Stdlib: sprintf and printf for HTML/template formatting

[PurHur]

Problem

Web templates often use sprintf for safe formatting:

echo sprintf('<a href="%s">%s</a>', htmlspecialchars($url), $label);

No dedicated issue tracks sprintf/printf JIT lowering; many apps avoid implode-only pipelines.

Goal

Implement sprintf (and optionally printf) for VM + JIT with a documented format subset (%s, %d, %f, %%).

Tasks

• VM: delegate to PHP sprintf initially or port minimal formatter
• JIT: LLVM builder or callout to C snprintf with bounded buffer
• Reject unsupported specifiers with clear compile/runtime errors
• PHPT compliance cases
• Document max output length (security)

Acceptance criteria

Reference app can format pagination links without string concatenation chains.

Related

• JIT Stdlib: implode, explode, and str_replace for templates and routing #82 implode/explode
• Stdlib: json_encode and json_decode for API endpoints #61 json_encode (API responses)