From b83f79cb2f9ea008e7bb88d001e224a8016bdcd1 Mon Sep 17 00:00:00 2001
From: paoloricciuti <ricciutipaolo@gmail.com>
Date: Mon, 19 Jan 2026 15:36:59 +0100
Subject: [PATCH] feat: allow `output.preventDefault` for
 `command.before.execute`

---
 .../src/cli/cmd/tui/component/prompt/index.tsx         |  6 ++++--
 packages/opencode/src/server/routes/session.ts         |  4 ++++
 packages/opencode/src/session/prompt.ts                | 10 +++++++++-
 packages/plugin/src/index.ts                           |  2 +-
 packages/sdk/js/src/v2/gen/types.gen.ts                |  4 ++++
 5 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
index 730da20c265..647f053374f 100644
--- a/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/component/prompt/index.tsx
@@ -551,8 +551,8 @@ export function Prompt(props: PromptProps) {
         return sync.data.command.some((x) => x.name === command)
       })
     ) {
-      let [command, ...args] = inputText.split(" ")
-      sdk.client.session.command({
+      const [command, ...args] = inputText.split(" ")
+      const result = await sdk.client.session.command({
         sessionID,
         command: command.slice(1),
         arguments: args.join(" "),
@@ -567,6 +567,8 @@ export function Prompt(props: PromptProps) {
             ...x,
           })),
       })
+      input.clear()
+      if (result.response.status === 204) return
     } else {
       sdk.client.session
         .prompt({
diff --git a/packages/opencode/src/server/routes/session.ts b/packages/opencode/src/server/routes/session.ts
index a98624dfae2..8a7d2ea55e1 100644
--- a/packages/opencode/src/server/routes/session.ts
+++ b/packages/opencode/src/server/routes/session.ts
@@ -782,6 +782,9 @@ export const SessionRoutes = lazy(() =>
               },
             },
           },
+          204: {
+            description: "Command execution was prevented by a plugin",
+          },
           ...errors(400, 404),
         },
       }),
@@ -796,6 +799,7 @@ export const SessionRoutes = lazy(() =>
         const sessionID = c.req.valid("param").sessionID
         const body = c.req.valid("json")
         const msg = await SessionPrompt.command({ ...body, sessionID })
+        if (!msg) return c.body(null, 204)
         return c.json(msg)
       },
     )
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index f4793d1a798..2d3e579540f 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1702,6 +1702,7 @@ NOTE: At any point in time through this workflow you should feel free to ask the
         : await lastModel(input.sessionID)
       : taskModel
 
+    let defaultPrevented = false
     await Plugin.trigger(
       "command.execute.before",
       {
@@ -1709,9 +1710,16 @@ NOTE: At any point in time through this workflow you should feel free to ask the
         sessionID: input.sessionID,
         arguments: input.arguments,
       },
-      { parts },
+      {
+        parts: parts as any,
+        preventDefault() {
+          defaultPrevented = true
+        },
+      },
     )
 
+    if (defaultPrevented) return undefined
+
     const result = (await prompt({
       sessionID: input.sessionID,
       messageID: input.messageID,
diff --git a/packages/plugin/src/index.ts b/packages/plugin/src/index.ts
index 36a4657d74c..2d5911f8437 100644
--- a/packages/plugin/src/index.ts
+++ b/packages/plugin/src/index.ts
@@ -175,7 +175,7 @@ export interface Hooks {
   "permission.ask"?: (input: Permission, output: { status: "ask" | "deny" | "allow" }) => Promise<void>
   "command.execute.before"?: (
     input: { command: string; sessionID: string; arguments: string },
-    output: { parts: Part[] },
+    output: { parts: Part[]; preventDefault(): void },
   ) => Promise<void>
   "tool.execute.before"?: (
     input: { tool: string; sessionID: string; callID: string },
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index 75540f90724..e117dbe8682 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -3504,6 +3504,10 @@ export type SessionCommandResponses = {
     info: AssistantMessage
     parts: Array<Part>
   }
+  /**
+   * Command execution was prevented by a plugin
+   */
+  204: void
 }
 
 export type SessionCommandResponse = SessionCommandResponses[keyof SessionCommandResponses]