[Bug]: content-ops stdin JSON input is read without a size limit #6089

Preflight

• I searched existing issues and discussions for this behavior.
• This report is not an unpatched security vulnerability.
• The report and attachments contain no credentials or private/internal material.

Issue origin

Observed or reproduced in a real environment

LoopX version or commit

main @ 07eb7a1

Host or runtime surface

Not host-specific

LoopX area

Capability or extension (providers, adapters, skills)

Problem

loopx/capabilities/content_ops/cli.py::_load_json_object reads stdin with sys.stdin.read() before parsing JSON, with no maximum size. The queue-status and item-transition commands explicitly accept - for JSON input, so a piped oversized payload is fully buffered in memory before validation. A very large or accidentally unbounded input can exhaust memory in this CLI process. This issue is limited to the stdin path; it does not claim that every JSON file reader should share one universal limit.

Minimal reproduction

On main at 07eb7a1288e8a33995493f9d50475f2664fcbf2e, run a content-ops command that accepts --item-json - and pipe an input stream larger than the desired CLI input bound. _load_json_object calls sys.stdin.read() without a byte limit, so it buffers the entire stream before json.loads runs.

Expected behavior

The stdin reader should enforce a documented maximum byte size and return a clear validation error when the limit is exceeded, before allocating the complete input in memory.

Actual behavior

The - branch invokes json.loads(sys.stdin.read()) directly. It has no bounded read or pre-parse size check.

Sanitized diagnostics

Confirmed by source inspection on synthetic input; no private files, credentials, or runtime state involved.

Additional context

No response