My design note was half right, and the audit caught the other half. Keeping
engraved_spelling_chain physically separate from respell_chain was correct --
respell_chain is RespellPitch's LWW working state, read by its
concurrent-differing conflict detection, and folding transposes into it would
make a concurrent respell conflict with a transpose and move the canonical
bytes of every existing history. What that did NOT license was letting one
operation own the key.
RespellPitch mutates the same graph attachments and recorded nowhere on the
attachment chain, so a chain with a single writer was wrong both ways. Both
reproduced:
respell -> [tx: transpose] -> StrictInverse undo
Applied; pitch restored to C4; the UserChosen(C) attachment ERASED.
The respell was an operation, not part of the base, so the transpose's
chain had never seen it and its predecessor was absence.
[tx: transpose] -> respell -> StrictInverse undo
Applied; the newer UserChosen(D) authoring WIPED. The respell was
invisible to the chain, so it never registered as a superseding writer,
contradicting the catalog's rule that a later canonical writer supersedes
a strict undo.
And BestEffort could restore the pre-transpose pitch while leaving a spelling
authored against the transposed one attached to it.
Fix: every writer of the attachments records on the attachment chain
(record_engraved_spellings), and a pitch's value and its engraved spelling set
undo as one unit -- if either half is superseded, neither is restored.
StrictInverse already refuses on any supersession, so the coupling only bites
for BestEffort. Two physical chains, two responsibilities: respell_chain owns
the ledger spelling and the LWW verdict, engraved_spelling_chain owns the graph
attachments.
Recording is gated on graph presence, so base-free reduction is byte-unchanged
and the seeded corpus's canonical-base digest does not move.
Four tests, two mutations verified: removing the respell's record fails all
three undo tests; removing the coupling fails the best-effort one with the
pitch back at C4 and its spelling still at C-sharp. The fourth test locks
convergence -- both permutations of a concurrent respell/transpose reduce to
identical canonical bytes.
Spec: new req:opcat:spelling-set-chain. Batch 3 of the Pass-13 ledger reopens
(P13-S1, S2 open; S3 resolved here).
Also: PitchSpelling::transposed's doc said B-sharp 3 becomes F-double-sharp 3.
The code, spec, and tests all correctly produce F-double-sharp 4 -- B to F
carries the octave. Doc only.
Gate: fmt clean, clippy 0, 30 targets / 998 passed / 0 failed, docs 0 under
-D warnings, conformance 8/8, zero golden churn, canonical-base digest unmoved.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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