diff --git a/CMakeLists.txt b/CMakeLists.txt
index 610142905..ce51ba4de 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -323,6 +323,13 @@ add_python_test(tests_referenced_self ${CMAKE_SOURCE_DIR}/tools/ci/tests_referen
 # Registered through add_python_test (engine#1864), so they run THROUGH the interpreter: my first version used the raw
 # `${Python3_EXECUTABLE}` form above the find_package and the repository's own ordering guard caught it by name --
 # tools/mtp_head_ref.py is the one of the five without an exec bit, and it became BAD_COMMAND under ctest.
+# engine#1962: the narrowing-body enumeration, as a ratchet. The corpus is a submodule, so the check
+# skips (rc 77) where third_party/llama.cpp is not checked out; the baseline file is in the engine tree,
+# so the recorded set is reviewable everywhere.
+add_python_test(tool_selftest_hrx_f16_narrowing ${CMAKE_SOURCE_DIR}/tools/ci/hrx_f16_narrowing.py --self-test)
+add_test(NAME hrx_f16_narrowing_check COMMAND ${Python3_EXECUTABLE}
+         ${CMAKE_SOURCE_DIR}/tools/ci/hrx_f16_narrowing.py --check --root ${CMAKE_SOURCE_DIR})
+set_tests_properties(hrx_f16_narrowing_check PROPERTIES SKIP_RETURN_CODE 77)
 add_python_test(tool_selftest_batched_repeat ${CMAKE_SOURCE_DIR}/tools/batched_repeat.py --selftest)
 add_python_test(tool_selftest_logprob_agree ${CMAKE_SOURCE_DIR}/tools/logprob_agree.py --selftest)
 add_python_test(tool_selftest_mtp_head_ref ${CMAKE_SOURCE_DIR}/tools/mtp_head_ref.py --selftest)
diff --git a/tools/ci/hrx_f16_narrowing.py b/tools/ci/hrx_f16_narrowing.py
new file mode 100755
index 000000000..4d4034a0f
--- /dev/null
+++ b/tools/ci/hrx_f16_narrowing.py
@@ -0,0 +1,185 @@
+#!/usr/bin/env python3
+# Copyright 2026 bong-water-water-bong
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""hrx_f16_narrowing.py -- keep the engine#1962 enumeration from drifting while it is being finished.
+
+engine#1962 is "a dense MUL_MAT returns NaN or wrong values when an activation exceeds the f16 range".
+Its repairs land on the *producers* (a plan records a 2^-6 prescale and the consumer scales back), and
+the question the issue still holds open is: **which of the narrowing consumers are protected**. That
+cannot be answered by reading the consumers -- the guard is not in them -- so the enumeration is only
+worth anything if it cannot silently change underneath the person answering it.
+
+This is the ratchet:
+
+  * every .loom body that narrows f32 to f16 (`f32 to f16` or `truncf`) is listed in
+    tools/ci/hrx_f16_narrowing.txt, and a body that appears without a line, or a line whose body is gone,
+    fails the check -- the two arms a ratchet needs (a list that can only grow cannot see a rename,
+    engine#1728's lesson);
+  * the producer-side guard markers (`scale_log2`, `prescale`) are counted per body and reported, but
+    **not** asserted as zero: moving the guard from the producer to the consumer is the issue's own
+    option 2, and when that happens the count must change and the baseline must be updated deliberately.
+
+The corpus is a submodule, so the check skips (rc 77) without third_party/llama.cpp checked out -- the
+data file is in the engine tree, so the recorded set is visible in review even where the check cannot run.
+
+usage: hrx_f16_narrowing.py --check [--root .]     rc 1 on drift, rc 77 without the corpus
+       hrx_f16_narrowing.py --self-test            fixtures only, no corpus
+       hrx_f16_narrowing.py --write                rewrite the baseline from the corpus
+"""
+import argparse
+import pathlib
+import sys
+
+CORPUS = pathlib.Path("third_party/llama.cpp/ggml/src/ggml-hrx/kernel-corpus/kernels")
+BASELINE = pathlib.Path("tools/ci/hrx_f16_narrowing.txt")
+NARROW = ("f32 to f16", "truncf")
+GUARD = ("scale_log2", "prescale")
+
+
+def baseline_paths(text):
+    return {line.strip() for line in text.splitlines()
+            if line.strip() and not line.lstrip().startswith("#")}
+
+
+def narrowing_bodies(corpus):
+    """Every .loom under the corpus that narrows f32 to f16, as corpus-relative POSIX paths."""
+    found = set()
+    for path in corpus.rglob("*.loom"):
+        body = path.read_text(encoding="utf-8", errors="replace")
+        if any(marker in body for marker in NARROW):
+            found.add(path.relative_to(corpus).as_posix())
+    return found
+
+
+def guarded(bodies, corpus):
+    """Bodies that also carry a producer-side guard marker -- reported, never asserted."""
