Sync metadata flag conflict

Problem

Operators sometimes pass sync --metadata and sync --strip-metadata in the same invocation (copy-pasted CI flags, or “try both” locally). Without an explicit rule, it would be unclear whether structured leaves are promoted or stripped.

What we do

1. Precedence: --strip-metadata wins — leaves are written as plain strings (legacy_string mode for that run).
2. Signal: emit i18nprune.sync.metadata_flag_conflict (warning) on the CLI envelope and in human output so automation can detect ambiguous intent.
3. No hard failure: the run continues; fix flags or monitor the warning in CI.

Operator checklist

Goal	Flags
Promote/repair structured leaves	sync --metadata (and configured localeLeaves.mode if needed)
Roll back to plain strings	sync --strip-metadata only
CI strictness	jq on `.issues[]

See also

• sync command
• Locales config — leaf metadata mode
• sync issues — metadata_flag_conflict
• ADR 010 — Locale layout and metadata modes