feat(acp): add session/list and session/fork support (#7976)

3 files changed, 150 insertions, 5 deletions

diff --git a/bun.lock b/bun.lock
index b06c04809..403427ff6 100644
--- a/bun.lock
+++ b/bun.lock
@@ -263,7 +263,7 @@
       "dependencies": {
         "@actions/core": "1.11.1",
         "@actions/github": "6.0.1",
-        "@agentclientprotocol/sdk": "0.5.1",
+        "@agentclientprotocol/sdk": "0.12.0",
         "@ai-sdk/amazon-bedrock": "3.0.73",
         "@ai-sdk/anthropic": "2.0.57",
         "@ai-sdk/azure": "2.0.91",
@@ -554,7 +554,7 @@
 
     "@adobe/css-tools": ["@adobe/[email protected]", "", {}, "sha512-Elp+iwUx5rN5+Y8xLt5/GRoG20WGoDCQ/1Fb+1LiGtvwbDavuSk0jhD/eZdckHAuzcDzccnkv+rEjyWfRx18gg=="],
 
-    "@agentclientprotocol/sdk": ["@agentclientprotocol/[email protected]", "", { "dependencies": { "zod": "^3.0.0" } }, "sha512-9bq2TgjhLBSUSC5jE04MEe+Hqw8YePzKghhYZ9QcjOyonY3q2oJfX6GoSO83hURpEnsqEPIrex6VZN3+61fBJg=="],
+    "@agentclientprotocol/sdk": ["@agentclientprotocol/[email protected]", "", { "peerDependencies": { "zod": "^3.25.0 || ^4.0.0" } }, "sha512-V8uH/KK1t7utqyJmTA7y7DzKu6+jKFIXM+ZVouz8E55j8Ej2RV42rEvPKn3/PpBJlliI5crcGk1qQhZ7VwaepA=="],
 
     "@ai-sdk/amazon-bedrock": ["@ai-sdk/[email protected]", "", { "dependencies": { "@ai-sdk/anthropic": "2.0.57", "@ai-sdk/provider": "2.0.1", "@ai-sdk/provider-utils": "3.0.20", "@smithy/eventstream-codec": "^4.0.1", "@smithy/util-utf8": "^4.0.0", "aws4fetch": "^1.0.20" }, "peerDependencies": { "zod": "^3.25.76 || ^4.1.8" } }, "sha512-EAAGJ/dfbAZaqIhK3w52hq6cftSLZwXdC6uHKh8Cls1T0N4MxS6ykDf54UyFO3bZWkQxR+Mdw1B3qireGOxtJQ=="],
 
@@ -3978,8 +3978,6 @@
 
     "@actions/http-client/undici": ["[email protected]", "", { "dependencies": { "@fastify/busboy": "^2.0.0" } }, "sha512-raqeBD6NQK4SkWhQzeYKd1KmIG6dllBOTt55Rmkt4HtI9mwdWtJljnrXjAFUBLTSN67HWrOIZ3EPF4kjUw80Bg=="],
 
-    "@agentclientprotocol/sdk/zod": ["[email protected]", "", {}, "sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ=="],
-
     "@ai-sdk/amazon-bedrock/@ai-sdk/anthropic": ["@ai-sdk/[email protected]", "", { "dependencies": { "@ai-sdk/provider": "2.0.1", "@ai-sdk/provider-utils": "3.0.20" }, "peerDependencies": { "zod": "^3.25.76 || ^4.1.8" } }, "sha512-DREpYqW2pylgaj69gZ+K8u92bo9DaMgFdictYnY+IwYeY3bawQ4zI7l/o1VkDsBDljAx8iYz5lPURwVZNu+Xpg=="],
 
     "@ai-sdk/amazon-bedrock/@smithy/eventstream-codec": ["@smithy/[email protected]", "", { "dependencies": { "@aws-crypto/crc32": "5.2.0", "@smithy/types": "^4.9.0", "@smithy/util-hex-encoding": "^4.2.0", "tslib": "^2.6.2" } }, "sha512-Ogt4Zi9hEbIP17oQMd68qYOHUzmH47UkK7q7Gl55iIm9oKt27MUGrC5JfpMroeHjdkOliOA4Qt3NQ1xMq/nrlA=="],
diff --git a/packages/opencode/package.json b/packages/opencode/package.json
index a76099905..c2eaccbf3 100644
--- a/packages/opencode/package.json
+++ b/packages/opencode/package.json
@@ -49,7 +49,7 @@
   "dependencies": {
     "@actions/core": "1.11.1",
     "@actions/github": "6.0.1",
-    "@agentclientprotocol/sdk": "0.5.1",
+    "@agentclientprotocol/sdk": "0.12.0",
     "@ai-sdk/amazon-bedrock": "3.0.73",
     "@ai-sdk/anthropic": "2.0.57",
     "@ai-sdk/azure": "2.0.91",
diff --git a/packages/opencode/src/acp/agent.ts b/packages/opencode/src/acp/agent.ts
index 0f5f23bfe..e165509b9 100644
--- a/packages/opencode/src/acp/agent.ts
+++ b/packages/opencode/src/acp/agent.ts
@@ -5,14 +5,21 @@ import {
   type AuthenticateRequest,
   type AuthMethod,
   type CancelNotification,
+  type ForkSessionRequest,
+  type ForkSessionResponse,
   type InitializeRequest,
   type InitializeResponse,
+  type ListSessionsRequest,
+  type ListSessionsResponse,
   type LoadSessionRequest,
   type NewSessionRequest,
   type PermissionOption,
   type PlanEntry,
   type PromptRequest,
+  type ResumeSessionRequest,
+  type ResumeSessionResponse,
   type Role,
+  type SessionInfo,
   type SetSessionModelRequest,
   type SetSessionModeRequest,
   type SetSessionModeResponse,
@@ -430,6 +437,11 @@ export namespace ACP {
             embeddedContext: true,
             image: true,
           },
+          sessionCapabilities: {
+            fork: {},
+            list: {},
+            resume: {},
+          },
         },
         authMethods: [authMethod],
         agentInfo: {
@@ -540,6 +552,141 @@ export namespace ACP {
       }
     }
 
