feat(opencode): add experimental code-mode MCP adapter

packages/opencode/package.json

@@ -84,6 +84,7 @@
     "@octokit/graphql": "9.0.2",
     "@octokit/rest": "catalog:",
     "@openauthjs/openauth": "catalog:",
+    "@opencode-ai/codemode": "workspace:*",
     "@opencode-ai/llm": "workspace:*",
     "@opencode-ai/plugin": "workspace:*",
     "@opencode-ai/protocol": "workspace:*",

packages/opencode/src/effect/runtime-flags.ts

@@ -43,6 +43,7 @@ export class Service extends ConfigService.Service<Service>()("@opencode/Runtime
   experimentalBackgroundSubagents: enabledByExperimental("OPENCODE_EXPERIMENTAL_BACKGROUND_SUBAGENTS"),
   experimentalLspTy: bool("OPENCODE_EXPERIMENTAL_LSP_TY"),
   experimentalLspTool: enabledByExperimental("OPENCODE_EXPERIMENTAL_LSP_TOOL"),
+  experimentalCodeMode: enabledByExperimental("OPENCODE_EXPERIMENTAL_CODE_MODE"),
   experimentalOxfmt: enabledByExperimental("OPENCODE_EXPERIMENTAL_OXFMT"),
   experimentalPlanMode: enabledByExperimental("OPENCODE_EXPERIMENTAL_PLAN_MODE"),
   experimentalEventSystem: enabledByExperimental("OPENCODE_EXPERIMENTAL_EVENT_SYSTEM"),

packages/opencode/src/mcp/index.ts

@@ -159,6 +159,12 @@ export interface Interface {
   readonly clients: () => Effect.Effect<Record<string, MCPClient>>
   readonly instructions: () => Effect.Effect<ServerInstructions[]>
   readonly tools: () => Effect.Effect<Record<string, Tool>>
+  /**
+   * Raw MCP tool definitions keyed identically to {@link tools} (`toolName(client, name)`).
+   * Unlike {@link tools}, these retain the original `inputSchema`/`outputSchema`, which code
+   * mode uses to render tool signatures (including return types) to the model.
+   */
+  readonly defs: () => Effect.Effect<Record<string, MCPToolDef>>
   readonly prompts: () => Effect.Effect<Record<string, PromptInfo & { client: string }>>
   readonly resources: (clientName?: string) => Effect.Effect<Record<string, ResourceInfo & { client: string }>>
   readonly resourceTemplates: (
@@ -680,6 +686,18 @@ const layer = Layer.effect(
       return result
     })
 
+    const defs = Effect.fn("MCP.defs")(function* () {
+      const result: Record<string, MCPToolDef> = {}
+      const s = yield* InstanceState.get(state)
+      for (const [clientName, listed] of Object.entries(s.defs)) {
+        if (s.status[clientName]?.status !== "connected") continue
+        for (const mcpTool of listed) {
+          result[McpCatalog.toolName(clientName, mcpTool.name)] = mcpTool
+        }
+      }
+      return result
+    })
+
     function collectFromConnected<T extends { name: string }>(
       s: State,
       listFn: (c: Client, timeout?: number) => Promise<T[]>,
@@ -982,6 +1000,7 @@ const layer = Layer.effect(
       clients,
       instructions,
       tools,
+      defs,
       prompts,
       resources,
       resourceTemplates,

