fix(session): allow clearing archived timestamp via HTTP API

The internal session schema (UpdatedTime) supports null for the archived
field, but the HTTP API UpdatePayload schema rejects it. This means you
can archive a session via the API but cannot unarchive it.

This aligns the HTTP API schema with the internal domain model by
accepting null for the archived field in:
- UpdatePayload (httpapi/groups/session.ts)
- SetArchivedInput (session/session.ts)
- setArchived function signature (session/session.ts)

Unblocks #16030

Author: artac

packages/opencode/src/server/routes/instance/httpapi/groups/session.ts

@@ -48,7 +48,7 @@ export const UpdatePayload = Schema.Struct({
   permission: Schema.optional(Permission.Ruleset),
   time: Schema.optional(
     Schema.Struct({
-      archived: Schema.optional(Session.ArchivedTimestamp),
+      archived: Schema.optional(Schema.NullOr(Session.ArchivedTimestamp)),
     }),
   ),
 })

packages/opencode/src/session/session.ts

@@ -260,7 +260,7 @@ export const RemoveInput = SessionID
 export const SetTitleInput = Schema.Struct({ sessionID: SessionID, title: Schema.String })
 export const SetArchivedInput = Schema.Struct({
   sessionID: SessionID,
-  time: Schema.optional(ArchivedTimestamp),
+  time: Schema.optional(Schema.NullOr(ArchivedTimestamp)),
 })
 export const SetPermissionInput = Schema.Struct({
   sessionID: SessionID,
@@ -462,7 +462,7 @@ export interface Interface {
   readonly touch: (sessionID: SessionID) => Effect.Effect<void>
   readonly get: (id: SessionID) => Effect.Effect<Info, NotFound>
   readonly setTitle: (input: { sessionID: SessionID; title: string }) => Effect.Effect<void>
-  readonly setArchived: (input: { sessionID: SessionID; time?: number }) => Effect.Effect<void>
+  readonly setArchived: (input: { sessionID: SessionID; time?: number | null }) => Effect.Effect<void>
   readonly setPermission: (input: { sessionID: SessionID; permission: Permission.Ruleset }) => Effect.Effect<void>
   readonly setRevert: (input: {
     sessionID: SessionID
@@ -726,8 +726,8 @@ export const layer: Layer.Layer<
       yield* patch(input.sessionID, { title: input.title })
     })
 
-    const setArchived = Effect.fn("Session.setArchived")(function* (input: { sessionID: SessionID; time?: number }) {
-      yield* patch(input.sessionID, { time: { archived: input.time } })
+    const setArchived = Effect.fn("Session.setArchived")(function* (input: { sessionID: SessionID; time?: number | null }) {
+      yield* patch(input.sessionID, { time: { archived: input.time ?? null } })
     })
 
     const setPermission = Effect.fn("Session.setPermission")(function* (input: {

packages/opencode/test/server/global-session-list.test.ts

@@ -70,6 +70,25 @@ describe("session.listGlobal", () => {
     { git: true },
   )
 
+  it.instance(
+    "includes sessions after unarchiving",
+    () =>
+      Effect.gen(function* () {
+        const session = yield* withSession({ title: "unarchive-me" })
+
+        yield* SessionNs.Service.use((svc) => svc.setArchived({ sessionID: session.id, time: Date.now() }))
+
+        const archived = yield* Effect.sync(() => [...SessionNs.listGlobal({ limit: 200 })])
+        expect(archived.map((s) => s.id)).not.toContain(session.id)
+
+        yield* SessionNs.Service.use((svc) => svc.setArchived({ sessionID: session.id }))
+
+        const active = yield* Effect.sync(() => [...SessionNs.listGlobal({ limit: 200 })])
+        expect(active.map((s) => s.id)).toContain(session.id)
+      }),
+    { git: true },
+  )
+
   it.instance(
     "supports cursor pagination",
     () =>

packages/opencode/test/server/httpapi-session.test.ts

@@ -453,6 +453,31 @@ describe("session HttpApi", () => {
     { git: true, config: { formatter: false, lsp: false } },
   )
 
+  it.instance(
+    "clears archived timestamp when null is passed",
+    () =>
+      Effect.gen(function* () {
+        const test = yield* TestInstance
+        const headers = { "x-opencode-directory": test.directory, "content-type": "application/json" }
+        const session = yield* createSession({ title: "to-unarchive" })
+
+        yield* request(pathFor(SessionPaths.update, { sessionID: session.id }), {
+          method: "PATCH",
+          headers,
+          body: JSON.stringify({ time: { archived: Date.now() } }),
+        })
+
+        const response = yield* request(pathFor(SessionPaths.update, { sessionID: session.id }), {
+          method: "PATCH",
+          headers,
+          body: JSON.stringify({ time: { archived: null } }),
+        })
+        expect(response.status).toBe(200)
+        expect((yield* json<Session.Info>(response)).time.archived).toBeUndefined()
+      }),
+    { git: true, config: { formatter: false, lsp: false } },
+  )
+
   it.instance(
     "uses project-scoped path and directory precedence",
     () =>