feat: add threaded comments support (Excel 2019+)

[Nebu1eto]

Summary

• Add threaded comments (Excel 2019+) with conversation-style threads, replies, author tracking via shared person list, and resolved/done state
• Implement full OOXML part handling: xl/threadedComments/threadedComment{N}.xml and xl/persons/person.xml with proper content types and relationships
• Expose 7 API methods across Rust, Node.js bindings, and TypeScript wrapper: addThreadedComment, getThreadedComments, getThreadedCommentsByCell, deleteThreadedComment, resolveThreadedComment, addPerson, getPersons

Changes

XML Layer (sheetkit-xml)

• New threaded_comment.rs: ThreadedComments, ThreadedComment, PersonList, Person serde types with OOXML namespace constants

Core Layer (sheetkit-core)

• New threaded_comment.rs: business logic for add/get/delete/resolve comments, person management with auto-creation, GUID generation
• Updated workbook/io.rs: read threaded comments from worksheet rels and person list from workbook rels; write both parts with content type overrides
• Updated workbook/mod.rs: added sheet_threaded_comments and person_list fields to Workbook
• Updated workbook/sheet_ops.rs: maintain threaded comments vector in sync across new/delete/copy/stream operations
• Updated workbook/features.rs: 7 public API methods + 10 integration tests

Node.js Layer (packages/sheetkit)

• 4 napi object types in types.rs, 7 napi methods in lib.rs
• TypeScript wrapper methods in index.ts
• 10 vitest tests covering add/reply/delete/resolve/persons/round-trip

Documentation

• EN and KO threaded comments sections in docs/{en,ko}/guide/advanced.md

Test plan

• 8 XML serialization/deserialization tests
• 16 core unit tests (add, reply, get, get-by-cell, delete, resolve, person management)
• 10 integration tests (file round-trip, buffer round-trip, multi-sheet, error handling)
• 10 Node.js vitest tests (add/reply, by-cell, delete, resolve, persons, save/open round-trip)
• All quality gates pass: cargo build/test/clippy/fmt, pnpm build/test, biome check

Generated with Claude Code

[claude]

Code Review

I found 2 issues during the review:

---

Issue 1: Korean comments in code blocks (CLAUDE.md violation)

File: docs/ko/guide/advanced.md (lines 934-1010)

The code blocks contain Korean comments, which violates the project guidelines.

According to CLAUDE.md:

Documentation prose may be in other languages (e.g., Korean guide), but all code blocks within documentation must use English.

While the Korean prose in this documentation file is fine, the comments within the code examples must be in English. Please translate all inline comments in these code blocks to English.

For example:

• // 스레드 댓글 추가 (작성자는 인물 목록에 자동 추가됩니다) → // Add threaded comment (author is automatically added to person list)
• // 기존 댓글에 답글 달기 → // Reply to existing comment
• // 댓글 스레드를 해결됨으로 표시 → // Mark comment thread as resolved

---

Issue 2: Missing person list relationship in workbook_rels (bug)

File: crates/sheetkit-core/src/workbook/io.rs (lines 709-720)

The person list is written to the file but the workbook relationship is missing, which will cause Excel to fail to discover the person list.

The save code writes xl/persons/person.xml (line 849) and registers its content type (lines 709-719), but it never adds a REL_TYPE_PERSON relationship to self.workbook_rels. Without this relationship in xl/_rels/workbook.xml.rels, Excel will not discover the person list when opening the file, causing threaded comment authors to be unresolved.

The read path expects this relationship (see lines 361-391) and only uses a hardcoded fallback path. The round-trip tests pass because of this fallback, but actual Excel will not use it.

Suggested fix: Add the person relationship to workbook_rels in the has_any_threaded block after the content type override is added:

// Add person relationship to workbook_rels
if \!self.workbook_rels.relationships.iter().any(|r| {
    r.rel_type == sheetkit_xml::threaded_comment::REL_TYPE_PERSON
}) {
    let rid = crate::sheet::next_rid(&self.workbook_rels.relationships);
    self.workbook_rels.relationships.push(Relationship {
        id: rid,
        rel_type: sheetkit_xml::threaded_comment::REL_TYPE_PERSON.to_string(),
        target: "persons/person.xml".to_string(),
        target_mode: None,
    });
}

[Nebu1eto]

Review finding (blocking): threaded comment/person IDs are generated from a process-local counter. After process restart, IDs restart from the same sequence, which can collide with IDs already present in an existing workbook and produce duplicate IDs.

Relevant path: crates/sheetkit-core/src/threaded_comment.rs (generate_guid).

Please switch to collision-resistant UUID generation and ensure uniqueness against existing IDs in the target workbook.

[Nebu1eto]

Detailed review notes (blocking):

Threaded comment API is comprehensive, but ID generation strategy is unsafe.

Blocking concern:

• GUID-like IDs are generated from a process-local monotonic counter.
• After process restart, IDs start again from the same sequence and can collide with IDs already present in a workbook.

Relevant area:

• crates/sheetkit-core/src/threaded_comment.rs (generate_guid).

Expected fix:

• Use collision-resistant UUID generation.
• Before insert, enforce uniqueness against existing comment/person IDs in the workbook.

Also consider:

• Returning a not-found error for delete/resolve operations when ID does not exist (currently silent success path through workbook API).
• Validating cell reference format on add to fail early.