docs(Tokenizer): define opening-anchor contract

[cixzhang]

Why

PowerSearch’s readable editor placement needs a stable opening-control identity from Tokenizer without publishing DOM refs, pointer coordinates, or width tuning as consumer API.

What

• Promotes the Tokenizer component contract to authority: current with Cindy’s recorded approval.
• Records one component DEC for the package-internal outer-field/opening-control descriptor, width-first full-width versus narrower placement, modality-neutral anchoring, one read batch per open, hidden commit, next-frame show, and no continuous tracking.
• Keeps Tokenizer’s public API and existing suggestion-menu sizing unchanged.
• Requires real-Chromium open-state evidence when the runtime implementation ships.

#5804 remains dependent draft evidence and owns its separate PowerSearch editor-width policy. Implementation and focused runtime verification remain pending.

Risk

Documentation only. No runtime, public API, consumer docs, stories, or Changeset changes.

Testing

• pnpm check:knowledge
• pnpm check:repo
• pnpm exec prettier --check packages/core/src/Tokenizer/Tokenizer.spec.md
• pnpm exec vitest run scripts/check-knowledge.test.mjs (60 tests)
• git diff --check

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Project	Deployment	Actions	Updated
astryx	Ready	Preview	Sep 1, 2026 5:03am UTC

[cixzhang]

/approve-spec 8ce38fc

[cixzhang]

/approve-spec 8ce38fc