Upgrades the 2-way body merge to a real diff3 three-way merge (review #5), so a
block ONLY the human changed is KEPT when git changed a DIFFERENT block — the
2-way merge would revert it to git's stale version.
Engine: the push update loop reads the last-synced pre-image
(`git.showFileAtRef(refs/docmost/last-pushed, path)`) and passes it as the
optional `baseMarkdown` to `client.importPageMarkdown` (the common ancestor).
Server: gitmost-datasource converts base+incoming, and writeBody runs a block-
level diff3 (new three-way-merge.ts `diff3Plan`): live-only change -> keep live,
git-only change -> take git, both-changed -> git wins (conflict policy), inserts/
deletes from either side preserved. Without a base (createPage) it falls back to
the 2-way merge. Crash-safety unchanged (docs built before the connection opens).
Tests: three-way-merge.spec.ts (14 — every diff3 case incl. the cross-block
preservation and conflict policy), yjs-body-merge 3-way (real Y.Docs: human's
block instance preserved while git's block is applied), plus an engine test that
the base is forwarded from showFileAtRef. Existing push assertions updated for the
new base arg. git-sync 589 pass; server merge/datasource/gate 62 pass; typecheck
clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Coder↔reviewer design loop (9 rounds, reviewer verdict: exhaustive) produced
92 specs; implemented +123 tests (465 -> 588 passing). The new round-trip
coverage exposed three genuine data-loss bugs in the Markdown<->ProseMirror
converter, all now FIXED (round-trip is lossless for these):
1. pageBreak was lost on export (no converter case -> rendered to "" and the
node vanished). Now emits <div data-type="pageBreak"></div>, which the schema
parses back -> round-trips.
2. A block image between blocks left an empty <p> artifact after import-hoisting,
producing a phantom blank-gap diff on every sync. markdownToProseMirror now
strips content-less paragraphs after generateJSON — with a schema-validity
guard that keeps the obligatory single empty paragraph in `content: "block+"`
containers (tableCell/tableHeader/blockquote/column/callout/doc), so empty
cells/quotes never become an invalid `content: []`.
3. The `code` mark combined with another mark was not byte-stable (emitted nested
HTML that the schema's `code` `excludes:"_"` collapsed on import). The
converter now emits code-only when `code` co-occurs, matching the editor.
New coverage spans media/diagram/details/columns/math/mention attribute
round-trips, converter emission branches, git error paths, and engine decision
branches. A dedicated test pins the empty-container schema validity (the review
catch on the bug-2 fix).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
