Type guard for inner entity maps: requires a plain object with only symbol or
non-numeric, non-empty string keys.
Rationale: Avoid ambiguity with numeric object keys (coerced to strings in JS)
and ensure predictable textual identifiers for entity keys. Matches the API
contract where inner map keys exclude number.
Parameters
value: unknown
Candidate value
Returns valueisRecord<symbol,unknown>
True if value is a valid entity record (plain + no invalid keys)
Type guard for inner entity maps: requires a plain object with only symbol or non-numeric, non-empty string keys.
Rationale: Avoid ambiguity with numeric object keys (coerced to strings in JS) and ensure predictable textual identifiers for entity keys. Matches the API contract where inner map keys exclude
number.