feat(#64): IMP-35 details_popup_escalation u1~u10 + Stage 3 R7 anchor re-pin

Land the production + test surface for the Step 17 cascade POPUP terminal
(DETERMINISTIC -> POPUP -> AI_REPAIR -> USER_OVERRIDE) per Stage 2 plan R2.
u11 (baseline-red invariance gate) was already landed in 7c93031 ahead of
this commit; this commit completes u1~u10 plus the Stage 3 R7 follow-up
anchor re-pin for test_imp17_comment_anchor.py.

Implementation units (Stage 2 R2 contract):
  u1  frame_reselect_insufficient failure_type + post-frame remeasure (q4)
        - src/phase_z2_failure_router.py, src/phase_z2_pipeline.py
  u2  NEXT_ACTION_BY_FAILURE row + impl_status flip
        - src/phase_z2_failure_router.py
  u3  Router details_popup_escalation MISSING->IMPLEMENTED + executor stub
        - src/phase_z2_router.py
  u4  step17.py AI split-decision contract (POPUP cascade_stage +
      route_for_label + skip_reason); API gated
        - src/phase_z2_ai_fallback/step17.py
  u5  Step 17 POPUP gate executor; popup_escalation_plan + has_popup marker
        - src/phase_z2_pipeline.py, src/phase_z2_ai_fallback/step17.py
  u6  Composition popup binding -- yaml strategy -> zone payload
        - src/phase_z2_composition.py
  u7  Pipeline composer -> render_slide wiring
      (popup_html / preview_text / has_popup)
        - src/phase_z2_pipeline.py
  u8  slide_base.html <details>/<summary> popup wrapper
        - templates/phase_z2/slide_base.html
  u9  display_strategies.yaml inline_preview + popup metadata
        - templates/phase_z2/regions/display_strategies.yaml
  u10 MDX preservation invariant: popup=full source / body=summary or subset
        (asserted by tests/phase_z2/test_popup_mdx_preservation.py)
  u11 (already in 7c93031) -- baseline-red invariance gate

Stage 3 R7 follow-up (anchor re-pin, test-only):
  - tests/orchestrator_unit/test_imp17_comment_anchor.py
    Pre-anchor additions in src/phase_z2_pipeline.py (u1 / u5 / u7) shifted
    the restructure/reject route-hint comments 578/579 -> 586/587. Re-pinned
    the two guard tests (and docstring re-pin lineage 564 -> 570 -> 578 ->
    586). Production code untouched.

Verification (Stage 4 R1):
  pytest -q tests/orchestrator_unit/test_imp17_comment_anchor.py
    -> 2 passed / 0.02s
  pytest -q <10 IMP-35 unit files in tests/phase_z2 + tests/phase_z2_ai_fallback>
    -> 136 passed / 15.94s
  Baseline-red invariance gate
    (tests/test_imp47b_step12_ai_wiring.py +
     tests/test_phase_z2_ai_fallback_config.py)
    -> 4 failed / 6 passed; FAILED set === IMP35_BASELINE_RED_NODE_IDS
    (frozen registry from 7c93031). Contract holds.
  Codex Stage 4 R1 = YES (independent verify).

Guardrails honored:
  - MDX content preservation: popup carries full source, body holds
    summary or subset only (CLAUDE.md 자세히보기 원칙;
    feedback_phase_z_spacing_direction -- capacity expanded, no margin shrink).
  - AI isolation contract: Step 17 POPUP gate is deterministic; AI hook
    surface is split-decision contract only, API call gated.
  - No hardcoding: escalation thresholds derived from existing overflow
    detector outputs; preview_chars deterministic from container px.
  - 1 commit = 1 decision unit: u1~u10 land together as the planned
    production surface; u11 was deliberately split into 7c93031 as Stage 3
    R7 carve-out, and the R7 anchor re-pin rides with this commit because
    it is the direct shift consequence of the u1/u5/u7 pre-anchor additions.
  - Scope-locked: .claude/settings.json explicitly excluded
    (Stage 4 exit report contract).

