnit) -> str:
         if c in units:
+            # IMP-30 u3 — provisional-fill units surface as a distinct state so
+            # downstream debug consumers can tell greedy selection apart from
+            # last-resort fill. unit.provisional flows from u1 (V4Match
+            # synthesis) → u2 (CompositionUnit propagation).
+            if c.provisional:
+                return "selected_provisional"
             return "selected"
         if c.phase_z_status not in allowed_statuses:
             return "filtered_status"               # V4 label → status not auto-renderable

src/phase_z2_pipeline.py

@@ -176,6 +176,12 @@ class V4Match:
     v4_rank: Optional[int] = None
     selection_path: str = "rank_1"
     fallback_reason: Optional[str] = None
+    # IMP-30 u1 — provisional first-render flag. True when the selector
+    # synthesizes a rank-1 V4 candidate after chain_exhausted because the
+    # opt-in allow_provisional kwarg was set. Default False keeps IMP-05
+    # behavior byte-identical; downstream surfaces this for zone-level
+    # "needs adaptation" marking without altering V4 evidence.
+    provisional: bool = False
 
 
 def to_phase_z_status(match: V4Match) -> str:
@@ -585,11 +591,26 @@ def lookup_v4_match_with_fallback(
     raw_content: Optional[str] = None,
     max_rank: int = 3,
     alias_keys: Optional[list] = None,
+    allow_provisional: bool = False,
 ) -> tuple[Optional[V4Match], dict]:
     """Select V4 rank-1, or promote rank-2/3 when rank-1 is not auto-renderable.
 
     This is an IMP-05 selector only. It uses existing V4 labels, frame-contract
     presence, and the Phase Z capacity precheck; it does not call calculate_fit.
+
+    IMP-30 u1 — when ``allow_provisional=True`` and the rank-1..max_rank chain
+    is exhausted (no candidate passes MVP1 filter + contract + capacity), the
+    selector synthesizes a *provisional* V4Match from the rank-1 judgment so
+    the first-render invariant can be satisfied downstream. The synthesized
+    match carries ``provisional=True``, ``selection_path="provisional_rank_1"``,
+    and ``fallback_reason`` mirrors the existing chain-exhaust reason. The
+    candidate trace shape is unchanged (synthetic injection only updates the
+    top-level ``selection_path`` + ``selected_*`` mirrors). When the rank-1
+    judgment itself is missing (``empty_v4_judgments`` / ``no_v4_section``),
+    no provisional is synthesized — the caller (u3 / u4) handles those cases
+    with a placeholder zone or empty-shell.
+
+    Default ``allow_provisional=False`` keeps the IMP-05 behavior byte-identical.
     """
     resolved = _resolve_v4_section_key(v4, section_id, alias_keys=alias_keys)
     sec = v4.get("mdx_sections", {}).get(resolved) if resolved else None
@@ -692,6 +713,32 @@ def lookup_v4_match_with_fallback(
 
     trace["selection_path"] = "chain_exhausted"
     trace["fallback_reason"] = first_skip_reason or "no_auto_renderable_rank_1_to_3"
+
+    # IMP-30 u1 — opt-in provisional first-render synthesis. When the caller
+    # signals allow_provisional, promote rank-1 judgment as a provisional
+    # match so downstream composition can satisfy the first-render invariant.
+    # Top-level mirrors (selection_path / selected_*) are updated; candidate
+    # trace entries are left intact (their skip reasons remain accurate).
+    # Default-off keeps IMP-05 behavior byte-identical.
+    if allow_provisional:
+        rank_1_judgment = judgments[0]
+        provisional_match = _v4_match_from_judgment(
+            section_id, rank_1_judgment, rank=1
+        )
+        provisional_match.selection_path = "provisional_rank_1"
+        provisional_match.fallback_reason = trace["fallback_reason"]
+        provisional_match.provisional = True
+        trace.update({
+            "selection_path": "provisional_rank_1",
+            "selected_rank": 1,
+            "selected_template_id": provisional_match.template_id,
+            "selected_frame_id": provisional_match.frame_id,
+            "selected_label": provisional_match.label,
+            "fallback_used": True,
+            "provisional": True,
+        })
+        return provisional_match, trace
+
     return None, trace
 
