feat: text-layer grounding (extractor authority, guard rescue tier, verifier oracle + hi-DPI crops)

- backend/text_layer.py: PyMuPDF text-layer extraction, fuzzy evidence
  bbox matching, 300-DPI crop rendering, coverage-gap signal
- extractor (classic + agent): TEXT LAYER block appended at call sites;
  grounding guard gains text-layer rescue tier (grounding=text_layer stamp)
- verifier: {text_layer} oracle excerpt + evidence-located hi-DPI crops
  replacing full-page images (fallback preserved, I2 guard intact)
- coverage gaps: text-bearing pages with zero extraction -> failed-scope
  gap findings (agent) / log-only (classic)
- config knobs: TEXT_LAYER_ENABLED/MIN_CHARS/MAX_CHARS, VERIFY_TEXT_MAX_CHARS,
  VERIFY_HI_DPI_CROPS, VERIFY_CROP_DPI, VERIFY_CROP_MARGIN_PTS
- tests: 22 new (text_layer unit, grounding/render, runner-level flow)
Spec: docs/superpowers/specs/2026-08-12-text-layer-grounding-design.md

backend/text_layer.py

@@ -0,0 +1,230 @@
+"""
+text_layer.py - deterministic PDF text-layer extraction (PyMuPDF, no LLM).
+
+Most CAD-produced drawing sets carry a real vector text layer. We extract it
+once per job and feed it to the extractor (grounding), the grounding guard
+(rescue tier), and the wave-5b verifier (text oracle + high-DPI evidence
+crops). Pages below TEXT_LAYER_MIN_CHARS of text are treated as having no
+text layer (scanned/raster sheets stay vision-only).
+
+If PyMuPDF is unavailable the module degrades gracefully: every public
+function returns empty/None, equivalent to TEXT_LAYER_ENABLED=false.
+"""
+
+import re
+from typing import Dict, List, Optional, Tuple
+
+from backend import config
+
+try:  # PyMuPDF >= 1.24 prefers the pymupdf name; fitz works everywhere.
+    import pymupdf as fitz
+except ImportError:  # pragma: no cover - older PyMuPDF
+    try:
+        import fitz
+    except ImportError:  # pragma: no cover - PyMuPDF not installed
+        fitz = None
+
+_warned_unavailable = False
+
+# Word token normalization for evidence matching: lowercase alphanumeric only.
+_TOKEN_RE = re.compile(r"[^a-z0-9]+")
+# Fuzzy match floor: fraction of needle tokens that must align with the page's
+# word sequence for a bbox to count as a confident evidence location.
+_FUZZY_MIN_RATIO = 0.6
+
+
+def _fitz_or_none():
+    """Return the fitz module, logging once if PyMuPDF is missing."""
+    global _warned_unavailable
+    if fitz is None and not _warned_unavailable:
+        print("[TextLayer] PyMuPDF not available - text-layer grounding disabled")
+        _warned_unavailable = True
+    return fitz
+
+
+def extract_text_layers(pdf_path: str) -> Dict[int, Dict]:
+    """
+    Extract the text layer of every page. Returns {1-based page_number:
+    {"text": str, "words": [{"text", "bbox": (x0,y0,x1,y1)}, ...],
+    "has_text_layer": bool}}. Returns {} when disabled or unavailable.
+    """
+    if not config.TEXT_LAYER_ENABLED:
+        return {}
+    f = _fitz_or_none()
+    if f is None:
+        return {}
+    try:
+        doc = f.open(pdf_path)
+    except Exception as exc:
+        print(f"[TextLayer] could not open {pdf_path}: {exc}")
+        return {}
+    layers: Dict[int, Dict] = {}
+    try:
+        for index in range(doc.page_count):
+            page = doc[index]
+            text = page.get_text("text") or ""
+            words = [
+                {"text": w[4], "bbox": (w[0], w[1], w[2], w[3])}
+                for w in (page.get_text("words") or [])
+            ]
+            has_text_layer = len(text.strip()) >= config.TEXT_LAYER_MIN_CHARS
+            if not has_text_layer:
+                print(f"[TextLayer] Page {index + 1}: {len(text.strip())} chars "
+                      f"(< TEXT_LAYER_MIN_CHARS={config.TEXT_LAYER_MIN_CHARS}) - "
+                      f"vision-only")
+            layers[index + 1] = {
+                "text": text,
+                "words": words,
+                "has_text_layer": has_text_layer,
+            }
+    finally:
+        doc.close()
+    return layers
+
+
+def attach_text_layers(
+    pdf_path: str,
+    pages: List[Dict],
+    text_dir: Optional[str] = None,
+) -> Dict[int, List[Dict]]:
+    """
+    Attach page["text_layer"] (text or None) to each converted page dict and
+    return the runner-local {page_number: words} map (kept off page dicts -
+    those get serialized). When text_dir is set, dump one .txt per page there
+    (plain file writes; ProjectMemory is a closed registry).
+    """
+    layers = extract_text_layers(pdf_path)
+    page_words: Dict[int, List[Dict]] = {}
+    for page in pages:
+        layer = layers.get(page["page_number"]) or {}
