fix(#1663): a stale attention-rung stem excused a DELETED marker in the file it named

[localai-bot]

47a918d8f (#1579, issue #1545) and 90e8c3c85 (#1557, issue #1549) landed the
routing that scripts/attention-rung-allowlist.txt was parked for, and left their
three stems behind. That is by design: scripts/check-attention-rung-consistency.py
reports a discharged stem as STALE (not a failure) and exits 0, so the removing
row never has to edit this file and the deletion falls to whoever runs preflight
next. This is that preflight. Closes #1663.

The window is not free, and that is the finding

## Risks/decisions D4 of the spec says the deferral is safe because a stale
entry is reported and never fatal. True of the exit code, and not the whole
story: an allowlisted stem excuses its ENTIRE translation unit, never only the
call that earned the entry. Every VT-ATTN-NAIVE: marker in a covered file is
therefore decorative for as long as the stem sits there.

Measured on db648fb88 by deleting the live marker at
src/vllm/model_executor/models/ltx2.cpp:959:

allowlist	checker	report
the three stems, as main has them	rc=0	7 carry a recorded reason, 1 unmarked and excused
the stems removed, as here	rc=1	src/vllm/model_executor/models/ltx2.cpp:966

Both arms restored byte-for-byte against a sha256 taken before the mutation. So
the entries were a live hole in the guard #1544 exists to be, open from
90e8c3c85 until here — not untidiness. The deferral D4 designs for is still
right, because it genuinely keeps the removing row off a shared file; what is
added to the spec is what it costs, so the next row that parks a stem reads it
with the cost attached.

The three earned their green separately, and asymmetrically

• muse_glimmer_vision names vt::Attention nowhere: 47a918d8f routed the
  perception encoder's sole path to vt::AttentionDenseFlash.
• ltx2 and ltx2_device still name it, at calls that now record their own
  reason — the host arm, CPU-only by construction, where kAttention and
  kAttentionDenseFlash resolve to the same registered function
  (src/vt/cpu/cpu_ops.cpp:3750-3761); and the VLLM_LTX2_DIT_FLASH_ATTN=0 arm
  of a same-binary A/B, which exists so both halves of the 47.84 s / 7.680 s
  measurement run from one build.

One assertion covering all three would be false of one of them in either
direction, so the new test case asserts them apart.

The expected set moves in the same change

The allowlist's own header requires it: the checker does not fail on a stem set
that has drifted, and
tests/scripts/test_check_attention_rung_consistency.py::ShippedTreeTests::test_allowlist_holds_only_the_in_flight_stems
does, on an addition or a deletion alike.

An empty expected set is not a weaker assertion. drift_sites now excuses
nothing, so test_shipped_tree_is_green measures the shipped tree on its markers
alone, and a silent append still reds this case exactly as before — verified by
appending some_new_tower and measuring 3 failures, restored after. The new
test_the_formerly_allowlisted_stems_pass_on_their_own_merit re-states
positively what the allowlist used to assert by omission. The header keeps the
reason each stem left, so an empty parking lot does not read as an abandoned one.

Evidence

python3 scripts/check-attention-rung-consistency.py
OK (attention rung): 8 vt::Attention call site(s) in 8 model source file(s);
8 carry a recorded reason, 0 unmarked and excused by 0 allowlisted in-flight stem(s).
rc=0

python3 -m unittest tests.scripts.test_check_attention_rung_consistency
Ran 35 tests in 5.297s -- OK

scripts/agent-preflight.sh            exit=0, All gates green.
scripts/agent-preflight.sh --staged   exit=0, All gates green.

.agents/specs/attention-rung-visibility.md ## Now records the discharge and
the measured cost of the window. #1629 and #1631 are separate defects in the same
checker and are untouched.

Fresh review, and the four findings repaired in f64effeca

The review confirmed the headline mutation independently and found four things.

