Bound JSON nesting before recursive metadata parsing exhausts the stack

[LunaStev]

parse_value recursively calls parse_array/parse_object, which recursively parse their elements without tracking a depth limit. Nested metadata can therefore consume call stack proportional to input nesting rather than returning a bounded parse error. The compiler uses this parser for the std manifest, so malformed or extreme input should remain an ordinary diagnostic.

No stack-overflow reproducer was run in this audit.

Source evidence at the head of #520:

• utils/src/json.rs:111 — fn parse_value
• utils/src/json.rs:223 — fn parse_array
• utils/src/json.rs:245 — fn parse_object
• front/parser/src/import.rs:726 — let manifest = utils::json::parse

Acceptance:

• Enforce a deliberate nesting bound before recursive descent, or use an iterative parser with bounded resource handling.
• Cover arrays, objects and alternating nesting immediately below/at/above the chosen limit.
• Return an error instead of a panic or process abort; include a subprocess test for very deep input where appropriate.
• Ensure accepted trees can also be safely serialized/dropped and keep the parser dependency-free.

Related: #351 addresses string decoding, not recursion/resource limits.

Audit status: identified by static source inspection; the scenarios above have not been executed during this audit. The permalink fixes the reviewed revision; this report does not claim the defect was introduced by #520.