[wojo]

Fixes #1539.

A disk state that its family refuses while it scatters is now forgotten after one recall, the way a file that fails
its own checks already is.

What changes

• One copy path. rows_read.one and the read-ahead branch of read called the family's scatter with a bare
  try. Both now go through one helper. A refusal goes to bad with the file being copied (a block's .blk, or the
  state's own .st), so that file is counted, logged and unlinked once, with every state that names it.
• What counts as a refusal. Words the family will not take (DiskWords, KeptWordsDiffer), or a size or range
  that does not fit its blank (SnapshotSize, BadKeptRange). They are one switch (refused), so a family's new
  refusal is one line. On main, Nemotron raises SnapshotSize, and Qwen3.5 and Flash Next raise KeptWordsDiffer and
  BadKeptRange, all from inside scatter. GLM's DiskWords arrives with GLM-5.3-Flash on CUDA keeps conversation states on disk, every rank's part (--learn-conversations) #1411.
• Other errors pass through as before. A failing link or memory keeps the state and its read.
• Reads ahead. bad now drops the read ahead of every state it forgets (Prefetch.forget), whoever called it.
  Before, a taken read stayed listed until a sweep, and a state of the same name written later could have joined it
  again, refused words and all.

Tests

rows_refusal_test.zig recalls a state with the fault on a shared head block (both states go), on the state's own
file (only it goes) and with a transient error (kept). It does this synchronously and with both states read ahead,
and checks the counts, the states, the files and the reads of both. The Fake family gains a scatters fault (after
n copies, every one fails with a given error).

• With the fix reverted, both tests fail at rows_refusal_test.zig:126 (expected 1, found 0: nothing counted, the
  state kept).
• With KeptWordsDiffer or BadKeptRange removed from refused, both fail at the same line.
• With only Prefetch.forget removed from bad, the read-ahead test fails at :137 (expected 2, found 0: the
  forgotten states' reads never freed).

Host (Zig 0.17.0, an M4 Mac), on the branch's head: test-rows-host, test-rows-prefetch-host,
test-learn-recovery, test-cuda-host, test-snapshot-index-host, test-lane-api-host and test-golden pass
(286/286 steps). zig fmt --check and git diff --check are clean, and lean_check.py reports 426 on main and on the
branch. No GPU run: on main a scatter refusal follows only a writer bug, and these tests drive it through the Fake
family.

By Robert Wojciechowski (wojo on GitHub, @rwojo on X)

[ashhart]

Thank you @wojo. This is in TensorFold 1.2.0, released today: https://github.com/ashhart/TensorFold/releases/tag/v1.2.0

It landed with your commits under your own name, so you're listed as a TensorFold contributor, and it's credited to you in the release notes and the changelog.