diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index c29733999214..f287f01a2391 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1870,7 +1870,157 @@ NOTE: At any point in time through this workflow you should feel free to ask the
   export type CommandInput = z.infer<typeof CommandInput>
 
   export async function command(input: CommandInput) {
-    return runPromise((svc) => svc.command(CommandInput.parse(input)))
+    log.info("command", input)
+    const command = await Command.get(input.command)
+    const agentName = command.agent ?? input.agent ?? (await Agent.defaultAgent())
+
+    const raw = input.arguments.match(argsRegex) ?? []
+    const args = raw.map((arg) => arg.replace(quoteTrimRegex, ""))
+
+    const templateCommand = await command.template
+
+    const placeholders = templateCommand.match(placeholderRegex) ?? []
+    let last = 0
+    for (const item of placeholders) {
+      const value = Number(item.slice(1))
+      if (value > last) last = value
+    }
+
+    // Let the final placeholder swallow any extra arguments so prompts read naturally
+    const withArgs = templateCommand.replaceAll(placeholderRegex, (_, index) => {
+      const position = Number(index)
+      const argIndex = position - 1
+      if (argIndex >= args.length) return ""
+      if (position === last) return args.slice(argIndex).join(" ")
+      return args[argIndex]
+    })
+    const usesArgumentsPlaceholder = templateCommand.includes("$ARGUMENTS")
+    let template = withArgs.replaceAll("$ARGUMENTS", input.arguments)
+
+    // If command doesn't explicitly handle arguments (no $N or $ARGUMENTS placeholders)
+    // but user provided arguments, append them to the template
+    if (placeholders.length === 0 && !usesArgumentsPlaceholder && input.arguments.trim()) {
+      template = template + "\n\n" + input.arguments
+    }
+
+    const shell = ConfigMarkdown.shell(template)
+    if (shell.length > 0) {
+      const results = await Promise.all(
+        shell.map(async ([, cmd]) => {
+          try {
+            return await $`${{ raw: cmd }}`.quiet().nothrow().text()
+          } catch (error) {
+            return `Error executing command: ${error instanceof Error ? error.message : String(error)}`
+          }
+        }),
+      )
+      let index = 0
+      template = template.replace(bashRegex, () => results[index++])
+    }
+    template = template.trim()
+
+    const agent = await Agent.get(agentName)
+    const isSubtask = (agent?.mode === "subagent" && command.subtask !== false) || command.subtask === true
+
+    const taskModel = await (async () => {
+      if (isSubtask) {
+        if (command.model) return Provider.parseModel(command.model)
+        if (command.agent) {
+          const m = command.agent === agentName
+            ? agent?.model
+            : (await Agent.get(command.agent))?.model
+          if (m) return m
+        }
+        if (input.model) return Provider.parseModel(input.model)
+        return await lastModel(input.sessionID)
+      }
+      if (input.model) return Provider.parseModel(input.model)
+      if (command.model) return Provider.parseModel(command.model)
+      if (command.agent) {
+        const m = command.agent === agentName
+          ? agent?.model
+          : (await Agent.get(command.agent))?.model
+        if (m) return m
+      }
+      return await lastModel(input.sessionID)
+    })()
+
+    try {
+      await Provider.getModel(taskModel.providerID, taskModel.modelID)
+    } catch (e) {
+      if (Provider.ModelNotFoundError.isInstance(e)) {
+        const { providerID, modelID, suggestions } = e.data
+        const hint = suggestions?.length ? ` Did you mean: ${suggestions.join(", ")}?` : ""
+        Bus.publish(Session.Event.Error, {
+          sessionID: input.sessionID,
+          error: new NamedError.Unknown({ message: `Model not found: ${providerID}/${modelID}.${hint}` }).toObject(),
+        })
+      }
+      throw e
+    }
+    if (!agent) {
+      const available = await Agent.list().then((agents) => agents.filter((a) => !a.hidden).map((a) => a.name))
+      const hint = available.length ? ` Available agents: ${available.join(", ")}` : ""
+      const error = new NamedError.Unknown({ message: `Agent not found: "${agentName}".${hint}` })
+      Bus.publish(Session.Event.Error, {
+        sessionID: input.sessionID,
+        error: error.toObject(),
+      })
+      throw error
+    }
+
+    const templateParts = await resolvePromptParts(template)
+    const parts = isSubtask
+      ? [
+          {
+            type: "subtask" as const,
+            agent: agent.name,
+            description: command.description ?? "",
+            command: input.command,
+            model: {
+              providerID: taskModel.providerID,
+              modelID: taskModel.modelID,
+            },
+            // TODO: how can we make task tool accept a more complex input?
+            prompt: templateParts.find((y) => y.type === "text")?.text ?? "",
+          },
+        ]
+      : [...templateParts, ...(input.parts ?? [])]
+
+    const userAgent = isSubtask ? (input.agent ?? (await Agent.defaultAgent())) : agentName
+    const userModel = isSubtask
+      ? input.model
+        ? Provider.parseModel(input.model)
+        : await lastModel(input.sessionID)
+      : taskModel
+
+    await Plugin.trigger(
+      "command.execute.before",
+      {
+        command: input.command,
+        sessionID: input.sessionID,
+        arguments: input.arguments,
+      },
+      { parts },
+    )
+
+    const result = (await prompt({
+      sessionID: input.sessionID,
+      messageID: input.messageID,
+      model: userModel,
+      agent: userAgent,
+      parts,
+      variant: input.variant,
+    })) as MessageV2.WithParts
+
+    Bus.publish(Command.Event.Executed, {
+      name: input.command,
+      sessionID: input.sessionID,
+      arguments: input.arguments,
+      messageID: result.info.id,
+    })
+
+    return result
   }
 
   /** @internal Exported for testing */