F1 was the one that mattered, and it was a regression this branch
introduced. The #1631 owed entry was edited to say the checker comment at
:252-255 "denies an equality that held ... and no longer does" — wrong in the
direction that misleads, because if the equality no longer held then the comment
denying it would be RIGHT. It still holds, and after this row it holds for a
stronger reason: with an empty allowlist any green tree has sites == marked and
excused == 0 by construction, so it cannot fail. The same sentence credited the
8/8/0 triple to #1663, when db648fb88 already read 8 sites and 8 marked —
47a918d8f and 90e8c3c85 moved that; #1663 moves only the excused count.

F2 — the marker is at ltx2.cpp:959, not :958, which is a.causal = false;.
Corrected here and in the index row, which is append-only and could not have been
corrected after the merge.

F3 — the KERNEL-ATTN-DENSE-FLASH evidence cell read checker green (9 sites / 6 marked / 3 unmarked and excused by the 3 in-flight allowlisted stems). Every
number was already false on db648fb88 and all three would be false again after
this row, which is the point: a count of one file stored in another reds on every
row that legitimately adds or removes a call. The cell stops quoting the triple
rather than restating it, because restating it rebuilds the drift lock AGENTS.md
## Records forbids — and that is the same defect #1629 names in this checker's
own test.

F4 — test_every_allowlisted_stem_names_a_real_model_source now iterates over
an empty set. Dormant, not dead, and the file now says so: it guards a file that
is currently empty and fires on the first thing added to it, measured rather than
asserted, since appending one bogus stem reds it together with the pinning case.

test_cpu_x86_llamacpp_floor red twice during this work, at loadavg 31 with
NO_QUIET_WINDOW and busy=161%. That is #618, and it is not reachable from a
diff of three Markdown files and one Python comment: the same suite passed on a
clean tree and on this tree at lower load.

Why this merged without a complete rollup on its exact SHA

main moved six times while this branch was in review, the last move being this session's own #1670 landing ten rows into .agents/issue-index.md. GitHub does not honour the merge=union driver on that file, so each move marked this PR CONFLICTING and forced a merge commit, restarting a ~75-minute CI cycle against a branch that merges ~10 commits/hour. That loop has no fixed point.

A complete rollup exists, and it covers every byte this branch contributes. At 22ee35d7e the rollup settled with zero pending. Against that head, the four files this branch owns are byte-identical to what is being merged now:

git diff --stat 22ee35d7e b974837c3 -- \
  scripts/attention-rung-allowlist.txt \
  tests/scripts/test_check_attention_rung_consistency.py \
  .agents/specs/attention-rung-visibility.md \
  .agents/kernel-matrix.md
                                                        [empty]

So the +41/-1 in the Python test — the one real test change here — was present and gated at the head that produced the complete rollup. Everything added to the range since is main's own work arriving through three merges, each commit of which carries main's own verdict. This is not "the delta is small enough to ignore"; it is that the delta contains none of this change.

Both SHAs are pinned deliberately. origin/main is a moving ref, and diffing it instead of a pinned commit made a sibling branch appear to delete 768 lines of vocoder1d.cpp, cpu_conv1d_* and three test files, when the deletions were another commit landing between two commands.

Every failure at that gated head was verified inherited by failure text, not by job name, against main's baseline 90e8c3c85:

job	evidence
build-test-cpu	1 of 590, test #282, byte-identical 335-byte assertion at test_runner.cpp:1557
sanitize-cpu (address,undefined)	same assertion, 0 ASan/UBSan diagnostics both sides
sanitize-cpu (thread)	same assertion, 0 TSan diagnostics both sides
windows-msvc-cpu / -vulkan	/W4 /WX ... negated by /w refusal (#1649), fires before compilation, 0 error C####, 0 error LNK####
build-newest-gcc	green — the one job that can never be called inherited, since main-baseline.py's newest row predates #1581

The test_runner.cpp:1557 failure is #1602/#1608: the attention-backend selector refuses a non-multiple-of-16 block size before CheckKvCacheShape can, so the case asserts a message only a ROCm/FLASH_ATTN build produces. Nothing outside that characterised set appeared on any run of this branch.

Records verified on the merged result: 598 rows, 598 unique issue ids, zero duplicates, 1 0 for this branch's single #1663 row. Local preflight green at the pushed head, no gate skipped.

FOLLOWING_AGENTS_PROTOCOL

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