diff --git a/dist/server.js b/dist/server.js
index 8bf3a49..3145620 100644
--- a/dist/server.js
+++ b/dist/server.js
@@ -1353,6 +1353,9 @@ function goalCommandDefinitions(commandName) {
     }
   ];
 }
+function omitUndefined(value) {
+  return Object.fromEntries(Object.entries(value).filter(([, entry]) => entry !== undefined));
+}
 function commandNameFromOptions(options) {
   const name = options?.command_name?.trim() || DEFAULT_COMMAND_NAME;
   if (!/^[A-Za-z0-9][A-Za-z0-9._-]*$/.test(name))
@@ -3256,14 +3259,19 @@ async function setupV2(context) {
               cancelScheduledContinuation(input.sessionID);
               clearTurnWatchdog(input.sessionID);
             }
-            const stripMention = ({ mention: _mention, ...attachment }) => attachment;
+            let forwardedPrompt = {};
+            if (command.action === "goal") {
+              const stripMention = ({ mention: _mention, ...attachment }) => attachment;
+              const { files, agents, skills, ...promptFields } = input.prompt;
+              forwardedPrompt = {
+                ...omitUndefined(promptFields),
+                ...files ? { files: files.map(stripMention) } : {},
+                ...agents ? { agents: agents.map(stripMention) } : {},
+                ...skills ? { skills: skills.map(stripMention) } : {}
+              };
+            }
             await context.session.prompt({
-              ...command.action === "goal" ? {
-                ...input.prompt,
-                files: input.prompt.files?.map(stripMention),
-                agents: input.prompt.agents?.map(stripMention),
-                skills: input.prompt.skills?.map(stripMention)
-              } : {},
+              ...forwardedPrompt,
               sessionID: input.sessionID,
               text: command.template.replaceAll("$ARGUMENTS", () => input.prompt.text.trim()),
               delivery: input.delivery
diff --git a/scripts/smoke-v2-lifecycle.ts b/scripts/smoke-v2-lifecycle.ts
index 5cb4cf9..6562e91 100644
--- a/scripts/smoke-v2-lifecycle.ts
+++ b/scripts/smoke-v2-lifecycle.ts
@@ -143,7 +143,6 @@ try {
   assert(commands.data.some((command) => command.name === "goal"))
   await api(`/api/session/${sessionID}/command`, {
     command: "goal", text: "Create a goal for the fixture milestone. Keep it active until the automatic continuation arrives.",
-    files: [], agents: [], skills: [],
   })
   let state: { goals: Record<string, { status: string; autoTurns: number }> } | undefined
   await waitFor(async () => {
@@ -160,6 +159,23 @@ try {
   })
   assert.equal(state!.goals[sessionID]!.autoTurns, 2)
   assert(continuationCalls > 0)
+  const arraysSession = await api("/api/session", {
+    location: { directory: project },
+    title: "Isolated command arrays smoke",
+    model: { providerID: "fixture", id: "fixture" },
+    agent: "build",
+  }) as { data: { id: string } }
+  await api(`/api/session/${arraysSession.data.id}/command`, {
+    command: "goal",
+    text: "Create a goal for the arrays-present command smoke.",
+    files: [],
+    agents: [],
+    skills: [],
+  })
+  await waitFor(async () => {
+    try { state = JSON.parse(await readFile(env.OPENCODE_GOAL_STATE_PATH, "utf8")) } catch { return false }
+    return state?.goals[arraysSession.data.id] != null
+  })
   console.log(JSON.stringify({ result: "PASS", packagePath, sessionID, modelCalls, continuationCalls, status: state!.goals[sessionID]!.status, autoTurns: state!.goals[sessionID]!.autoTurns, artifacts: root }, null, 2))
 } finally {
   child.kill()
diff --git a/src/server.ts b/src/server.ts
index 4effa3d..b6acf9a 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -236,6 +236,10 @@ function goalCommandDefinitions(commandName: string): GoalCommandDefinition[] {
   ]
 }
 