 
@@ -2437,6 +2484,9 @@ def compute_slide_status(sections: list[MdxSection],
       - full_mdx_coverage   : aligned 된 모든 section_id 가 어떤 selected unit 에 의해 covered
       - adapter_needed_count : mapper FitError 로 자동 렌더 못 한 unit 수 (별 review 개념 X — 자동 실패 보고)
       - content_truncated_count : builder 가 truncate 한 zone 수 (informational)
+      - provisional_first_render_count : IMP-30 first-render invariant 로 합성된 unit 수
+                                         (u1 V4Match synthesis / u3 last-resort fill /
+                                         u4 empty-shell — needs user/AI adaptation 신호)
 
     overall enum :
       PASS                                    — visual OK + full coverage + adapter_needed=0
@@ -2444,6 +2494,8 @@ def compute_slide_status(sections: list[MdxSection],
       PARTIAL_COVERAGE                        — 일부 section 필터됨, 렌더된 부분만 visual OK
       PARTIAL_COVERAGE_WITH_VISUAL_REGRESSION — 둘 다
       (adapter_needed > 0 시 status note 추가, overall 은 위 enum 사용)
+      (IMP-30 u6 : provisional_first_render_count 도 qualifier 일 뿐, overall enum 변경 X.
+       Stage 1 Q3 + Codex #10 D4 lock.)
     """
     aligned_ids = [s.section_id for s in sections]
     covered = set()
@@ -2555,6 +2607,29 @@ def compute_slide_status(sections: list[MdxSection],
     _fallback_selection_count = _v4_fb_summary.get("fallback_selection_count", 0)
     _selection_paths = _v4_fb_summary.get("selection_paths", [])
 
+    # IMP-30 u6 — Step 20 additive qualifier fields for the first-render invariant.
+    # provisional_first_render_count = number of selected units whose .provisional
+    # flag is True (set by u1 V4Match synthesis → u2 CompositionUnit propagation,
+    # u3 last-resort fill, or u4 empty-shell synthesis). The list mirrors the shape
+    # of fallback_selections / adapter_needed_units for symmetry. Top-level overall
+    # enum stays unchanged per IMP-05 Codex #10 D4 + Stage 1 Q3 decision: this
+    # signal is a qualifier, not a new failure class. Defensive getattr keeps the
+    # function safe when units come from legacy code paths predating u2.
+    provisional_first_render_units: list[dict] = []
+    for u in units:
+        if not getattr(u, "provisional", False):
+            continue
+        provisional_first_render_units.append({
+            "source_section_ids": list(getattr(u, "source_section_ids", []) or []),
+            "phase_z_status": getattr(u, "phase_z_status", None),
+            "frame_template_id": getattr(u, "frame_template_id", None),
+            "frame_id": getattr(u, "frame_id", None),
+            "label": getattr(u, "label", None),
+            "selection_path": getattr(u, "selection_path", None),
+            "fallback_reason": getattr(u, "fallback_reason", None),
+            "v4_rank": getattr(u, "v4_rank", None),
+        })
+
     return {
         "rendered": True,
         "visual_check_passed": visual_passed,
@@ -2574,12 +2649,17 @@ def compute_slide_status(sections: list[MdxSection],
         "adapter_needed_units": adapter_needed_units,
         "content_truncated_count": len(content_truncated),
         "content_truncated_units": content_truncated,
+        # IMP-30 u6 — additive provisional qualifiers (overall enum unchanged).
+        "provisional_first_render_count": len(provisional_first_render_units),
+        "provisional_first_render_units": provisional_first_render_units,
         "overall": overall,
         "note": (
             "자동 파이프라인 결과 보고. review/UI 개념 X. final.html 파일명 != PASS 의미. "
             "overall == PASS 는 visual OK + full coverage + adapter_needed=0 일 때만. "
             "adapter_needed_count > 0 = mapper 가 contract 와 안 맞아 자동 렌더 못 한 zone 존재. "
-            "content_truncated_count > 0 = builder 가 truncate 한 zone 존재 (rendered 됐지만 일부 콘텐츠 손실)."
+            "content_truncated_count > 0 = builder 가 truncate 한 zone 존재 (rendered 됐지만 일부 콘텐츠 손실). "
+            "provisional_first_render_count > 0 = IMP-30 first-render invariant 가 작동한 unit 존재 "
+            "(empty_shell / chain_exhausted_provisional / 등 — needs user/AI adaptation)."
         ),
     }
 
