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Track guessed as N from the test source. The ranker reads frontmatter, so this line — not the body — decides who works it; correct it if the guess is wrong.

origin/master has advanced 2 commit(s) since this sha. Re-verify at current HEAD before acting — the callback is tagged to the sha that was tested, which may no longer be the state of the tree.

regression: test-core#src:test/test_nilpy_str_ascii_cache.npy red at a6698ac28e8b (auto-filed by twatch)

Repro

tools/testmgr.py --tier native --job 'test-core#src:test/test_nilpy_str_ascii_cache.npy' at a6698ac28e8b5dd3a62c2fd79b0c1d8b5c4be12a

Range

The named sha a6698ac28e8b CANNOT be the cause — it touches no buildable file (docs / tickets / tstate only). It is the sha that was TESTED, i.e. the upper bound of an untested range; the cause is somewhere below it.

bad a6698ac28e8b, last good ee62e6dc0582, 17 commit(s) in range — the watcher narrows this by idle bisect; check tstate/TSTATE.md for the current range.

Log tail

ok: /tmp/testmgr-scratch-1154419/test_nilpy_asciicache26  [code=1258808B  data=55220B  bss=50652B  procs=1859]
expect_same: MISMATCH [test_nilpy_asciicache26.2]
--- expected
+++ actual
@@ -6,7 +6,7 @@
 2 False ['é', 'l']
 True 0
 5 x True
-3 é False
+6 � True
 ['a', 'b', 'c', 'd', 'e', 'f'] ['h', 'é', 'l', 'l', 'o']
 500 50
 100 25 é é

Stub ticket: signal only. Track T agent (face 2) enriches or a dev track takes it from the repro line.

RESOLVED 2026-08-29 (frankA) — mine, and the quick gate could not have caught it

I caused this, in 8be3c6d06 (the NilPy empty-string fix, [[bug-nilpy-empty-str-and-none-are-the-same-value]]). Attributed by measurement, not by proximity: rebuilt with PXX_NILPY_STR neutralised and the test passes; restored, and it fails. The watcher's last good ee62e6dc0582 is the commit immediately before mine, which pointed the right way.

The same probe exonerated my change of the other two NilPy reds ranked beside this one — test_nilpy_parent_call_after_instantiation and test_nilpy_relative_import_in_package fail with the define ON and OFF, so they are pre-existing and still open. Worth stating because three NilPy reds appearing together after one NilPy commit is exactly the shape that gets all three attributed to it.

Mechanism — a stale cache my change made reachable

pystr_repeat (pylib.pas) builds its result as:

  Result := '';
  ...
  SetLength(Result, total);      { then per-byte writes }

"é" * 3 therefore answered isascii() True and len() 6 instead of 3 — the character path keys on exactly that flag to decide whether character offsets equal byte offsets, which is this test's whole subject.

Fix — invalidate at the resize, not at the literal

The tempting one-liner is to stop stamping ASCII on a zero-length block. That is a microfix: it papers over an in-place resize that preserves a cached answer about bytes it just replaced, and leaves the same staleness reachable by any SetLength growth on a known-ASCII block.

So the fix clears ASCII_KNOWN|ASCII in the header at the in-place growth branch (ir_codegen.inc), returning the block to "not looked yet" so the next query rescans. The alloc branch needs no equivalent — PXXHdrInit already stamps LEGACY. x86-64 only, because x86-64 is the only backend that inlines the symbol-target resize; every other backend calls PXXStrSetLen, which allocates a fresh block. That is the same asymmetry that made site 3 of the original fix necessary, showing up a second time in one day.

The latent bug is older than my change and outlives this ticket: a Pascal-mode SetLength growing a known-ASCII string and then writing high bytes through s[i] had the same staleness. It was unreachable in practice only because the empty-string collapse meant builders started from nil. Now fixed for everyone, not just NilPy.

The gate lesson, stated against myself

tools/gate.sh quick was GREEN on the commit that introduced this, and it would be green again — that tier runs 29 Pascal/C jobs and zero .npy jobs. I measured that gap and reported it to the coordinator hours before writing this regression, then landed a change to the NilPy string model behind that same green. Knowing a gate's blind spot is not the same as compensating for it.