+function omitUndefined<T extends object>(value: T): Partial<T> {
+  return Object.fromEntries(Object.entries(value).filter(([, entry]) => entry !== undefined)) as Partial<T>
+}
+
 function commandNameFromOptions(options?: Options) {
   const name = options?.command_name?.trim() || DEFAULT_COMMAND_NAME
   if (!/^[A-Za-z0-9][A-Za-z0-9._-]*$/.test(name)) return DEFAULT_COMMAND_NAME
@@ -2337,16 +2341,19 @@ async function setupV2(context: PluginV2.Plugin.Context): Promise<PluginV2.Plugi
                 cancelScheduledContinuation(input.sessionID)
                 clearTurnWatchdog(input.sessionID)
               }
-              const stripMention = <T extends { mention?: unknown }>({ mention: _mention, ...attachment }: T) => attachment
+              let forwardedPrompt: Partial<typeof input.prompt> = {}
+              if (command.action === "goal") {
+                const stripMention = <T extends { mention?: unknown }>({ mention: _mention, ...attachment }: T) => attachment
+                const { files, agents, skills, ...promptFields } = input.prompt
+                forwardedPrompt = {
+                  ...omitUndefined(promptFields),
+                  ...(files ? { files: files.map(stripMention) } : {}),
+                  ...(agents ? { agents: agents.map(stripMention) } : {}),
+                  ...(skills ? { skills: skills.map(stripMention) } : {}),
+                }
+              }
               await context.session.prompt({
-                ...(command.action === "goal"
-                  ? {
-                      ...input.prompt,
-                      files: input.prompt.files?.map(stripMention),
-                      agents: input.prompt.agents?.map(stripMention),
-                      skills: input.prompt.skills?.map(stripMention),
-                    }
-                  : {}),
+                ...forwardedPrompt,
                 sessionID: input.sessionID,
                 text: command.template.replaceAll("$ARGUMENTS", () => input.prompt.text.trim()),
                 delivery: input.delivery,
diff --git a/test/server-v2.test.ts b/test/server-v2.test.ts
index a43c819..23a62f6 100644
--- a/test/server-v2.test.ts
+++ b/test/server-v2.test.ts
@@ -371,6 +371,9 @@ test("V2 setup registers /goal, /pause_goal, and /resume_goal via command transf
 
   await command?.execute({ sessionID: "ses_empty", prompt: { text: "" }, delivery: "steer" })
   expect(mock.promptCalls[1]).toMatchObject({ sessionID: "ses_empty", delivery: "steer" })
+  expect(Object.hasOwn(mock.promptCalls[1]!, "files")).toBe(false)
+  expect(Object.hasOwn(mock.promptCalls[1]!, "agents")).toBe(false)
+  expect(Object.hasOwn(mock.promptCalls[1]!, "skills")).toBe(false)
   expect(mock.promptCalls[1]?.text).toContain("If the arguments are empty, call get_goal")
 
   await pause?.execute({
@@ -410,6 +413,44 @@ test("V2 setup preserves existing commands and configured command-name collision
   await cleanup()
 })
 
+test("V2 goal command omits undefined prompt fields and preserves empty attachment arrays", async () => {
+  const mock = makeMockContext({ auto_continue: false })
+  const cleanup = await setupPlugin(mock as never)
+  const command = mock.commands.find((candidate) => candidate.name === "goal")
+
+  await command?.execute({
+    sessionID: "ses_undefined_attachments",
+    prompt: {
+      text: "",
+      files: undefined,
+      agents: undefined,
+      skills: undefined,
+      futureOptionalField: undefined,
+      futureDefinedField: "kept",
+    } as MockPrompt & { futureOptionalField?: string; futureDefinedField?: string },
+    delivery: "queue",
+  })
+
+  expect(mock.promptCalls).toHaveLength(1)
+  expect(Object.hasOwn(mock.promptCalls[0]!, "files")).toBe(false)
+  expect(Object.hasOwn(mock.promptCalls[0]!, "agents")).toBe(false)
+  expect(Object.hasOwn(mock.promptCalls[0]!, "skills")).toBe(false)
+  expect(Object.hasOwn(mock.promptCalls[0]!, "futureOptionalField")).toBe(false)
+  expect((mock.promptCalls[0] as MockPrompt & { futureDefinedField?: string }).futureDefinedField).toBe("kept")
+
+  await command?.execute({
+    sessionID: "ses_empty_attachments",
+    prompt: { text: "", files: [], agents: [], skills: [] },
+    delivery: "queue",
+  })
+  expect(mock.promptCalls[1]?.files).toEqual([])
+  expect(mock.promptCalls[1]?.agents).toEqual([])
+  expect(mock.promptCalls[1]?.skills).toEqual([])
+
+  mock.stream.end()
+  await cleanup()
+})
+
 test("V2 prompt hook pauses compatibility commands before admission", async () => {
   const mock = makeMockContext({ auto_continue: false }, ["goal", "pause_goal", "resume_goal"])
   const cleanup = await setupPlugin(mock as never)