@@ -3154,25 +3234,145 @@ def run_phase_z2_mvp1(
         units = plan_units
 
     if not units or layout_preset is None:
-        # composition planner 결과 = 0 units. Sections 가 모두 V4 lookup 실패 또는
-        # status filter 통과 못 함. error.json 기록 후 abort.
-        run_dir.mkdir(parents=True, exist_ok=True)
-        error_data = {
-            "stage": "composition_planner",
-            "reason": (
-                "Composition planner v0 selected 0 viable units. "
-                f"Either no V4 entries for any section, or all candidates filtered out by "
-                f"allowed_statuses={sorted(MVP1_ALLOWED_STATUSES)}."
-            ),
-            "aligned_section_ids": [s.section_id for s in sections],
-            "composition_debug": comp_debug,
-        }
-        err_path = run_dir / "error.json"
-        err_path.write_text(json.dumps(error_data, ensure_ascii=False, indent=2), encoding="utf-8")
-        print(f"\n[Phase Z-2 MVP-1.5b] ABORT @ composition_planner", file=sys.stderr)
-        print(f"  reason  : 0 viable units after composition v0", file=sys.stderr)
-        print(f"  error   : {err_path}", file=sys.stderr)
-        sys.exit(1)
+        # IMP-30 u4 — first-render invariant. The pre-u4 path here was
+        # `sys.exit(1)` after writing error.json. That violated the invariant
+        # ("final.html + Step 20 slide_status MUST be written for every input
+        # where Step 0~5 succeed") whenever V4 evidence for any section was
+        # restructure/reject (chain_exhausted) or missing (no_v4_section /
+        # empty_v4_judgments).
+        #
+        # Recovery has two phases:
+        #   Phase A — provisional retry (u1 + u3 opt-in). Re-run plan_composition
+        #     with allow_provisional=True (in lookup_fn) and allow_provisional_fill
+        #     =True. Synthesizes rank-1 provisional V4Match on chain_exhausted
+        #     (u1) and last-resort-fills uncovered sections with provisional
+        #     candidates (u3). Skipped when the CLI override path was used —
+        #     re-running plan_composition there would discard the override.
+        #   Phase B — terminal empty-shell. If retry still yields zero units
+        #     (true "no rank-1 V4 anywhere" case, or override path with no
+        #     resolvable assignments), synthesize a single placeholder
+        #     CompositionUnit with frame_template_id="__empty__", layout_preset
+        #     ="single". The per-unit loop's __empty__ guard emits a placeholder
+        #     zones_data / debug_zones record; final.html renders the slide
+        #     base shell (title + footer + empty zone) so the first-render
+        #     invariant holds. Provisional flag = True surfaces the "needs
+        #     adaptation" signal (u5 zone class + u6 status qualifier).
+        provisional_recovered = False
+        if section_assignment_plan is None:
+            def _lookup_fn_provisional(sid: str) -> Optional[V4Match]:
+                match, trace = lookup_v4_match_with_fallback(
+                    v4,
+                    sid,
+                    raw_content=section_content_by_id.get(sid),
+                    max_rank=3,
+                    alias_keys=section_alias_by_id.get(sid),
+                    allow_provisional=True,
+                )
+                v4_fallback_traces[sid] = trace
+                return match
+
+            units_retry, layout_preset_retry, comp_debug_retry = plan_composition(
+                sections,
+                _lookup_fn_provisional,
+                V4_LABEL_TO_PHASE_Z_STATUS,
+                MVP1_ALLOWED_STATUSES,
+                capacity_fit_fn=compute_capacity_fit,
+                v4_candidates_lookup_fn=candidates_lookup_fn,
+                allow_provisional_fill=True,
+            )
+            comp_debug["imp30_u4_provisional_retry"] = {
+                "applied": True,
+                "result_unit_count": len(units_retry),
+                "result_layout_preset": layout_preset_retry,
+                "candidates_summary": comp_debug_retry.get("candidates_summary"),
+            }
+            if units_retry and layout_preset_retry is not None:
+                units = units_retry
