From 16cb7449f989891cd6d036660a07bdb9a43eacf8 Mon Sep 17 00:00:00 2001
From: Nick Wade <nicholas.wade@onebrief.com>
Date: Sun, 4 Jan 2026 21:00:32 -0600
Subject: [PATCH] fix: add support for ACP writeTextFile clientCapability

---
 packages/opencode/src/acp/agent.ts | 22 +++++++++++++++++++++-
 packages/opencode/src/acp/types.ts |  3 ++-
 2 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/packages/opencode/src/acp/agent.ts b/packages/opencode/src/acp/agent.ts
index bab4d2b8216..14097efc97d 100644
--- a/packages/opencode/src/acp/agent.ts
+++ b/packages/opencode/src/acp/agent.ts
@@ -323,13 +323,33 @@ export namespace ACP {
               } finally {
                 break
               }
+
+            case "file.edited":
+              if (this.config.clientCapabilities?.fs?.writeTextFile) {
+                const filepath = event.properties.file
+                try {
+                  const content = await Bun.file(filepath).text()
+                  await this.connection.writeTextFile({
+                    sessionId,
+                    path: filepath,
+                    content,
+                  })
+                  log.info("synced file edit to ACP client", { filepath, sessionId })
+                } catch (err) {
+                  log.error("failed to sync file edit to ACP client", { error: err, filepath, sessionId })
+                }
+              }
+              break
           }
         }
       })
     }
 
     async initialize(params: InitializeRequest): Promise<InitializeResponse> {
-      log.info("initialize", { protocolVersion: params.protocolVersion })
+      log.info("initialize", { protocolVersion: params.protocolVersion, clientCapabilities: params.clientCapabilities })
+
+      // Store client capabilities for use in session event handling
+      this.config.clientCapabilities = params.clientCapabilities
 
       const authMethod: AuthMethod = {
         description: "Run `opencode auth login` in the terminal",
diff --git a/packages/opencode/src/acp/types.ts b/packages/opencode/src/acp/types.ts
index 42b23091237..88b14734625 100644
--- a/packages/opencode/src/acp/types.ts
+++ b/packages/opencode/src/acp/types.ts
@@ -1,4 +1,4 @@
-import type { McpServer } from "@agentclientprotocol/sdk"
+import type { ClientCapabilities, McpServer } from "@agentclientprotocol/sdk"
 import type { OpencodeClient } from "@opencode-ai/sdk/v2"
 
 export interface ACPSessionState {
@@ -19,4 +19,5 @@ export interface ACPConfig {
     providerID: string
     modelID: string
   }
+  clientCapabilities?: ClientCapabilities
 }