DekaScript hard cutover: migrate @deka/json to .ds

[samifouad]

Parent: dekaruntime/deka#18

Hard-migrate @deka/json to DekaScript.

• Replace public PHPX source/tests/examples with .ds equivalents or delete obsolete material.
• Do not preserve PHPX compatibility copies.
• Record any missing .ds syntax/runtime capability as a precise upstream Deka issue.

Acceptance: json ships one public .ds implementation and DS-focused tests/docs.

[samifouad]

Cutover plan and current blocker

• Scope: replace the public JSON module implementation and all repository-facing artifacts with .ds only; no PHPX fallback, aliases, duplicate tests, examples, or compatibility docs.
• Non-goal: implement DekaScript support in this package; that belongs to dekaruntime/deka#15 and #16.
• Seam/migration: package entry must resolve index.ds through the DekaScript compiler, with no retained index.phpx. Pre-launch rollback is intentionally not applicable to the public-language contract.
• Validation: compiler/build fixture containing only deka.json and index.ds, plus module behavior tests once the compiler path exists. Review evidence will include the frozen SHA and command output.

Blocked before source changes: current compiler entry discovery accepts only app.php, index.php, and index.phpx; there is no .ds parser/resolver route. dekaruntime/deka#15 and #16 are both open; I posted the exact resolver/lifecycle repro and acceptance criteria on #16. A .ds-only change now would be non-buildable and violate the no-fallback decision. Resume this lane once those upstream changes land.

[samifouad]

Blocked: @deka/json cannot truthfully hard-cut to a runnable .ds package yet.

The actual public source is one named import/re-export of six encoding/json symbols. The stacked DS compiler work is dekaruntime/deka#15 at 97f1dae33df134d55f97674a3f5c76387dccb8b8, followed by #21 at ee5e2421d01fbd8cc25e57c244a62cb7c32e20ec. Those branches provide front-end DS parsing/lowering and stdlib bindings, but do not provide CLI/package entry resolution: #15 explicitly assigns check/run/serve/build acceptance to #16, and the stacked source still enumerates .php/.phpx package candidates and guards the build path as .phpx only.

Exact required primitive: for a manifest with "main":"index.ds", package resolution and deka run/build/serve must select and compile index.ds transitively, with no PHPX fallback. That DS entry must accept the existing named-import followed by named-re-export shape:
import { json_encode, json_decode, json_decode_result, json_last_error, json_last_error_msg, json_validate } from 'encoding/json'; export { json_encode, json_decode, json_decode_result, json_last_error, json_last_error_msg, json_validate };

No JSON files were changed; renaming it now would create a non-runnable fake conversion. Resume this lane after the resolver/lifecycle work lands and identifies its branch/SHA.