feat(tools): a re-measurable CID-glyph-share instrument for K2

Order 20260904T172353Z-6290714297-from-.claude. Bilag 9.1's 95.1 % CID
share (docs/2026-09-04-k3-arm-c.md) was found ad hoc, with no committed
script -- the same gap this repo's own fidelity instrument criticizes in
Arm A's uncommitted docx/xlsx figures. okf_cid_measure.py runs the exact
extract_text call the door makes and reports per-document CID share and
4+-letter word count, denominator stated for files it cannot measure.
Red-first: tests/test_cid_measure.py pins measure() against fixture text
of known composition before the implementation existed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_cid_measure.py

@@ -0,0 +1,50 @@
+"""The CID-share instrument: order 20260904T172353Z-6290714297-from-.claude.
+
+Measures how much of a document's extracted text is undecoded `(cid:N)` glyph
+codes -- the failure mode `docs/2026-09-04-k3-arm-c.md` found on Bilag 9.1
+(95.1 %, 98 alphabetic words of four or more letters survive). This instrument
+answers whether that document is alone or whether the corpus has more of them.
+
+The negative control matters here as much as the positive one: an instrument
+that reports a nonzero CID share on text that has none would inflate every
+number it ever produces, the same reason `test_fidelity.py` pins its own
+negative control.
+"""
+
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "tools"))
+
+import okf_cid_measure  # noqa: E402
+
+
+def test_known_cid_fraction() -> None:
+    text = "abcd efgh " + "(cid:12)" * 2
+    result = okf_cid_measure.measure(text)
+    assert result.total_chars == len(text) == 26
+    assert result.cid_chars == len("(cid:12)") * 2 == 16
+    assert result.word_count == 2  # "abcd", "efgh" -- "cid" itself is 3 letters
+    assert abs(result.pct - (16 / 26 * 100)) < 1e-9
+
+
+def test_no_cid_is_zero_with_nonzero_total() -> None:
+    result = okf_cid_measure.measure("plain readable text with no cid codes at all")
+    assert result.total_chars > 0
+    assert result.cid_chars == 0
+    assert result.pct == 0.0
+
+
+def test_all_cid_is_full_share_and_zero_words() -> None:
+    result = okf_cid_measure.measure("(cid:1)(cid:2)(cid:3)")
+    assert result.pct == 100.0
+    assert result.word_count == 0
+
+
+def test_empty_text_reports_zero_percent_not_a_crash() -> None:
+    result = okf_cid_measure.measure("")
+    assert result.total_chars == 0
+    assert result.cid_chars == 0
+    assert result.pct == 0.0