Out of scope (per Stage 1 + Stage 2):
  - AI_REPAIR API activation (post IMP-35 axis).
  - IMP-34 zone resize, IMP-36 responsive fit (chain partners,
    separate issues).
  - Print-time auto-expand JavaScript for <details>.
  - Popup escalation in stages other than Step 17.
  - Baseline-red body repair (4 frozen failures) -- separate follow-up
    issue; u11 only guards the count.
  - frame_reselect algorithm changes (entry point only).
  - templates/phase_z2/slide_base.html path rename.

source_comment_ids:
  Stage 1: claude_stage1_problem_review_imp35, codex_stage1_verification_imp35_yes
  Stage 2: Claude #4 R2 plan, Codex #5 R2 YES
  Stage 3: Claude #86 (R7 anchor re-pin), Codex #87 YES
  Stage 4: Claude #88 R1, Codex #89 R1 YES

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/phase_z2_failure_router.py

@@ -34,8 +34,12 @@ frame_reselect             (V4 top-k 의 다른 frame)
 details_popup_escalation   (가장 invasive — content popup, 마지막 resort)
 ```
 
-`details_popup_escalation` 은 본 매핑에 *없음* — tabular_overflow / structural_major_overflow /
-frame_reselect 실패 이후 단계에서 다룸 (별 step).
+IMP-35 (#64) u2 — cascade terminal landed. `frame_reselect_insufficient`
+(post-frame remeasure failure, classifier path locked in u1) now routes onto
+`details_popup_escalation`. The status table records the popup action as
+MISSING here; the actual executor stub + MISSING→IMPLEMENTED flip lives in
+`src/phase_z2_router.py` (u3 surface), so this module advertises the cascade
+terminal without claiming an implementation it does not own.
 """
 
 from __future__ import annotations
@@ -74,6 +78,13 @@ FAILURE_TYPE_DESCRIPTIONS: dict[str, str] = {
         "font_step_compression salvage step failed — FONT_SIZE_STEPS exhausted "
         "down to the floor without resolving overflow (or text_metrics missing)"
     ),
+    "frame_reselect_insufficient": (
+        "frame_reselect salvage step failed — V4 top-k alternate frame swap "
+        "re-rendered + post-frame remeasure (run_overflow_check) still fails. "
+        "IMP-35 (#64) u1 contract: emitted from salvage_steps[-1].action == "
+        "'frame_reselect' AND passed=False AND post_salvage_overflow present. "
+        "Routes to details_popup_escalation in u2 (cascade terminal)."
+    ),
 }
 
 
@@ -86,6 +97,12 @@ SALVAGE_FAILURE_TYPE_BY_ACTION: dict[str, str] = {
     "cross_zone_redistribute": "cross_zone_redistribute_insufficient",
     "glue_compression":        "glue_absorption_insufficient",
     "font_step_compression":   "font_step_insufficient",
+    # IMP-35 (#64) u1: post-frame remeasure failure. frame_reselect salvage step
+    # writes a salvage_steps entry with action='frame_reselect', passed=False,
+    # and post_salvage_overflow populated by run_overflow_check on the swapped
+    # frame's HTML. classifier reads that entry; u2 adds the NEXT_ACTION row
+    # that routes this onto details_popup_escalation.
+    "frame_reselect":          "frame_reselect_insufficient",
 }
 
 
@@ -98,6 +115,14 @@ NEXT_ACTION_BY_FAILURE: dict[str, str] = {
     "glue_absorption_insufficient":         "font_step_compression",
     "font_step_insufficient":               "layout_adjust",
     "rerender_still_fails":                 "frame_reselect",
+    # IMP-35 (#64) u2 — cascade terminal. frame_reselect salvage exhausted
+    # (post-frame remeasure failed; classifier path gated on
+    # post_salvage_overflow per u1/q4) escalates onto details_popup_escalation.
+    # Popup body holds full MDX source; preview shows summary/subset
+    # (CLAUDE.md 자세히보기 원칙). Executor + MISSING→IMPLEMENTED flip lands
+    # in u3 (src/phase_z2_router.py); this module owns the cascade mapping
+    # only.
+    "frame_reselect_insufficient":          "details_popup_escalation",
     "not_attempted":                        "none",
 }
 
