--record-types writes 0-byte files for disabled record types

[asmacdo]

Summary

--record-types disables specific output records, but the files for the disabled records are still created — as 0-byte files. That's worse than "not created" or "valid empty document": downstream tools silently fail to parse them.

Reproducer

cd "$(mktemp -d)"
duct -t processes-samples -- bash -c 'echo ok; sleep 0.3'
ls -la .duct/logs/*_info.json         # 0 bytes

duct --clobber -t system-summary -- bash -c 'echo ok; sleep 0.3'
ls -la .duct/logs/*_usage.jsonl        # 0 bytes

Observed

• -t processes-samples: *_info.json is 0 bytes.
• -t system-summary: *_usage.jsonl is 0 bytes.
• con-duct ls over a directory containing the empty info.json silently emits nothing (parse error swallowed, no warning).

Expected

Either don't create the file at all when its record type is disabled, or emit a well-formed empty document ({} for info.json, nothing/[] for jsonl). 0-byte is the worst outcome.

Scope

Reproduces on v0.19.0 and current main. Longstanding, not a regression. Surfaced during pre-0.20.0 QE.