+                layout_preset = layout_preset_retry
+                provisional_recovered = True
+                # v4_fallback_traces was overwritten by _lookup_fn_provisional;
+                # refresh the IMP-05 selection_paths telemetry so Step 20 reflects
+                # the actual selection (provisional_rank_1) rather than the stale
+                # chain_exhausted state from the first attempt.
+                _imp05_selection_paths_retry = [
+                    {
+                        "section_id": sid,
+                        "selection_path": t.get("selection_path"),
+                        "selected_rank": t.get("selected_rank"),
+                        "selected_template_id": t.get("selected_template_id"),
+                        "fallback_trigger": (
+                            t.get("fallback_reason") if t.get("fallback_used") else None
+                        ),
+                    }
+                    for sid, t in v4_fallback_traces.items()
+                ]
+                comp_debug["v4_fallback_selections"] = list(v4_fallback_traces.values())
+                if "v4_fallback_summary" in comp_debug:
+                    comp_debug["v4_fallback_summary"]["selection_paths"] = (
+                        _imp05_selection_paths_retry
+                    )
+                print(
+                    f"  [IMP-30 u4] provisional retry recovered {len(units)} unit(s) "
+                    f"— first-render invariant preserved.",
+                    file=sys.stderr,
+                )
+
+        if not provisional_recovered:
+            # Phase B — terminal empty-shell. No rank-1 V4 evidence for any
+            # section, or override path produced no renderable assignments.
+            from src.phase_z2_composition import CompositionUnit as _CompositionUnit
+            run_dir.mkdir(parents=True, exist_ok=True)
+            empty_shell_unit = _CompositionUnit(
+                source_section_ids=[s.section_id for s in sections],
+                merge_type="empty_shell",
+                frame_template_id="__empty__",
+                frame_id="__empty__",
+                frame_number=0,
+                confidence=0.0,
+                label="empty_shell",
+                phase_z_status="empty_shell",
+                raw_content="\n\n".join((s.raw_content or "") for s in sections),
+                title=" / ".join((s.title or "") for s in sections),
+                v4_rank=None,
+                selection_path="empty_shell",
+                fallback_reason="no_v4_rank_1_for_any_section",
+                score=0.0,
+                rationale={
+                    "imp30_u4": "terminal_first_render_empty_shell",
+                    "reason": (
+                        "no_rank_1_V4_evidence_in_any_section"
+                        if section_assignment_plan is None
+                        else "section_assignment_override_yielded_no_renderable_units"
+                    ),
+                    "aligned_section_ids": [s.section_id for s in sections],
+                },
+                provisional=True,
+            )
+            units = [empty_shell_unit]
+            layout_preset = "single"
+            comp_debug["imp30_u4_empty_shell"] = {
+                "applied": True,
+                "reason": (
+                    "no_rank_1_V4_for_any_section"
+                    if section_assignment_plan is None
+                    else "section_assignment_override_yielded_no_renderable_units"
+                ),
+                "aligned_section_ids": [s.section_id for s in sections],
+            }
+            print(
+                f"\n[Phase Z-2 IMP-30 u4] EMPTY-SHELL @ composition_planner",
+                file=sys.stderr,
+            )
+            print(
+                f"  reason : "
+                f"{'no rank-1 V4 evidence for any section' if section_assignment_plan is None else 'override produced no renderable units'}",
+                file=sys.stderr,
+            )
+            print(
+                f"  shell  : 1 placeholder unit, preset='single' "
+                f"(sections={[s.section_id for s in sections]})",
+                file=sys.stderr,
+            )
 