+        page["text_layer"] = layer.get("text") if layer.get("has_text_layer") else None
+        page_words[page["page_number"]] = layer.get("words") or []
+    if text_dir and layers:
+        import os
+        os.makedirs(text_dir, exist_ok=True)
+        for page_number, layer in layers.items():
+            if not layer.get("has_text_layer"):
+                continue
+            with open(os.path.join(text_dir, f"page-{page_number:03d}.txt"),
+                      "w", encoding="utf-8") as fh:
+                fh.write(layer.get("text") or "")
+    return page_words
+
+
+def _tokens(text: str) -> List[str]:
+    return [t for t in _TOKEN_RE.split(text.lower()) if t]
+
+
+def _union_bbox(boxes: List[Tuple[float, float, float, float]]):
+    return (
+        min(b[0] for b in boxes),
+        min(b[1] for b in boxes),
+        max(b[2] for b in boxes),
+        max(b[3] for b in boxes),
+    )
+
+
+def find_evidence_bbox(
+    words: List[Dict],
+    needle: str,
+) -> Optional[Tuple[float, float, float, float]]:
+    """
+    Best-effort fuzzy substring match of an evidence source_text against the
+    page's word sequence. Returns the union bbox of the matched words, or
+    None when nothing aligns confidently.
+
+    Exact contiguous token runs win; otherwise the best-scoring window with
+    >= _FUZZY_MIN_RATIO token alignment is accepted (vision quotes imperfectly
+    but the value is real page text).
+    """
+    if not words or not needle:
+        return None
+    needle_tokens = _tokens(str(needle))
+    if not needle_tokens:
+        return None
+    page_tokens = [_tokens(w.get("text") or "") for w in words]
+    # Flatten multi-token words, remembering which word each token came from.
+    flat: List[Tuple[str, int]] = []
+    for word_index, parts in enumerate(page_tokens):
+        for part in parts:
+            flat.append((part, word_index))
+    if not flat:
+        return None
+
+    n = len(needle_tokens)
+    best_span = None
+    best_score = 0.0
+    for start in range(0, len(flat)):
+        window = flat[start:start + n]
+        if not window:
+            break
+        score = sum(1 for i, tok in enumerate(needle_tokens)
+                    if i < len(window) and window[i][0] == tok) / n
+        if score > best_score:
+            best_score = score
+            best_span = window
+        if best_score == 1.0:
+            break
+    if best_span is None or best_score < _FUZZY_MIN_RATIO:
+        return None
+    word_indexes = {word_index for _, word_index in best_span}
+    return _union_bbox([words[i]["bbox"] for i in sorted(word_indexes)])
+
+
+def render_crop(
+    pdf_path: str,
+    page_number: int,
+    bbox: Tuple[float, float, float, float],
+    dpi: Optional[int] = None,
+    margin_pts: Optional[float] = None,
+) -> Optional[bytes]:
+    """
+    Render a clip of one page around bbox (+ margin, clamped to the page) at
+    the given DPI and return JPEG bytes, or None on any failure.
+    """
+    f = _fitz_or_none()
+    if f is None:
+        return None
+    dpi = dpi or config.VERIFY_CROP_DPI
+    margin_pts = config.VERIFY_CROP_MARGIN_PTS if margin_pts is None else margin_pts
+    try:
+        doc = f.open(pdf_path)
+        try:
+            page = doc[page_number - 1]
+            rect = f.Rect(
+                bbox[0] - margin_pts,
+                bbox[1] - margin_pts,
+                bbox[2] + margin_pts,
+                bbox[3] + margin_pts,
+            ) & page.rect
+            if rect.is_empty:
+                return None
+            pix = page.get_pixmap(clip=rect, dpi=dpi)
+            return pix.tobytes("jpeg")
+        finally:
+            doc.close()
+    except Exception as exc:
+        print(f"[TextLayer] render_crop failed on page {page_number}: {exc}")
+        return None
+
+
+def coverage_gaps(pages: List[Dict], sheets: List[Dict]) -> List[int]:
+    """
+    Page numbers that have a text layer but whose extraction failed or
+    returned 0 objects - the silent extraction-loss signal. Logs one
+    [TextLayer] line per gap.
+    """
+    by_page = {s.get("page_number"): s for s in sheets or []}
+    gaps: List[int] = []
+    for page in pages:
+        text = page.get("text_layer")
+        if not text:
+            continue
+        sheet = by_page.get(page["page_number"])
+        extracted = len(sheet.get("assertions") or []) if sheet else 0
+        if extracted == 0:
+            gaps.append(page["page_number"])
+            print(f"[TextLayer] Page {page['page_number']}: text layer present "
+                  f"({len(text)} chars) but no objects extracted — possible "
+                  f"extraction gap")
+    return gaps