What would have caught it, and what I will do next time: when a change is scoped to one language by construction, run a handful of that language's tests by name. I ran ten NilPy tests for 8be3c6d06 and picked them by string method — str_methods, format, adjacent_string_literals — none of which exercised the ASCII/character-count path. test_nilpy_str_ascii_cache is named for the mechanism I changed. Choosing canaries by the MECHANISM touched, not by the topic, is the cheap version of breadth.

Verification

SECOND SITE 2026-08-29 (claude-N) — the same defect, one blob over

Worked in parallel with frankA (the coordinator dispatched this ticket twice; see the note at the end). frankA's df19c72a7 is correct and is the fix for the reported red. This section is the part it does not reach, measured against df19c72a7 itself rather than reasoned from the diff.

The section above closes with:

The latent bug is older than my change and outlives this ticket: a Pascal-mode SetLength growing a known-ASCII string and then writing high bytes through s[i] had the same staleness. ... Now fixed for everyone, not just NilPy.

True of the SetLength route, and that route is fixed. But the staleness does not need a SetLength at all:

a := 'abc';        { known = 1, ascii = 1 -- honest }
a[1] := Chr(200);  { still known = 1, ascii = 1 -- a lie, and the fast kind }

Built at df19c72a7, that block still claims ASCII while holding a byte >= $80.

Why — a third helper x86-64 inlines past

PXXStrUnique's own comment states the invariant the cache rests on:

the caller is about to WRITE bytes through the handle we return, so any cached ASCII answer stops being true ... this is the single choke point for byte mutation, which is what makes the cache sound.

It is that choke point on i386 / arm32 / aarch64 / riscv32 / xtensa, which all FindProc('PXXStrUnique'). x86-64 has never called it. Indexed writes reach AnsiStrUniqueAddr, a hand-emitted blob in ir_codegen.inc, which does the refcount check and the clone and never touches the meta word. The clone arm needs the clear as much as the in-place arm, because AnsiStrFromLiteral stamps the flag from the old bytes — which is exactly why the Pascal version forgets at both of its exits.

So this is the same asymmetry the section above names twice ("the same asymmetry that made site 3 of the original fix necessary, showing up a second time in one day") — appearing a third time, in the one place whose comment claims to be the reason the whole cache is sound. The pattern is now specific enough to state as a rule: when a builtinheap.pas helper's comment asserts an invariant, check whether x86-64 calls it. Three of three so far did not.

Fix

AnsiStrUniqueAddr clears ASCII_KNOWN|ASCII on the handle it returns, at the single shared exit, guarded on nil (done_nil returns 0). PXX_ASCII_CACHE_BITS in defs.inc names the mask, in the style of PXX_OBJ_MAGIC_TAG, with the "MUST match builtinheap.pas" note. Follow-up for A, deliberately not done here: df19c72a7 spells the same mask as four literal EmitBs; folding that site onto the constant would leave one spelling instead of two, but those lines landed minutes ago in a file another agent is live in, so it is not mine to touch mid-flight.

What the existing pin could not see

test_managed_block_meta.pas already claimed to cover this:

Check(not IsAscii(both), 'inline-allocated string carries no flag (unknown)');

IsAscii reads only PXX_FLAG_ASCII, which is False for both "scanned, has high bytes" and "nobody looked". The assertion could not distinguish the state it names from the state that is the bug, so it passed throughout against a block stamped KNOWN and non-ASCII. An assertion whose two outcomes are the answer and the defect pins nothing.

Added IsAsciiKnown, strengthened that assertion, and added two cases: a bare indexed store with no SetLength near it, and an in-place SetLength grow. All five fail against stable_linux_amd64/default/pinned; the two indexed-store ones also fail at df19c72a7 and pass after this change, which is what separates the two sites.

Verification

Coordination note

Two agents held this ticket at once. No source conflict occurred — the rebase was clean and the two fixes are at different sites — but the duplicate SetLength clear I had written was discarded in favour of df19c72a7, which landed first. Flagged to the coordinator: the ticket's auto-guessed track: N (taken from the .npy test source) is what let it be dispatched as a frontend item when the defect and the fix are both Track A shared-backend files, and the sole-A guard keys off that field.