feat: add typed Result and ownership-safe propagation

[fffonion]

Summary

• Add typed Result<T, E>, Ok/Err, exhaustive destructuring and lexical ? propagation, preserving active-payload ownership and cleanup.
• Integrate the explicit guest Result host SDK, macro/catalog contracts, current v13 wire consumers, diagnostics/type hints/formatting, wasm consumers and executable documentation.
• Close the final diagnostic-provenance and HTTP retirement regressions: argument-qualified canonical rejection, preserved independent ownership checks, and one private original-native-join completion owner shared by buffered HTTP and SSE.

Stack

Depends on #33. Base is feat/generic-typed-frontends at 47cac633cde1f9cb67607141e0a6cfe9103ca4a468, not master. The published merge joins accepted SDK/R2 integration 0fe8343256481c435929e4cc90b36da730144544 with language-service commit 5d65a8553c6a3b697906447024ab2cfba3f48b7c and the reviewed final R4 changes.

Verification

All 36 required local R4 intents have current source-bound successful receipts on the reviewed candidate:

• Default workspace: 2631 passed, 0 failed (15 ignored, 14 filtered).
• All-feature normal-parallel and serial: 2826 passed, 0 failed each (15 ignored, 45 filtered).
• Strict Clippy, formatting, applicable no-runtime/no-std checks, actual wasm32 builds and six exported wasm ABI lanes.
• Native payload 60, resource-lifetime 6 and AOT SSA/runtime 18 observations; macro UI 19 negative and 3 positive cases.
• Real buffered normal/reset native-tail RED-to-GREEN; complete buffered serial/parallel repetitions and four complete normal-parallel SSE runs. Additional parent precommit HTTP and SDK/propagation gates passed.
• Two product-documentation tests passed. The runnable doctest inventory is zero; a successful docs command is not counted as executed doctests.

The full reviewed eligible source bytes were compared directly with the committed Git objects. Independent whole-change and scoped Grok spec/quality reviews have no remaining delivery blocker. Historical failed/interrupted attempts remain separate from final-source passes.

Exact-head CI for 7906820cd472e6f7a606f0a2d257f4a3b71cffed is in progress: https://github.com/rustscript-lang/rustscript/actions/runs/39099423490 . Local source validation and review do not certify that pending run or close the downstream SDK/ES5 dependency barrier.

Retained boundaries

• VMBC remains the selected current v13 contract; no new Value variant, opcode or JS-specific Core semantics.
• Trace resource move helpers and Err cleanup Ret may use interpreter boundaries. Existing StringGet/Tagged-arithmetic refusals and the extra unhinted AOT Add limitation remain explicit.
• Cost evidence is shared-host debug characterization (144 samples), not isolated release throughput or a zero-cost claim.
• Existing no-std resource-cleanup and diagnostic-extent qualifications, plus nonblocking review advisories, remain documented.
• ES5.1 frontend work and its later exception integration are separate scopes.