+    out = set()
+    for rel in bodies:
+        body = (corpus / rel).read_text(encoding="utf-8", errors="replace")
+        if any(marker in body for marker in GUARD):
+            out.add(rel)
+    return out
+
+
+def drift(baseline, found):
+    return sorted(found - baseline), sorted(baseline - found)
+
+
+def check(root):
+    corpus = root / CORPUS
+    if not corpus.is_dir() or not any(corpus.rglob("*.loom")):
+        print(f"skip: no .loom corpus at {CORPUS} (check out third_party/llama.cpp)", file=sys.stderr)
+        return 77
+    base_text = (root / BASELINE).read_text(encoding="utf-8")
+    baseline = baseline_paths(base_text)
+    found = narrowing_bodies(corpus)
+    new, stale = drift(baseline, found)
+    guard = guarded(found, corpus)
+    for rel in new:
+        print(f"hrx_f16_narrowing: NEW narrowing body {rel} -- it narrows an f32 value to f16 and the "
+              f"baseline does not name it; add the line and say what feeds it (engine#1962)")
+    for rel in stale:
+        print(f"hrx_f16_narrowing: {rel} is in the baseline but no longer narrows -- drop the line, the "
+              f"list should shrink")
+    if new or stale:
+        print(f"hrx_f16_narrowing: FAIL ({len(new)} new, {len(stale)} stale of {len(baseline)})")
+        return 1
+    print(f"hrx_f16_narrowing: {len(baseline)} narrowing body(ies), none new, none stale; "
+          f"{len(guard)} of them carry a guard marker" +
+          (f" ({', '.join(sorted(guard))})" if guard else " (the guard sits on the producer, engine#1962)"))
+    return 0
+
+
+def write(root):
+    corpus = root / CORPUS
+    if not corpus.is_dir():
+        print(f"skip: no .loom corpus at {CORPUS}", file=sys.stderr)
+        return 77
+    head = "".join(line for line in (root / BASELINE).read_text(encoding="utf-8").splitlines(True)
+                   if line.lstrip().startswith("#"))
+    bodies = sorted(narrowing_bodies(corpus))
+    (root / BASELINE).write_text(head + "\n".join(bodies) + "\n", encoding="utf-8")
+    print(f"hrx_f16_narrowing: wrote {len(bodies)} body(ies) to {BASELINE}")
+    return 0
+
+
+def self_test():
+    import tempfile
+    failures = 0
+
+    def check_that(ok, what):
+        nonlocal failures
+        print(("ok   " if ok else "FAIL ") + what)
+        if not ok:
+            failures += 1
+
+    with tempfile.TemporaryDirectory() as tmp:
+        root = pathlib.Path(tmp)
+        corpus = root / CORPUS
+        corpus.mkdir(parents=True)
+        (root / BASELINE).parent.mkdir(parents=True, exist_ok=True)
+        (corpus / "a.loom").write_text("  %x = scalar.fptrunc %y : f32 to f16\n")
+        (corpus / "b.loom").write_text("  %x = scalar.constant 1.0 : f32\n")
+        (root / BASELINE).write_text("# comment\n# another\na.loom\n")
+        check_that(not drift(baseline_paths((root / BASELINE).read_text()), narrowing_bodies(corpus))[0],
+                   "an unchanged corpus has no drift")
+        (corpus / "c.loom").write_text("  %z = scalar.fptrunc %w : f32 to f16\n")
+        new, stale = drift(baseline_paths((root / BASELINE).read_text()), narrowing_bodies(corpus))
+        check_that(new == ["c.loom"] and not stale, "a new narrowing body is drift, and only it")
+        (corpus / "c.loom").write_text("  %z = scalar.constant 0.0 : f32\n")
+        (corpus / "a.loom").rename(corpus / "renamed.loom")
+        new, stale = drift(baseline_paths((root / BASELINE).read_text()), narrowing_bodies(corpus))
+        check_that(stale == ["a.loom"],
+                   "a rename leaves a stale baseline line (the engine#1728 lesson)")
+        (corpus / "renamed.loom").write_text("  %x = scalar.fptrunc %y : f32 to f16  # scale_log2\n")
+        check_that(guarded({"renamed.loom"}, corpus) == {"renamed.loom"},
+                   "a guard marker is reported, not denied")
+        (corpus / "renamed.loom").write_text("  %x = scalar.fptrunc %y : f32 to f16\n")
+        check_that(guarded({"renamed.loom"}, corpus) == set(),
+                   "and an unguarded body reports no guard")
+        # The comments in the baseline are not bodies.