     print(f"  preset  : {layout_preset} ({len(units)} units, composition v0 count-based)")
     for u in units:
@@ -3345,6 +3545,63 @@ def run_phase_z2_mvp1(
         # and is byte-identical to plan_record.position in the normal case.
         if plan_record is not None and plan_record.get("position"):
             position = plan_record["position"]
+
+        # IMP-30 u4 — empty-shell synthesized unit. frame_template_id="__empty__"
+        # has no catalog contract by design; bypass mapper/contract path and emit
+        # a placeholder zone record so render_slide() short-circuits to empty
+        # partial_html (existing `__empty__` branch at render_slide:2106). The
+        # slide_base still renders title + footer + empty grid cell so the
+        # first-render invariant holds; u5 will surface the provisional flag as
+        # a zone class + needs-adaptation badge.
+        if unit.frame_template_id == "__empty__":
+            zones_data.append({
+                "position": position,
+                "template_id": "__empty__",
+                "slot_payload": {},
+                "content_weight": {"score": 0},
+                "min_height_px": 0,
+                "assignment_source": "imp30_u4_empty_shell",
+                "section_assignment_override": False,
+                "provisional": bool(getattr(unit, "provisional", False)),
+            })
+            debug_zones.append({
+                "position": position,
+                "source_section_ids": list(unit.source_section_ids),
+                "merge_type": unit.merge_type,
+                "title": unit.title,
+                "v4_rank1_frame_id": unit.frame_id,
+                "v4_rank1_frame_number": unit.frame_number,
+                "v4_template_id": "__empty__",
+                "v4_label": unit.label,
+                "v4_confidence": float(unit.confidence or 0.0),
+                "v4_selected_rank": unit.v4_rank,
+                "selection_path": unit.selection_path,
+                "fallback_reason": unit.fallback_reason,
+                "fallback_used": False,
+                "phase_z_status": unit.phase_z_status,
+                "composition_score": float(unit.score or 0.0),
+                "composition_rationale": dict(unit.rationale or {}),
+                "composition_notes": list(unit.notes),
+                "mapper_type": "empty_shell",
+                "contract_id": "__empty__",
+                "contract_frame_id": None,
+                "builder": None,
+                "min_height_px": 0,
+                "slot_payload_keys": [],
+                "content_truncated_count": None,
+                "assets_dir": None,
+                "content_weight": {"score": 0},
+                "placement_trace": None,
+                "assignment_source": "imp30_u4_empty_shell",
+                "section_assignment_override": False,
+                "replaced_auto_unit": None,
+                "skipped_collided_auto_units": [],
+                "uncovered_section_ids": [],
+                "skipped_reason": "imp30_u4_empty_shell_no_v4_evidence",
+                "provisional": bool(getattr(unit, "provisional", False)),
+            })
+            continue
+
         synth_section = MdxSection(
             section_id="+".join(unit.source_section_ids),
             section_num=0,
@@ -3470,6 +3727,12 @@ def run_phase_z2_mvp1(
             plan_record.get("skipped_reason") if plan_record else None
         )
 