@@ -127,6 +152,12 @@ NEXT_ACTION_RATIONALE: dict[str, str] = {
         "frame/zone 조합 자체 부적합, V4 top-k 의 다른 frame 평가 (frame_reselect). "
         "popup 직행은 아직 빠름 (tabular / structural_major 가 아닌 한)"
     ),
+    "frame_reselect_insufficient": (
+        "V4 top-k frame swap + 명시적 post-frame remeasure 까지 했는데도 overflow "
+        "잔존 → cascade terminal 인 details_popup_escalation 으로 escalate. "
+        "본문 = summary/subset, popup = MDX 원문 (자세히보기 원칙). "
+        "AI repair 진입 전 deterministic 마지막 단계."
+    ),
     "not_attempted": (
         "retry 시도 자체가 없었음 (visual ok 등) — escalation 불필요"
     ),
@@ -145,6 +176,12 @@ NEXT_ACTION_IMPLEMENTATION_STATUS: dict[str, str] = {
     "font_step_compression":   "IMPLEMENTED",  # u6 plan_font_step_compression + apply_font_step_compression_css
     "layout_adjust":           "MISSING",
     "frame_reselect":          "MISSING",
+    # IMP-35 (#64) u2 — cascade terminal advertised as MISSING here. The
+    # router executor stub + MISSING→IMPLEMENTED flip lives in
+    # src/phase_z2_router.py (u3). Keeping this entry as MISSING until u3
+    # lands prevents premature "popup ready" claims from the failure-router
+    # surface.
+    "details_popup_escalation": "MISSING",
     "none":                    "n/a",
 }
 
@@ -170,21 +207,40 @@ def classify_retry_failure(retry_trace: dict) -> Optional[dict]:
     # case 0.7 : salvage chain attempted and ended in a salvage-level failure.
     # zone_ratio_retry 가 먼저 실패한 뒤 _attempt_salvage_chain 이 가동된 path —
     # 마지막 salvage step 의 action 으로 failure_type 을 분류한다. u3 가 routing.
+    #
+    # IMP-35 (#64) u1 — q4 explicit remeasure contract: the frame_reselect
+    # branch is gated on post_salvage_overflow being present on the salvage
+    # step. A bare passed=False flag with no remeasure payload is *not*
+    # sufficient to emit frame_reselect_insufficient (which routes to
+    # details_popup_escalation in u2). When the gate fails, the classifier
+    # falls through to lower-priority cases so the salvage trace surfaces as
+    # an unmatched defensive fallback instead of a spurious popup escalation.
     salvage_steps = retry_trace.get("salvage_steps") or []
     if salvage_steps:
         last = salvage_steps[-1] or {}
         if not last.get("passed"):
             action = (last.get("action") or "").lower()
-            ftype = SALVAGE_FAILURE_TYPE_BY_ACTION.get(action)
-            if ftype is not None:
-                reason = last.get("failure_reason") or ""
-                return {
-                    "failure_type": ftype,
-                    "classification_rule": (
-                        f"salvage_steps[-1].action == {action!r} "
-                        f"AND passed=False. raw failure_reason: {reason!r}"
-                    ),
-                }
+            frame_reselect_blocked = (
+                action == "frame_reselect"
+                and not last.get("post_salvage_overflow")
+            )
+            if not frame_reselect_blocked:
+                ftype = SALVAGE_FAILURE_TYPE_BY_ACTION.get(action)
+                if ftype is not None:
+                    reason = last.get("failure_reason") or ""
+                    rule_suffix = (
+                        " AND post_salvage_overflow present"
+                        if action == "frame_reselect"
+                        else ""
+                    )
+                    return {
+                        "failure_type": ftype,
+                        "classification_rule": (
+                            f"salvage_steps[-1].action == {action!r} "
+                            f"AND passed=False{rule_suffix}. "
+                            f"raw failure_reason: {reason!r}"
+                        ),
+                    }
 
     # case 1 : retry 시도 자체 안 됨 (router_active=False 또는 다른 action)
     if not retry_trace.get("retry_attempted"):