Portable emit targets (ts/go/rust) have no incremental `edit` — full re-parse only

[johnsoncodehk]

The target-agnostic emitter (#6, #56) emits portable parsers in TypeScript, Go, and Rust, but they are full-parse only — they expose tokenize(src) + parse(tokens) and have no incremental re-parse. Incremental edit exists only in the JS paths:

Path	Incremental
createParser() interpreter	✅ .edit(...)
jsTarget (optimized JS emit)	✅ exported parseEdited (PR #38)
portable tsTarget / goTarget / rustTarget	❌ full parse(tokenize(src)) only

Why

The incremental machinery — watermarked memo carry, subtree reuse (adoptPath), and the maxPos watermark — lives in the optimized path (src/emit-parser.ts / src/gen-parser.ts), shipped as parseEdited in PR #38 and gated ≡ fresh (1.4–5.6×). The portable emitter (src/emit-portable.ts's buildIR) renders a different, simpler parser: a clean backtracking recursive-descent + Pratt core with no memo / no incremental infrastructure. So nothing in the portable IR or the target-*.ts renderers can carry a prior parse forward.

What it would take

• Lift the memo-carry + watermark + subtree-reuse model into the language-agnostic IR layer so each Target can render it.
• Per-target incremental state: ts via module globals; go/rust need incremental arena reclamation (reusing surviving subtrees without leaking the flat nodes/kids slices).
• Extend test/portable-targets.ts to assert edit ≡ fresh for the portable targets, mirroring the existing JS incremental gate.

Substantial — not a single-construct change. Tracking it as a known boundary of the portable emitter; the JS interpreter / jsTarget remain the path for incremental use until then.