feat(core): ensureHfIds node-id pass + shared hf- mint helper (R1)

[vanceingalls]

What

Adds ensureHfIds(html: string): string in packages/core/src/parsers/hfIds.ts. Single DOM pass (via linkedom) that mints a data-hf-id attribute on every eligible element before the caller sees the markup.

Id derivation: FNV-1a 32-bit hash of tagName | sorted-attrs(\x00/\x01 separated) | ownText, last 4 chars of base-36, hf- prefix. Collision resolution appends a sibling counter and re-hashes. Preserves existing ids (elements with data-hf-id already set are skipped). Excludes non-visual tags: script, style, template, meta, link, noscript, base.

Fragment handling: detects bare HTML fragments (no <!doctype / <html) and wraps in a full document shell before parsing, then returns body.innerHTML — matching the pattern used by parseSourceDocument in sourceMutation.

Why

Counter-based ids (element-0, element-1, …) are positional. Inserting a new layer at position 0 shifts every id below it. The R1 milestone requires content-based, stable ids so that targeting operations (split, patch, probe) stay valid across re-parses and element insertions. T2 spec (stableIds.test.ts) defines the contract: same content → same id, adding a sibling doesn't change other ids, format matches /^hf-[a-z0-9]{4}$/.

How

• toHfId(hash) — slice(-4) of hash.toString(36) for better distribution across the suffix space
• data-hf-id is excluded from the hash input (prevents circular dependency on the attribute being set)
• Already-assigned ids tracked in a Set; duplicates get a counter suffix before re-hashing
• Fragment detection: /<!doctype|<html[\s>]/i.test(html) — if bare, wrap→parse→body.innerHTML

Test plan

• T2 spec: packages/core/src/parsers/stableIds.test.ts — 7 tests pass (3 were .fails stubs targeting R1; 4 were pre-existing baselines that must not regress)
• No changes to existing htmlParser tests needed at this layer (wiring is PR feat(core): clip-model hf- ids minted at parse, emitted as data-hf-id (R1) #1270)

[vanceingalls]

• feat(core): sourceMutation data-hf-id targeting (R1, T7) #1272
• feat(studio): sourcePatcher data-hf-id targeting (R1, T3) #1271
• feat(core): clip-model hf- ids minted at parse, emitted as data-hf-id (R1) #1270
• feat(core): ensureHfIds node-id pass + shared hf- mint helper (R1) #1269 👈 (View in Graphite)
• main

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