P4: scope cleanup — de-scope experimental surface, emit @glyph (Stage 6)

[phenomenon0]

Stage 6 — P4 scope cleanup

Branches off main. Go-only. No public APIs removed — this is comments/docs plus the header-spelling switch (a one-token change with parser back-compat preserved).

Experimental / de-scoped (code kept, marked in comments)

Each carries a "not integrated into the core Parse/Emit path; experimental, may change" note:

• Decimal128 (decimal128.go) — standalone, no GType, unreferenced by parse.go/emit.go/types.go/token.go. Known rough edges noted as consequences of it not being wired in.
• EmitV2 / EmitV2Patch (parse_header.go) — emit-only; there is no ParseV2Document, so output can't be round-tripped through a single v2 decoder.
• EncodeDictFrame (streaming.go) — emit-only; no DecodeDictFrame, no round-trip test. Per the roadmap's "add DecodeDictFrame OR mark experimental", I took the de-scope route.

Deprecated / experimental zero-caller emitters

Confirmed no production callers via grep before annotating:

• EmitTokenAware (token_aware.go)
• CanonicalHash (emit.go) — points users to FingerprintLoose (the cross-language-stable SHA-256 fingerprint) instead.

Two supported emitter layers (documentation)

doc.go now documents the collapse to two supported layers — Loose (CanonicalizeLoose, LLM-facing) and Typed (Emit, schema-bound) — and lists the secondary/experimental emitters as not part of that surface. Public APIs are untouched.

Header spelling (maintainer decision)

EmitHeader now emits the full @glyph spelling; ParseHeader still accepts both @glyph and the legacy @lyph. Updated the three emit-output assertions in v2_test.go; parser-input tests that feed @lyph are left as-is (both spellings still parse).

Notes

• No README/feature-list edits were needed — none of these symbols were ever advertised as features (verified by grep across all READMEs + docs/).
• Headers are not in the cross-impl/parity gate (only CanonicalizeLoose is), so the spelling change does not affect parity.
• JS/Py emitters still emit @lyph (both parsers accept both spellings, so interop is unaffected); aligning their emit spelling is a small recommended follow-up outside this Go-scoped branch.

Verification

ulimit -v 6000000; go test -C go ./glyph/ -skip 'Industrial|Cliff|Perf|Savings|Benchmark' -count=1 → green. go/stream tests green. go vet + go build ./... clean.

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