[TS PBT] Search bounded generator choices while preserving dependent input structure #400

Part of the full #345 delivery. Builds on #395, #351/#352/#353 and #354. This is a required bounded research implementation, not a promise to symbolically execute arbitrary JavaScript generators.

Delivery stage

This is a stage-two extension of #345. Complete and record the core assessment in #405 before accepting this extension's end-to-end integration and results. Literature, interface design and focused experiments may start earlier; the extension never blocks #355 or #405.

Reuse the completed core contracts. This issue owns any extension-specific changes to observation, binding, scheduling, replay, shrinking and feedback integration, with focused follow-up PRs; do not retroactively broaden #351/#352 or require already completed core issues to reopen. A negative or inconclusive pilot is recorded honestly and informs design; it does not silently cancel this full-roadmap obligation.

Publish a separately identifiable extension configuration and evaluate it against the same original oracle with the extension disabled. Its final held-out evaluation belongs to #357 and is reported separately from the development pilot.

Goal

Reuse PBT generator construction semantics by searching a bounded sequence of generator choices when independent symbolic input domains lose essential structure.

Scope

• Choose and document a supported generator subset from development examples: bounded dependent tuples/collections, constrained indices, and at least one structured construction beyond independent primitives.
• Retain the concrete generator as authoritative. Expose a versioned-by-source-hash deterministic choice trace through a small adapter, with decision kind, bounds, dependencies and size/depth limits. Do not mistake a PRNG seed for an invertible description of all generator choices.
• Define the exact relation x = G(choices) for the supported construction; either lower the bounded construction to EtsIR or provide explicit checked combinator semantics. Respect concrete rejection, map/filter/chain dependencies and generation limits.
• Search choices using the original predicate or feedback target on x; replay the choice trace through the original generator, then validate x using the original property. Distinguish invalid choice traces from domain/precondition rejection and symbolic divergence.
• A bound on choice count/size defines a bounded search space. Report omitted support; no claim of full generator coverage or uniform sampling.
• Preserve useful native shrinking context when available. Integrate choice/value reduction with [TS PBT] Confirm, classify and shrink symbolic property and hypothesis witnesses #353 and prove by concrete recheck that dependent relationships and the same failure remain. Replay tokens are revision-specific.
• Compare direct domain projection, rejection-based generation and choice-space search at equal total budgets. Keep concrete-only generators usable without fabricating symbolic support.

Definition of Done

• One supported dependent generator with a nontrivial structural relationship works end to end: PBT trace, symbolic choice search, original-generator replay, original-oracle confirmation and reduction or explicit shrink limitation.
• Invalid/stale traces, filtered choices, dependence on earlier choices and bounded recursion/size have tests.
• A capability table and actual author/adapter effort are reported; unsupported native arbitrary objects/closures are explicit.
• [TS PBT] Evaluate causal contributions of property-aware feedback and bounded extensions #357 evaluates benefit and regressions on a held-out supported subset; the full version cannot substitute an unsupported-only placeholder for this implementation.