## Why
Filesystem denials and managed-network blocks did not share a structured event
shape, requiring downstream consumers to rediscover enforcement paths and parse
backend-specific output. See https://github.com/openai/codex/pull/17573.
## What changed
- Add normalized filesystem and network violation types in `codex-sandboxing`
and emit them through a shared tracing seam.
- Classify filesystem denials by backend and reason, retaining an optional path
and bounded output snippet, and preserve managed-network block context.
- Report the sandbox type through exec-server responses so unified exec can
classify remote denials without guessing; omitted values remain compatible
with older peers.
- Record violations from exec, apply-patch, shell-escalation, unified-exec, and
managed-network enforcement paths without changing denial behavior.
## Testing
- Cover filesystem classification, path extraction, `SIGSYS`, network event
conversion, protocol compatibility, and remote sandbox-type propagation.
GitOrigin-RevId: d673173b4fa6bdf0a24421194a8a61c81fab9c96
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