#90 residual: records separable only through broken-typed fields collide → order-dependent counter; hash couples to typeToString text

Follow-up to #90 (PR #140), from the PR review. Low severity — the primary #90 goal (no churn across compiler versions / unrelated edits) holds for the general case and is verified byte-identical on TS 5.9 → 6.0.3.

## Residual 1 — under-discrimination of broken-typed fields
`structuralSig` normalizes every `unknown`/`any`/`opaque`/`review` field to the same token, so two DISTINCT records separable only through broken-typed fields hash identically and fall back to an order-dependent counter (`…2`) — a narrow slice of the churn #90 targets.

- Real case: base-ui `menuStoreV1x8ec` / `…2` (differ only in `rootMenuStore…` vs `triggerMenuStore…`, both `→ string`).
- The PR #140 refinement (base + `t.text` in the sig) fixed base-ui but **regressed blend 0 → 2 counters** (`selectMenuGroupType2`, `selectMenuItemType2`), which are `structuralSig`-EQUAL entries (sort can't stabilize equal keys). So the churn class moved rather than disappeared.

## Residual 2 — hash couples to `typeToString`
The `t.text` discriminator is TS's `typeToString` output, which is version-sensitive (e.g. intersection-member order `{a}&{b}` vs `{b}&{a}` could canonicalize on a major bump). Verified stable across 5.9 → 6.0.3, but latent risk for names distinguishable ONLY by broken-field text.

## Proper fix (deferred — bigger/riskier)
Merge entries whose FULL `structuralSig` is genuinely identical (they're structurally interchangeable → one name, refs redirect). Needs care around the add-only `seen` diamond-collapse (`Rcyc`), which could otherwise make two genuinely-different entries look equal → unsound merge. Would fix both base-ui and blend and drop the counters entirely.

## Meanwhile
Counters here are STABLE across the 5.9 → 6.0.3 transition (deterministic sort), so no active churn today; this tracks closing the residual properly.

Start by reading the structuralSig logic from PR #140 and the add-only seen diamond-collapse path (Rcyc), then compare the base-ui menuStore and blend selectMenu cases described here. Done means genuinely identical full structural signatures can be merged safely, refs redirect, counters disappear, and the Rcyc path cannot make distinct entries appear equal.

Written by the indexing model from the issue text.