fix(document-processors): correct cascade escalation metric + review nits

Address round-1 review on PR #914:
- Attribute the OCR hop in a fast->structured->ocr inline cascade to
  from_tier="structured" (not a second "fast" escalation), so
  astrolabe_document_escalation_total per-tier counts stay accurate.
- Add test_inline_fast_structured_ocr_cascade pinning that two-hop path and the
  metric attribution.
- Note in classify_from_text that its doc-level control ratio is over full_text
  (all pages), not the sampled subset classify_pdf uses.
- Clarify that corrupt_glyphs never lands in the suppressed-escalation counter.
- Dedupe the glyph-corrupt test string into tests/fixtures/glyph_corruption.py.
- Use pytest.approx for the control-char-ratio zero checks (SonarCloud S1244).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/test_doc_classifier.py

@@ -14,6 +14,7 @@ import pymupdf
 import pytest
 
 from nextcloud_mcp_server.document_processors import classifier as clf
+from tests.fixtures.glyph_corruption import GLYPH_CORRUPT_TEXT
 
 pytestmark = pytest.mark.unit
 
@@ -324,17 +325,17 @@ def test_scan_coverage_shorter_than_pages_aligns_without_crash():
 
 # --- glyph-corruption signal (broken /ToUnicode -> structured escalation) -----
 
-# pypdfium2-style leak: a uniform glyph/Caesar offset turns clean prose into
-# alphabetic-but-wrong tokens (normal spacing + token length => HIGH text_quality)
-# while digits/punctuation map to C0 control bytes. The control-char ratio is the
-# only signal that catches this; _text_quality scores it ~1.0.
-_GLYPH_CORRUPT = "WKH \x0f TXLFN \x10 EURZQ \x11 IRA MXPSV \x0f RYHU \x10 GRJ " * 6
+# A uniform glyph/Caesar offset turns clean prose into alphabetic-but-wrong tokens
+# (normal spacing + token length => HIGH text_quality) while digits/punctuation map
+# to C0 control bytes. The control-char ratio is the only signal that catches this;
+# _text_quality scores it ~1.0. Shared with the registry tiering tests.
+_GLYPH_CORRUPT = GLYPH_CORRUPT_TEXT
 
 
 def test_control_char_ratio_clean_is_zero():
-    assert clf._control_char_ratio("the quick brown fox") == 0.0
+    assert clf._control_char_ratio("the quick brown fox") == pytest.approx(0.0)
     # legitimate whitespace controls (tab/newline/CR/form-feed/vtab) don't count
-    assert clf._control_char_ratio("a\tb\nc\r\nd\f\ve") == 0.0
+    assert clf._control_char_ratio("a\tb\nc\r\nd\f\ve") == pytest.approx(0.0)
 
 
 def test_control_char_ratio_detects_glyph_leak():

tests/unit/test_registry_tiering.py

@@ -4,7 +4,7 @@ Covers: default fast-tier routing, the pymupdf rollback toggle, classification
 recording derived from the extraction, and OCR escalation (on/off).
 """
 
-from unittest.mock import MagicMock
+from unittest.mock import MagicMock, call
 
 import pytest
 
@@ -15,6 +15,7 @@ from nextcloud_mcp_server.document_processors.base import (
 )
 from nextcloud_mcp_server.document_processors.escalation import EscalationDecision
 from nextcloud_mcp_server.document_processors.registry import ProcessorRegistry
+from tests.fixtures.glyph_corruption import GLYPH_CORRUPT_TEXT
 
 pytestmark = pytest.mark.unit
 
@@ -250,10 +251,10 @@ async def test_no_ocr_escalation_when_disabled(monkeypatch):
 
 # --- glyph-corruption escalation + full-ladder parity ------------------------
 
-# A fast-tier text layer that looks like words (normal spacing/token lengths ->
-# HIGH text_quality) but leaks C0 control chars: the broken-/ToUnicode signature
-# the control-char ratio catches. Decodes to a pangram under a -3 shift.
-_GLYPH = "WKH \x0f TXLFN \x10 EURZQ \x11 IRA MXPSV \x0f RYHU \x10 GRJ " * 6
+# A fast-tier text layer that looks like words (HIGH text_quality) but leaks C0
+# control chars -- the broken-/ToUnicode signature the control-char ratio catches.
+# Shared with the classifier tests so the two can't diverge.
+_GLYPH = GLYPH_CORRUPT_TEXT
 
 
 async def test_glyph_corrupt_escalates_fast_to_structured(monkeypatch):
@@ -311,6 +312,27 @@ async def test_inline_empty_skips_structured_straight_to_ocr(monkeypatch):
     esc.assert_called_once_with("fast", "ocr", "empty_text")
 
 
+async def test_inline_fast_structured_ocr_cascade(monkeypatch):
+    # Full cascade: a junk-but-non-empty fast layer hops to structured, the
+    # structured re-extract is empty (a doc that was ALSO scanned), so it then
+    # hops to OCR. The second hop must be attributed from_tier="structured",
+    # NOT a second "fast" escalation.
+    monkeypatch.setattr(reg_mod, "get_settings", lambda: _Settings(ocr=True))
+    esc = MagicMock()
+    monkeypatch.setattr(reg_mod, "record_document_escalation", esc)
+    r = _registry(
+        (_Fake("fast", "fast", text="x" * 40), 20),  # quality ~0, non-empty
+        (_Fake("structured", "structured", text=""), 10),  # re-extract empty
+        (_Fake("ocr", "ocr", text="ocr recovered text"), 5),
+    )
+    res = await r.process(b"%PDF-1.7", "application/pdf")
+    assert res.processor == "ocr"
+    assert esc.call_args_list == [
+        call("fast", "structured", "low_confidence"),
+        call("structured", "ocr", "empty_text"),
+    ]
+
+
 def test_evaluate_escalation_glyph_corrupt_goes_structured(monkeypatch):
     # External path mirrors the inline path: glyph-corrupt -> structured, never OCR.
     monkeypatch.setattr(reg_mod, "record_document_classification", MagicMock())