packages/opencode/src/mcp/invoke.ts

@@ -0,0 +1,65 @@
+import type { ToolExecutionOptions } from "ai"
+import { Effect } from "effect"
+import type { Plugin } from "@/plugin"
+import type { Tool } from "@/tool/tool"
+
+/**
+ * The shared middle of every raw MCP tool invocation: plugin `tool.execute.before`
+ * hook → permission ask → dispatch through the ai-sdk tool's execute inside the
+ * `Tool.execute` tracing span → plugin `tool.execute.after` hook. Used by both the
+ * legacy per-tool registration in `SessionTools.resolve` and code-mode child calls,
+ * so MCP tools execute identically on either path.
+ *
+ * Returns the RAW result the ai-sdk execute resolved with — callers own their
+ * shaping edge (model-facing text/attachment shaping + truncation on the legacy
+ * path, `toSandboxResult` for code-mode child calls). The after hook fires here
+ * with that same raw result, which is exactly what the legacy loop always passed
+ * (the raw MCP result, not the shaped `{title, output, metadata}`), so the hook
+ * payload cannot drift between callers.
+ *
+ * `callID` is the hook/span identity — an opaque string nothing parses. Legacy
+ * passes the ai-sdk `toolCallId`; code-mode child calls pass a synthetic
+ * `${parentCallID}/${n}`. `options.toolCallId` is what the ai-sdk execute sees and
+ * stays each caller's existing value. Failure semantics belong to the caller: hook
+ * failures, permission denials, and tool failures all propagate — the legacy path
+ * lets them fail the tool call as before; code mode converts them into catchable
+ * in-program tool errors at its edge.
+ */
+export const invoke = Effect.fn("McpInvoke.invoke")(function* <R>(input: {
+  plugin: Plugin.Interface
+  key: string
+  execute: (args: any, options: ToolExecutionOptions) => R | PromiseLike<R>
+  args: any
+  callID: string
+  options: ToolExecutionOptions
+  sessionID: string
+  messageID: string
+  ask: Tool.Context["ask"]
+}) {
+  yield* input.plugin.trigger(
+    "tool.execute.before",
+    { tool: input.key, sessionID: input.sessionID, callID: input.callID },
+    { args: input.args },
+  )
+  const result: R = yield* Effect.gen(function* () {
+    yield* input.ask({ permission: input.key, metadata: {}, patterns: ["*"], always: ["*"] })
+    return yield* Effect.promise(() => Promise.resolve(input.execute(input.args, input.options)))
+  }).pipe(
+    Effect.withSpan("Tool.execute", {
+      attributes: {
+        "tool.name": input.key,
+        "tool.call_id": input.callID,
+        "session.id": input.sessionID,
+        "message.id": input.messageID,
+      },
+    }),
+  )
+  yield* input.plugin.trigger(
+    "tool.execute.after",
+    { tool: input.key, sessionID: input.sessionID, callID: input.callID, args: input.args },
+    result,
+  )
+  return result
+})
+
+export * as McpInvoke from "./invoke"

packages/opencode/src/permission/index.ts

@@ -213,6 +213,18 @@ export function disabled(tools: string[], ruleset: PermissionV1.Ruleset): Set<st
   )
 }
 
+/**
+ * The shared tool-visibility predicate: drop every tool a hard deny hides
+ * ({@link disabled} semantics — a matching `deny` rule with pattern `"*"`).
+ * Ask-level rules leave a tool fully visible and callable (it prompts at call
+ * time). Used both when preparing the LLM tool list (request prep) and when
+ * building/dispatching the code-mode MCP catalog, so the two cannot drift.
+ */
+export function visibleTools<T>(tools: Record<string, T>, ruleset: PermissionV1.Ruleset): Record<string, T> {
+  const hidden = disabled(Object.keys(tools), ruleset)
+  return Object.fromEntries(Object.entries(tools).filter(([name]) => !hidden.has(name)))
+}
+
 export const node = LayerNode.make({ service: Service, layer: layer, deps: [EventV2Bridge.node] })
 
 export * as Permission from "."

packages/opencode/src/session/llm/request.ts

@@ -206,11 +206,11 @@ export const prepare = Effect.fn("LLMRequestPrep.prepare")(function* (input: Pre
 })
 
 function resolveTools(input: Pick<PrepareInput, "tools" | "agent" | "permission" | "user">) {
-  const disabled = Permission.disabled(
-    Object.keys(input.tools),
+  const visible = Permission.visibleTools(
+    input.tools,
     Permission.merge(input.agent.permission, input.permission ?? []),
   )
-  return Record.filter(input.tools, (_, k) => input.user.tools?.[k] !== false && !disabled.has(k))
+  return Record.filter(visible, (_, k) => input.user.tools?.[k] !== false)
 }
 
 export function hasToolCalls(messages: ModelMessage[]): boolean {

packages/opencode/src/session/prompt.ts

@@ -1237,6 +1237,8 @@ const layer = Layer.effect(
               Effect.provideService(ToolRegistry.Service, registry),
               Effect.provideService(MCP.Service, mcp),
               Effect.provideService(Truncate.Service, truncate),
+              Effect.provideService(Agent.Service, agents),
+              Effect.provideService(RuntimeFlags.Service, flags),
             )
 
             if (lastUser.format?.type === "json_schema") {

packages/opencode/src/session/tools.ts

@@ -3,6 +3,7 @@ import { SessionV1 } from "@opencode-ai/core/v1/session"
 import { Provider } from "@/provider/provider"
 import { ProviderTransform } from "@/provider/transform"
 import { MCP } from "@/mcp"
+import { McpInvoke } from "@/mcp/invoke"
 import { Permission } from "@/permission"
 import { Tool } from "@/tool/tool"
 import { ToolJsonSchema } from "@/tool/json-schema"
@@ -21,6 +22,7 @@ import { EffectBridge } from "@/effect/bridge"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { ModelV2 } from "@opencode-ai/core/model"
 import { isRecord } from "@/util/record"
+import { RuntimeFlags } from "@/effect/runtime-flags"
 
 const MCP_RESOURCE_TOOLS = {
   list: "list_mcp_resources",
@@ -52,6 +54,7 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
   const registry = yield* ToolRegistry.Service
   const mcp = yield* MCP.Service
   const truncate = yield* Truncate.Service
+  const flags = yield* RuntimeFlags.Service
 
   const context = (args: Record<string, unknown>, options: ToolExecutionOptions): Tool.Context => ({
     sessionID: input.session.id,
@@ -86,11 +89,20 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
         .pipe(Effect.orDie),
   })
 
