optionals: the construction surface — optional.of, ofNonZeroValue, optional.none, and friends, after traversal lands

#412's slice 1 deliberately lands traversal + orValue() only — the shapes the 68-site corpus actually uses. The owner's scope decision (2026-08-11) keeps the rest of CEL's optional-types surface on the table rather than dropped: this issue is its home.

What remains

The construction half of the extension: optional.of(), optional.ofNonZeroValue(), optional.none(), optOrValue/or() chaining between optionals, and optional-aware map/list construction ({?key: value}, [?value]).

The bar it waits behind

Same as everything in the language: corpus evidence. No shipped example or corpus workload currently constructs an optional — they read possibly-absent data, which is what slice 1 covers. When a corpus file wants to produce an absent-or-present value (a value: step that conditionally yields, a declared output that may be withheld), that file is the acceptance target and this issue activates.

Constraints already settled by #412's decisions

• The edition carries it — construction arrives as an additive extension under the same (or a later) edition, never a second dialect axis.
• Cost-bounded like everything else: construction functions meter under cel.CostLimit, with a test proving it, before any of them are reachable from a Flowfile.
• Additive only: nothing in slice 1's traversal/orValue semantics may change when construction lands.

Start by reviewing #412's slice 1 decisions and the corpus evidence described in this issue. Identify a corpus workload that constructs an optional, then use it as the acceptance target. Done means the construction functions and optional-aware collections are additive, reachable under the edition, and covered by a CEL.CostLimit test before Flowfile use.