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/config.py

@@ -59,6 +59,18 @@ AGENT_VERIFY_SEVERITIES    = {
 AGENT_VERIFY_REASONING_EFFORT = os.getenv("AGENT_VERIFY_REASONING_EFFORT", "low").strip()
 VERIFY_MAX_TOKENS          = int(os.getenv("VERIFY_MAX_TOKENS", "8192"))
 
+# -- Text-layer grounding (deterministic PDF text layer via PyMuPDF) ----
+# The vector text layer is extracted once per job and grounds the extractor,
+# rescues misquoted-but-real values in the grounding guard, and serves the
+# wave-5b verifier as a text oracle plus high-DPI evidence crops.
+TEXT_LAYER_ENABLED   = os.getenv("TEXT_LAYER_ENABLED", "true").strip().lower() in ("1", "true", "yes")
+TEXT_LAYER_MIN_CHARS = int(os.getenv("TEXT_LAYER_MIN_CHARS", "20"))    # below this per page -> no text layer
+TEXT_LAYER_MAX_CHARS = int(os.getenv("TEXT_LAYER_MAX_CHARS", "12000")) # cap per sheet in extractor prompt
+VERIFY_TEXT_MAX_CHARS = int(os.getenv("VERIFY_TEXT_MAX_CHARS", "8000"))# cap of excerpt in verify scope
+VERIFY_HI_DPI_CROPS  = os.getenv("VERIFY_HI_DPI_CROPS", "true").strip().lower() in ("1", "true", "yes")
+VERIFY_CROP_DPI      = int(os.getenv("VERIFY_CROP_DPI", "300"))
+VERIFY_CROP_MARGIN_PTS = int(os.getenv("VERIFY_CROP_MARGIN_PTS", "36"))# padding around evidence bbox (PDF points)
+
 # Agent-mode human-review gate. When on (default), Agent runs stop after the
 # Brain merge and wait for human decisions before RFIs/final report/email go
 # out. AGENT_REVIEW_AUDIT_SAMPLE caps how many clean clusters get added to the