+        # IMP-30 u5 — `provisional` flag flows as data through V4Match (u1) →
+        # CompositionUnit (u2) → zones_data here. slide_base.html reads
+        # zone.provisional to apply the `zone--provisional` class + inline
+        # needs-adaptation badge. Default False keeps non-provisional zones
+        # byte-identical to pre-u5; only u1-synthesized rank-1 fills or u4
+        # empty-shell synthesize provisional=True units.
         zones_data.append({
             "position": position,
             "template_id": unit.frame_template_id,
@@ -3478,6 +3741,7 @@ def run_phase_z2_mvp1(
             "min_height_px": min_height_px,
             "assignment_source": plan_assignment_source,
             "section_assignment_override": plan_section_override,
+            "provisional": bool(getattr(unit, "provisional", False)),
         })
         debug_zones.append({
             "position": position,
@@ -3515,6 +3779,8 @@ def run_phase_z2_mvp1(
             "skipped_collided_auto_units": plan_skipped_collided,
             "uncovered_section_ids": plan_uncovered,
             "skipped_reason": plan_skipped_reason,
+            # IMP-30 u5 — provisional signal mirror for debug.json consumers.
+            "provisional": bool(getattr(unit, "provisional", False)),
         })
 
     # IMP-06 blocker-fix (Codex #10 Catch N) — append explicit empty zone records

templates/phase_z2/slide_base.html

@@ -114,6 +114,43 @@
       min-height: 0;
     }
 
+    /* ── IMP-30 u5 : provisional zone marker (first-render invariant) ──
+         When V4 rank-1 candidate falls outside MVP1_ALLOWED_STATUSES (chain_exhausted)
+         the pipeline still renders the rank-1 frame so the first-render invariant
+         holds, but the zone is tagged `provisional` so the user/AI can adapt later
+         (IMP-31). Visual contract:
+           - dashed amber border + striped wash → "needs adaptation" at a glance
+           - inline badge top-right → text label for non-color-perceiving readers
+         MDX content is preserved as-is; no shrink, no rewrite. */
+    .zone--provisional {
+      outline: 2px dashed #b8860b;
+      outline-offset: -2px;
+      background-image: repeating-linear-gradient(
+        45deg,
+        rgba(184, 134, 11, 0.04) 0,
+        rgba(184, 134, 11, 0.04) 8px,
+        transparent 8px,
+        transparent 16px
+      );
+    }
+    .zone--provisional .zone__needs-adaptation-badge {
+      position: absolute;
+      top: 4px;
+      right: 4px;
+      z-index: 10;
+      padding: 2px 6px;
+      background: #b8860b;
+      color: #fff;
+      font-size: 9px;
+      font-weight: 700;
+      line-height: 1.2;
+      letter-spacing: 0.04em;
+      border-radius: 2px;
+      text-transform: uppercase;
+      pointer-events: none;
+      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.15);
+    }
+
     /* ── Frame-family text layout contract (shared, reusable) ──
          feedback-1 (mvp1.5b_test7): visible improvement 강화.
          Stronger hanging indent + breathing line spacing + visible hierarchy. */
@@ -264,7 +301,8 @@
     <div class="slide-body">
       <div class="layout-{{ layout_preset }}">
         {% for zone in zones %}
-        <div class="zone" data-zone-position="{{ zone.position }}" data-template-id="{{ zone.template_id }}" style="grid-area: {{ zone.position }};">
+        <div class="zone{% if zone.provisional %} zone--provisional{% endif %}" data-zone-position="{{ zone.position }}" data-template-id="{{ zone.template_id }}"{% if zone.provisional %} data-provisional="1"{% endif %} style="grid-area: {{ zone.position }};">
+          {% if zone.provisional %}<span class="zone__needs-adaptation-badge" aria-label="needs user or AI adaptation">needs adaptation</span>{% endif %}
           {{ zone.partial_html | safe }}
         </div>
         {% endfor %}

tests/orchestrator_unit/test_imp17_comment_anchor.py

@@ -4,6 +4,10 @@ Stage 1 finding: line 564 previously referenced a non-existent ID ("IMP-31").
 The legitimate slot is IMP-17 (Gitea #17, carve-out — AI fallback only, normal path 밖).
 Line 565 (IMP-29 frontend zone-level override) must remain untouched.
 
