From 1a52e1118edf50a5fc0b0c116c5a842af25242ee Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Mon, 6 Jul 2026 13:55:47 -0400
Subject: [PATCH] refactor(core): remove unused session watermarks (#35579)

---
 packages/core/src/session.ts           | 29 +++++--------------------
 packages/core/test/session-log.test.ts | 30 --------------------------
 2 files changed, 5 insertions(+), 54 deletions(-)

diff --git a/packages/core/src/session.ts b/packages/core/src/session.ts
index 57ae67ce34..02359903e3 100644
--- a/packages/core/src/session.ts
+++ b/packages/core/src/session.ts
@@ -142,8 +142,6 @@ export type Error =
 export interface Interface {
   readonly list: (input?: ListInput) => Effect.Effect<{
     readonly data: SessionSchema.Info[]
-    /** Per-session durable log watermark, read in the same transaction as the snapshot. Sessions without events are absent. */
-    readonly watermarks: ReadonlyMap<string, EventV2.Seq>
   }>
   readonly create: (input: CreateInput) => Effect.Effect<SessionSchema.Info, NotFoundError>
   readonly fork: (input: ForkInput) => Effect.Effect<SessionSchema.Info, NotFoundError | MessageNotFoundError>
@@ -177,8 +175,6 @@ export interface Interface {
     after?: number
     follow?: boolean
   }) => Stream.Stream<SessionEvent.DurableEvent | EventLog.Synced, NotFoundError>
-  /** Latest durable log seq per session. Sessions without events are absent. */
-  readonly watermarks: (sessionIDs: ReadonlyArray<SessionSchema.ID>) => Effect.Effect<ReadonlyMap<string, EventV2.Seq>>
   readonly switchAgent: (input: { sessionID: SessionSchema.ID; agent: string }) => Effect.Effect<void, NotFoundError>
   readonly switchModel: (input: {
     sessionID: SessionSchema.ID
@@ -394,21 +390,10 @@ const layer = Layer.effect(
             order === "asc" ? asc(sortColumn) : desc(sortColumn),
             order === "asc" ? asc(SessionTable.id) : desc(SessionTable.id),
           )
-        // Watermarks must pair with the snapshot exactly, so both reads share a transaction:
-        // a higher watermark would let an attached tail skip events missing from the snapshot.
-        const snapshot = yield* db
-          .transaction(() =>
-            Effect.gen(function* () {
-              const rows = yield* (input.limit === undefined ? query.all() : query.limit(input.limit).all()).pipe(
-                Effect.orDie,
-              )
-              const watermarks = yield* events.sequences(rows.map((row) => row.id))
-              return { rows, watermarks }
-            }),
-          )
-          .pipe(Effect.orDie)
-        const rows = direction === "previous" ? snapshot.rows.toReversed() : snapshot.rows
-        return { data: rows.map((row) => fromRow(row)), watermarks: snapshot.watermarks }
+        const rows = yield* (input.limit === undefined ? query.all() : query.limit(input.limit).all()).pipe(
+          Effect.orDie,
+        )
+        return { data: (direction === "previous" ? rows.toReversed() : rows).map((row) => fromRow(row)) }
       }),
       messages: Effect.fn("V2Session.messages")(function* (input) {
         yield* result.get(input.sessionID)
@@ -463,9 +448,6 @@ const layer = Layer.effect(
               EventV2.isSynced(item) || isDurableSessionEvent(item),
           ),
         ),
-      watermarks: Effect.fn("V2Session.watermarks")(function* (sessionIDs) {
-        return yield* events.sequences(sessionIDs)
-      }),
       prompt: Effect.fn("V2Session.prompt")((input) =>
         Effect.uninterruptible(
           Effect.gen(function* () {
@@ -540,8 +522,7 @@ const layer = Layer.effect(
             const started = yield* Effect.gen(function* () {
               const shell = yield* Shell.Service
               return yield* shell.create({ command: input.command, cwd: session.location.directory })
-            })
-              .pipe(Effect.provide(locations.get(session.location)))
+            }).pipe(Effect.provide(locations.get(session.location)))
             yield* events.publish(
               SessionEvent.Shell.Started,
               {
diff --git a/packages/core/test/session-log.test.ts b/packages/core/test/session-log.test.ts
index ef0865f89e..ac2fe59496 100644
--- a/packages/core/test/session-log.test.ts
+++ b/packages/core/test/session-log.test.ts
@@ -130,33 +130,3 @@ describe("SessionV2.log", () => {
     }),
   )
 })
-
-describe("SessionV2 watermarks", () => {
-  it.effect("list pairs each session snapshot with its durable log watermark", () =>
-    Effect.gen(function* () {
-      const session = yield* SessionV2.Service
-      const events = yield* EventV2.Service
-      const first = yield* session.create({ location })
-      const second = yield* session.create({ location })
-      yield* session.rename({ sessionID: first.id, title: "session.renamed" })
-
-      const page = yield* session.list()
-      const sequences = yield* events.sequences([first.id, second.id])
-
-      expect(page.data.map((info) => info.id).toSorted()).toEqual([first.id, second.id].toSorted())
-      expect(page.watermarks).toEqual(sequences)
-      expect(page.watermarks.get(first.id)).toBeGreaterThan(page.watermarks.get(second.id)!)
-    }),
-  )
-
-  it.effect("watermarks omits sessions without durable events", () =>
-    Effect.gen(function* () {
-      const session = yield* SessionV2.Service
-      const created = yield* session.create({ location })
-
-      const watermarks = yield* session.watermarks([created.id, SessionV2.ID.create()])
-
-      expect(Array.from(watermarks.keys())).toEqual([created.id])
-    }),
-  )
-})