Examples: 004-ApiJson — minimal JSON API endpoint (lint-first)

[PurHur]

Problem

Shipped examples stop at HTML pages (001-SimpleWeb, 002-StaticWeb). The north-star app (#67) needs a /api/status JSON route, but there is no small example that drives json_encode, http_response_code, and Content-Type: application/json through phpc lint / ExamplesCompileTest.

Goal

Add examples/004-ApiJson/example.php as a lint-first stub (like #246 for MiniWebApp):

header('Content-Type: application/json');
http_response_code(200);
echo json_encode(['ok' => true, 'service' => 'php-compiler']);

Start with phpc lint --json listing blockers; expand to VM smoke, then JIT/AOT when #61 / #252 close.

Scope

• examples/004-ApiJson/example.php + README.md (curl + phpc run recipes)
• Register in ExamplesCompileTest via glob (automatic)
• README blocker table linking Stdlib: json_encode and json_decode for API endpoints #61, Stdlib: http_response_code() for 404/500 and API status #252, Compiler: VM/JIT comparison and equality for mixed types (routing guards) #90 (routing guards), Language: JIT support for non-void function return types #55 (helper returns)
• Optional: test/real/cases/api_json_smoke.phpt when VM builtins land

Acceptance criteria

Today (blockers expected):

docker run --rm -v "$(pwd):/compiler" -w /compiler php-compiler:22.04-dev \
  ./phpc lint examples/004-ApiJson/example.php

exits 0 with structured unsupported nodes OR exits 0 with clean lint once blockers close.

When #61 + #252 land:

./phpc run examples/004-ApiJson/example.php

prints valid JSON; curl via phpc serve returns application/json.

Dependencies

• Stdlib: json_encode and json_decode for API endpoints #61 json_encode / json_decode
• Stdlib: http_response_code() for 404/500 and API status #252 http_response_code()
• Reference app: examples/003-MiniWebApp (router, templates, forms) #67 / Web: MiniWebApp routing pattern (front controller + path dispatch) #210 reference app consumes this pattern

Links

• examples/README.md, Docs: examples/README — phpc/vm/aot run matrix per example folder #262, Reference: MiniWebApp lint-first skeleton (examples/003-MiniWebApp) #246, 🗺️ ROADMAP: Compile a small PHP web application (living document) #78 ROADMAP

[PurHur]

Merged in #389: examples/004-ApiJson lint/smoke/AOT gate.