`BNode`'s `Cursor` branch stopped at `{.error.}` stubs. Everything structural
now works, so `-d:newIcBackend` no longer fails on the shape of the tree — the
remaining stubs (`sym`, `typ`, `info`) are the three that need the decoder's
symbol/type/line-info maps, which is the honest next boundary.
Two corrections to the seam, both found by looking at what actually reads a
`.bif`:
* it was pointed at `nifcursors`, the WRITER cursor over `PackedToken`s.
`bif.load` produces a `nifcore.TokenBuf` and `ast2nif` decodes it with a
`nifcore.Cursor`; that is the type the backend will get.
* the cost model said reading child `i` is O(size of children 0..<i). It is
O(i): a `TagLit` token stores the width of its whole subtree, so
`nifcore.skip` is one pointer add no matter how big the subtree is. Indexed
loops are still quadratic and still worth removing, but in the number of
children, not in tree size.
`kind` is the accessor the stub called pivotal, and the note on it was wrong in
a way that matters: a `.bif` carries its OWN tag pool, so a tag id means
nothing outside its file and the "build a tag-id -> TNodeKind table once" plan
cannot work. It memoizes per pool and drops the memo when the pool changes.
Since no call site executes any of this yet, `when isMainModule` walks real
`.bif` files and checks the vocabulary against itself and against an uncached
tag lookup. Over 70 files (`.s.bif`, `.t.bif`, `.iface.bif`) from the
testworkspace corpus: 2.05M nodes, 9.19M assertions, all passing. Both halves
of the harness were confirmed live by sabotage — `secondSon` returning child 2
trips it, and so does dropping the tag-pool memo invalidation, which is what
proves ids really do differ between files.
The default build is untouched: all 216 generated `.c` files still byte-
identical to the parent commit.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FMyRHByv7hhaQJ4Pa1bHbE
20b70c8b1e