+        (root / BASELINE).write_text("# f32 to f16 is the marker\nrenamed.loom\n")
+        check_that(baseline_paths((root / BASELINE).read_text()) == {"renamed.loom"},
+                   "a '#' line in the baseline is not a path (the trailing-comment trap)")
+        # A missing corpus is a skip, not a pass.
+        empty = root / "empty"
+        empty.mkdir()
+        check_that(check(empty) == 77, "a missing corpus returns 77, not 0")
+
+    print(f"hrx_f16_narrowing self-test: {'ok' if not failures else f'{failures} failure(s)'}")
+    return 1 if failures else 0
+
+
+def main():
+    ap = argparse.ArgumentParser(description=__doc__.splitlines()[0])
+    ap.add_argument("--check", action="store_true")
+    ap.add_argument("--write", action="store_true")
+    ap.add_argument("--self-test", action="store_true")
+    ap.add_argument("--root", default=".")
+    args = ap.parse_args()
+    root = pathlib.Path(args.root).resolve()
+    if args.self_test:
+        return self_test()
+    if args.write:
+        return write(root)
+    if args.check:
+        return check(root)
+    ap.print_help()
+    return 2
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/tools/ci/hrx_f16_narrowing.txt b/tools/ci/hrx_f16_narrowing.txt
new file mode 100644
index 000000000..b7e67e613
--- /dev/null
+++ b/tools/ci/hrx_f16_narrowing.txt
@@ -0,0 +1,48 @@
+# Copyright 2026 bong-water-water-bong
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# Targets whose add_test() names them and which CI never builds (engine#1595).
+#
+# engine#1962: the .loom bodies that narrow an f32 value to f16, at llama.cpp pin 7a1f2b81c.
+# Paths are relative to third_party/llama.cpp/ggml/src/ggml-hrx/kernel-corpus/kernels. This is a
+# RATCHET, not a list of bugs: a body here may narrow a bounded value (a scale, a weight) and be
+# perfectly correct. What the list buys is that a NEW narrowing body cannot appear without someone
+# writing it down and saying what feeds it -- and that is the open question on engine#1962: which of
+# these are protected by a producer-side prescale cannot be answered by reading them.
+loom-libs/motifs/mul_mat_id_f16_f16_wmma_core.loom
+loom-libs/motifs/mul_mat_id_q4k_f16_wmma_projection.loom
+loom-libs/motifs/mul_mat_id_q5k_f16_wmma_projection.loom
+loom-libs/motifs/q4_k_f16.loom
+loom-libs/motifs/quantize_q8_1_x4.loom
+loom-libs/motifs/unary_f32_apply.loom
+loom-libs/ops/flash_attention_decode_split_f32_f16_wmma.loom
+loom-libs/ops/flash_attention_f32_f16_wmma.loom
+loom-libs/ops/gated_delta_net_f32_wmma.loom
+loom-libs/ops/llm_attention_v_matmul_set_rows_decode_f32_f32.loom
+loom-libs/ops/mul_mat_swiglu_symmetric_i4_wmma.loom
+loom-libs/ops/mul_mat_symmetric_i8_wmma.loom
+loom-libs/ops/set_rows.loom
+loom-libs/ops/small_rows_f32.loom
+qwen_moe/ggml/quantize_q8_1_x4.loom
+qwen_moe/qwen3_moe/attention_prepare_quantized.loom
+qwen_moe/qwen3_moe/dense_linear_quantized_f16_wmma.loom
+qwen_moe/qwen3_moe/flash_attention_decode_f32_f16_wmma.loom
+qwen_moe/qwen3_moe/flash_attention_decode_q128_f32_f16_wmma.loom
+qwen_moe/qwen3_moe/flash_attention_decode_split_f32_f16_wmma.loom
+qwen_moe/qwen3_moe/flash_attention_decode_split_next_q8_test.loom
+qwen_moe/qwen3_moe/flash_attention_f32_f16_wmma.loom
+qwen_moe/qwen3_moe/routed_down_weighted_reduce_next_rmsnorm_q8_1_x4.loom
+qwen_moe/qwen3_moe/routed_gate_up_swiglu_q4k.loom
+qwen_moe/qwen3_moe/routed_linear_q4k_f16_wmma.loom
diff --git a/tools/copyright.py b/tools/copyright.py
index 840a92fa9..caf90f353 100644
--- a/tools/copyright.py
+++ b/tools/copyright.py
@@ -46,6 +46,7 @@
       "unreferenced_tests.txt",
       # engine#2018: the third test-registration baseline, same shape and the same reason -- data, `.txt` has no style.
       "unreferenced_py_tests.txt",
+            "hrx_f16_narrowing.txt",
       "21serial-console", "90onboard-limits", "Dockerfile", "*.Dockerfile",
       # cycle 17: Puppy's switch that skips its first-run Quick Setup is an empty marker file whose only content
       # is this notice - Puppy tests for its existence, so a comment is free