+Anchor re-pin (2026-05-20, IMP-30 u1 follow-up): V4Match.provisional field added at
+src/phase_z2_pipeline.py:179-184 shifted the route-hint table down by six lines.
+Pinned line numbers updated from 564/565 → 570/571 to track the actual anchor location.
+
 Run: pytest -q tests/orchestrator_unit/test_imp17_comment_anchor.py
 """
 from pathlib import Path
@@ -16,14 +20,14 @@ def _lines() -> list[str]:
     return PIPELINE.read_text(encoding="utf-8").splitlines()
 
 
-def test_line_564_references_imp17_not_imp31():
-    line = _lines()[563]  # 1-indexed line 564
-    assert "restructure" in line, f"line 564 anchor drifted: {line!r}"
-    assert "IMP-17" in line, f"line 564 must reference IMP-17 (carve-out): {line!r}"
-    assert "IMP-31" not in line, f"line 564 must not reference non-existent IMP-31: {line!r}"
+def test_line_570_references_imp17_not_imp31():
+    line = _lines()[569]  # 1-indexed line 570
+    assert "restructure" in line, f"line 570 anchor drifted: {line!r}"
+    assert "IMP-17" in line, f"line 570 must reference IMP-17 (carve-out): {line!r}"
+    assert "IMP-31" not in line, f"line 570 must not reference non-existent IMP-31: {line!r}"
 
 
-def test_line_565_still_references_imp29():
-    line = _lines()[564]  # 1-indexed line 565
-    assert "reject" in line, f"line 565 anchor drifted: {line!r}"
-    assert "IMP-29" in line, f"line 565 must still reference IMP-29 frontend override: {line!r}"
+def test_line_571_still_references_imp29():
+    line = _lines()[570]  # 1-indexed line 571
+    assert "reject" in line, f"line 571 anchor drifted: {line!r}"
+    assert "IMP-29" in line, f"line 571 must still reference IMP-29 frontend override: {line!r}"

