feat(validate): report cross-part comment inconsistencies, not only per-part schema errors #34

Version: docx-cli 0.28.0, release binary (Windows x64), Windows 11, Word 16.

What happens

docx validate reports a package as clean while Word refuses to open it without repair:

$ docx validate fixture-comments-base.docx     # after one comments add, 3 comments / 2 ids / 2 ext
valid — 6 parts checked

By design validate is a per-part ECMA-376 check (src/cli/validate/, a thin shell over
@core/raw/validate), so package-level invariants are outside what it can see. This asks for those
invariants somewhere explicit — not for the schemas to change.

Invariants worth reporting

warn  comments  comment c23 (p79) has no entry in commentsIds.xml        (22 of 25 affected)
warn  comments  comment c24 (p51) has no entry in commentsExtended.xml
warn  comments  commentRangeStart 41 has no matching commentReference

The first two are the measured failure (companion issue, filed separately, has the full numbers and a
7.6 KB fixture, #33). The third is the neighbouring class — a range whose start and end survive but whose
reference run was deleted — not observed in the document that surfaced this.

What it should not report

Measured against an 18.5 MB report, so the check does not become noise:

Where it likely lives

src/core/raw/ already runs a "reference audit" stage in the fragment gate; this is the
package-level analogue. A separate verb (docx check FILE) may fit the architecture better than
extending validate, since validate's contract is "does this part match the schema" — #31 is a good
precedent for keeping that contract narrow (there the fix preprocesses Word's shape instead of
loosening the schema).

Why it matters

The failure surfaced on the recipient's screen, not in the agent's terminal: read, diff, wc,
comments list and validate all report a healthy document. A pre-delivery check is the only step
in the loop that would have caught it.

Possible shape

• docx check FILE → exit 0 when all invariants hold, non-zero with one line per violation.
• Start with the comment-part set (highest value: it is a Word-repair trigger), then relationships
  pointing at absent parts, then commentRange* balance.
• --json for the same ack shape as the rest of the CLI.