+    async unstable_listSessions(params: ListSessionsRequest): Promise<ListSessionsResponse> {
+      try {
+        const cursor = params.cursor ? Number(params.cursor) : undefined
+        const limit = 100
+
+        const sessions = await this.sdk.session
+          .list(
+            {
+              directory: params.cwd ?? undefined,
+              roots: true,
+            },
+            { throwOnError: true },
+          )
+          .then((x) => x.data ?? [])
+
+        const sorted = sessions.toSorted((a, b) => b.time.updated - a.time.updated)
+        const filtered = cursor ? sorted.filter((s) => s.time.updated < cursor) : sorted
+        const page = filtered.slice(0, limit)
+
+        const entries: SessionInfo[] = page.map((session) => ({
+          sessionId: session.id,
+          cwd: session.directory,
+          title: session.title,
+          updatedAt: new Date(session.time.updated).toISOString(),
+        }))
+
+        const last = page[page.length - 1]
+        const next = filtered.length > limit && last ? String(last.time.updated) : undefined
+
+        const response: ListSessionsResponse = {
+          sessions: entries,
+        }
+        if (next) response.nextCursor = next
+        return response
+      } catch (e) {
+        const error = MessageV2.fromError(e, {
+          providerID: this.config.defaultModel?.providerID ?? "unknown",
+        })
+        if (LoadAPIKeyError.isInstance(error)) {
+          throw RequestError.authRequired()
+        }
+        throw e
+      }
+    }
+
+    async unstable_forkSession(params: ForkSessionRequest): Promise<ForkSessionResponse> {
+      const directory = params.cwd
+      const mcpServers = params.mcpServers ?? []
+
+      try {
+        const model = await defaultModel(this.config, directory)
+
+        const forked = await this.sdk.session
+          .fork(
+            {
+              sessionID: params.sessionId,
+              directory,
+            },
+            { throwOnError: true },
+          )
+          .then((x) => x.data)
+
+        if (!forked) {
+          throw new Error("Fork session returned no data")
+        }
+
+        const sessionId = forked.id
+        await this.sessionManager.load(sessionId, directory, mcpServers, model)
+
+        log.info("fork_session", { sessionId, mcpServers: mcpServers.length })
+
+        const mode = await this.loadSessionMode({
+          cwd: directory,
+          mcpServers,
+          sessionId,
+        })
+
+        const messages = await this.sdk.session
+          .messages(
+            {
+              sessionID: sessionId,
+              directory,
+            },
+            { throwOnError: true },
+          )
+          .then((x) => x.data)
+          .catch((err) => {
+            log.error("unexpected error when fetching message", { error: err })
+            return undefined
+          })
+
+        for (const msg of messages ?? []) {
+          log.debug("replay message", msg)
+          await this.processMessage(msg)
+        }
+
+        return mode
+      } catch (e) {
+        const error = MessageV2.fromError(e, {
+          providerID: this.config.defaultModel?.providerID ?? "unknown",
+        })
+        if (LoadAPIKeyError.isInstance(error)) {
+          throw RequestError.authRequired()
+        }
+        throw e
+      }
+    }
+
+    async unstable_resumeSession(params: ResumeSessionRequest): Promise<ResumeSessionResponse> {
+      const directory = params.cwd
+      const sessionId = params.sessionId
+      const mcpServers = params.mcpServers ?? []
+
+      try {
+        const model = await defaultModel(this.config, directory)
+        await this.sessionManager.load(sessionId, directory, mcpServers, model)
+
+        log.info("resume_session", { sessionId, mcpServers: mcpServers.length })
+
+        return this.loadSessionMode({
+          cwd: directory,
+          mcpServers,
+          sessionId,
+        })
+      } catch (e) {
+        const error = MessageV2.fromError(e, {
+          providerID: this.config.defaultModel?.providerID ?? "unknown",
+        })
+        if (LoadAPIKeyError.isInstance(error)) {
+          throw RequestError.authRequired()
+        }
+        throw e
+      }
+    }
+
     private async processMessage(message: SessionMessageResponse) {
       log.debug("process message", message)
       if (message.info.role !== "assistant" && message.info.role !== "user") return