tests/test_phase_z2_v4_fallback.py

@@ -380,3 +380,125 @@ def test_step20_slide_status_qualifier_fields_present_with_defensive_defaults():
     # Defensive defaults — 0 + [] when summary present but empty
     assert status_c["fallback_selection_count"] == 0
     assert status_c["selection_paths"] == []
+
+
+# ─── Case 9 : IMP-30 u1 — opt-in provisional synthesis on chain_exhausted ───
+
+
+def test_allow_provisional_default_off_preserves_imp05_behavior(patch_selector_deps):
+    """IMP-30 u1 — default ``allow_provisional=False`` keeps chain_exhausted
+    returning ``(None, trace)`` exactly as IMP-05 specified. Regression guard
+    for IMP-05 close commit 23d1b25.
+    """
+    v4 = _make_v4([
+        _j(1, "MOCK_template_restructure_a", "MOCK_frame_001", "restructure"),
+        _j(2, "MOCK_template_reject_a", "MOCK_frame_002", "reject"),
+    ])
+
+    match, trace = lookup_v4_match_with_fallback(
+        v4, "S1", raw_content="- a\n- b\n- c\n"
+    )
+
+    assert match is None
+    assert trace["selection_path"] == "chain_exhausted"
+    assert trace.get("provisional") is None
+    assert trace["selected_rank"] is None
+    assert trace["selected_template_id"] is None
+
+
+def test_allow_provisional_synthesizes_rank_1_on_chain_exhausted(patch_selector_deps):
+    """IMP-30 u1 — opt-in ``allow_provisional=True`` synthesizes a provisional
+    rank-1 match when the rank-1..3 chain is exhausted (all restructure/reject).
+    Downstream first-render invariant uses this to render a "needs adaptation"
+    zone instead of aborting.
+    """
+    v4 = _make_v4([
+        _j(1, "MOCK_template_restructure_a", "MOCK_frame_001", "restructure"),
+        _j(2, "MOCK_template_reject_a", "MOCK_frame_002", "reject"),
+    ])
+
+    match, trace = lookup_v4_match_with_fallback(
+        v4, "S1", raw_content="- a\n- b\n- c\n",
+        allow_provisional=True,
+    )
+
+    # Provisional rank-1 synthesized from the rank-1 judgment
+    assert match is not None
+    assert match.provisional is True
+    assert match.template_id == "MOCK_template_restructure_a"
+    assert match.frame_id == "MOCK_frame_001"
+    assert match.label == "restructure"
+    assert match.v4_rank == 1
+    assert match.selection_path == "provisional_rank_1"
+    # fallback_reason mirrors the chain-exhaust reason
+    assert match.fallback_reason is not None
+    assert "phase_z_status_not_allowed" in match.fallback_reason
+
+    # Top-level trace mirrors reflect provisional selection
+    assert trace["selection_path"] == "provisional_rank_1"
+    assert trace["selected_rank"] == 1
+    assert trace["selected_template_id"] == "MOCK_template_restructure_a"
+    assert trace["selected_frame_id"] == "MOCK_frame_001"
+    assert trace["selected_label"] == "restructure"
+    assert trace["fallback_used"] is True
+    assert trace["provisional"] is True
+
+    # Original candidate skip reasons are preserved (not rewritten by synthesis)
+    by_rank = {c["rank"]: c for c in trace["candidates"]}
+    assert by_rank[1]["decision"] == "skipped"
+    assert by_rank[1]["reason"] == "phase_z_status_not_allowed:extract_matched_zone"
+    assert by_rank[2]["decision"] == "skipped"
+    assert by_rank[2]["reason"] == "phase_z_status_not_allowed:fallback_candidate"
+
+
+def test_allow_provisional_no_op_when_normal_selection_succeeds(patch_selector_deps):
+    """IMP-30 u1 — ``allow_provisional=True`` is a no-op when normal selection
+    succeeds. The rank-1 (or rank-N fallback) result MUST be non-provisional.
+    """
+    v4 = _make_v4([
+        _j(1, "MOCK_template_direct_a", "MOCK_frame_001", "use_as_is"),
+    ])
+
+    match, trace = lookup_v4_match_with_fallback(
+        v4, "S1", raw_content="- a\n- b\n- c\n",
+        allow_provisional=True,
+    )
+
+    assert match is not None
+    assert match.provisional is False
+    assert match.selection_path == "rank_1"
+    assert trace["selection_path"] == "rank_1"
+    assert trace.get("provisional") is None
+
+
+def test_allow_provisional_no_op_when_no_v4_section(patch_selector_deps):
+    """IMP-30 u1 — when no V4 section is resolved (no rank-1 judgment to
+    synthesize from), ``allow_provisional=True`` MUST still return
+    ``(None, trace)``. u3/u4 handle this case with a placeholder zone or
+    empty-shell terminal slide.
+    """
+    v4 = {"mdx_sections": {}}  # no section at all
+
+    match, trace = lookup_v4_match_with_fallback(
+        v4, "S1", raw_content="- a\n- b\n- c\n",
+        allow_provisional=True,
+    )
+
+    assert match is None
+    assert trace["fallback_reason"] == "no_v4_section"
+
+
+def test_allow_provisional_no_op_when_empty_judgments(patch_selector_deps):
+    """IMP-30 u1 — when the V4 section exists but ``judgments_full32`` is
+    empty, ``allow_provisional=True`` MUST still return ``(None, trace)``.
+    No synthetic rank-1 can be fabricated from nothing.
+    """
+    v4 = {"mdx_sections": {"S1": {"judgments_full32": []}}}
+
+    match, trace = lookup_v4_match_with_fallback(
+        v4, "S1", raw_content="- a\n- b\n- c\n",
+        allow_provisional=True,
+    )
+
+    assert match is None
+    assert trace["fallback_reason"] == "empty_v4_judgments"