agent-coherence. Contact us

Blog

Notes from the write side.

Engineering notes on shared state in multi-agent systems — stale reads, lost updates, and what it takes to make agent memory safe to write to.

Four coordination mechanisms, a lock, a lease, a version check, and a fence, each labeled with the question it answers, and the zombie write slipping past the first three
fencing token · 13 min read

Lock, Lease, or Fence: Which Stops a Zombie Write?

A lock, a lease, and a fencing token answer three different questions. The write your version check passes is the one the fence refuses.

Read the post →
Two paths after a lost update: migrating to a new store repeats the race, while keeping the store and putting the version on the write resolves it with a typed conflict
optimistic concurrency · 6 min read

You Don't Need a New Store. Put the Version on the Write.

When an update vanishes the reflex is a store migration. The store was never the problem. The fix is the version on the write, over the store you already run.
A five-rung ladder of coordination pressure: from one agent and one requester, through stale reads, lost updates, and zombie writes, to the open cross-host rung
multi-agent · 7 min read

What Breaks First When Agents Share a Workspace

The failures arrive in a fixed order as an agent workspace grows: stale reads, then lost updates, then zombie writes. Find your rung and see the next one coming.
Three substrates, a Postgres row, an S3 object, and plain files, each guarded by the same coherence layer, with the coordinator holding versions and hashes but never bytes
BYO substrate · 6 min read

Shipped: coherence over the store you already run

BYO-substrate bindings are live in v0.13.0. CoherentRow guards a Postgres row, CoherentObject guards an S3 object, and the coordinator holds a version, MESI state, and a content hash, never your bytes. A peer's commit marks your cached read stale before you act on it, on a single host, with the same typed conflict and the same reacquire() recovery on every substrate.
Three shipped guarantees, version-CAS, a read fence, and invalidation-deny, each mapped to the failure it stops and the TLA+ invariant that checks it
agent memory · 6 min read

Shipped: a version check and a read fence for agents that share state

The coordination lever is live. Version-CAS, a read-generation fence, and MESI invalidation-deny stop the concurrent lost-update and the sequential stale-read-then-write on a single host, with five TLA+ invariants checking they hold.
Five ways a shared write disappears, mapped to three prevention levers: a durability receipt, a retention policy, and a coordination primitive
agent memory · 11 min read

The Silent-Data-Loss Taxonomy: Five Ways Your Agent's Write Disappears

The vanished write is not one bug. It is a class with five members, and prevention is not one lever. A durability receipt, a retention policy, and a coordination primitive split the five between them, and only the last one is the runtime's to ship.
Two agents write to the same shared record; one update lands, the other silently vanishes
agent memory · 5 min read

The write-side half of agent memory

Thirty agent-memory products describe how agents remember. Not one describes what happens when two writers hit the same key. The lost update is the half that breaks production.