-  for (const item of yield* registry.tools({
+  const mcpTools = yield* mcp.tools()
+  // When code mode is enabled and MCP tools are present, the registry exposes them
+  // through the single code-mode `execute` tool (ToolRegistry.tools), so raw per-MCP
+  // registration is suppressed via the early return below. Code mode is experimental
+  // and off by default.
+  const codeMode = flags.experimentalCodeMode && Object.keys(mcpTools).length > 0
+  const registryTools = yield* registry.tools({
     modelID: ModelV2.ID.make(input.model.api.id),
     providerID: input.model.providerID,
     agent: input.agent,
-  })) {
+    permission: input.session.permission,
+  })
+
+  for (const item of registryTools) {
     const schema = ProviderTransform.schema(input.model, ToolJsonSchema.fromTool(item))
     tools[item.id] = tool({
       description: item.description,
@@ -381,7 +393,9 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
     })
   }
 
-  for (const [key, item] of Object.entries(yield* mcp.tools())) {
+  if (codeMode) return tools
+
+  for (const [key, item] of Object.entries(mcpTools)) {
     const execute = item.execute
     if (!execute) continue
 
@@ -392,29 +406,19 @@ export const resolve = Effect.fn("SessionTools.resolve")(function* (input: {
       run.promise(
         Effect.gen(function* () {
           const ctx = context(args, opts)
-          yield* plugin.trigger(
-            "tool.execute.before",
-            { tool: key, sessionID: ctx.sessionID, callID: opts.toolCallId },
-            { args },
-          )
-          const result: Awaited<ReturnType<NonNullable<typeof execute>>> = yield* Effect.gen(function* () {
-            yield* ctx.ask({ permission: key, metadata: {}, patterns: ["*"], always: ["*"] })
-            return yield* Effect.promise(() => execute(args, opts))
-          }).pipe(
-            Effect.withSpan("Tool.execute", {
-              attributes: {
-                "tool.name": key,
-                "tool.call_id": opts.toolCallId,
-                "session.id": ctx.sessionID,
-                "message.id": input.processor.message.id,
-              },
-            }),
-          )
-          yield* plugin.trigger(
-            "tool.execute.after",
-            { tool: key, sessionID: ctx.sessionID, callID: opts.toolCallId, args },
-            result,
-          )
+          // Shared MCP middle (before hook → permission ask → Tool.execute span →
+          // dispatch → after hook); this caller keeps the model-facing shaping edge below.
+          const result: Awaited<ReturnType<NonNullable<typeof execute>>> = yield* McpInvoke.invoke({
+            plugin,
+            key,
+            execute,
+            args,
+            callID: opts.toolCallId,
+            options: opts,
+            sessionID: ctx.sessionID,
+            messageID: input.processor.message.id,
+            ask: ctx.ask,
+          })
 
           const textParts: string[] = []
           const attachments: Omit<SessionV1.FilePart, "id" | "sessionID" | "messageID">[] = []

packages/opencode/src/tool/code-mode.ts

@@ -0,0 +1,428 @@
+import * as Tool from "./tool"
+import type { Tool as AITool } from "ai"
+import type { Tool as MCPToolDef } from "@modelcontextprotocol/sdk/types.js"
+import { Cause, Effect, Schema } from "effect"
+import {
+  CodeMode,
+  Tool as SandboxTool,
+  toolError,
+  type ExecuteResult,
+  type JsonSchema,
+  type ToolDefinition,
+} from "@opencode-ai/codemode"
+import { MCP } from "@/mcp"
+import { McpCatalog } from "@/mcp/catalog"
+import { McpInvoke } from "@/mcp/invoke"
+import { Agent } from "@/agent/agent"
+import { Session } from "@/session/session"
+import { Permission } from "@/permission"
+import { Plugin } from "@/plugin"
+
+export const CODE_MODE_TOOL = "execute"
+
+// OpenCode sets NO execution limits: no timeout, no tool-call cap, and no CodeMode output
+// truncation. Cancelling the tool call aborts `ctx.abort`, which wins the race below and
+// interrupts the execution fiber — structured concurrency takes the program and its
+// in-flight child calls down with it; every child call is permission-gated anyway. Output
+// bounding is OpenCode's native tool-output truncation (Tool.define's shared wrapper),
+// which applies to `execute` like any other tool and dumps the full output to a file when
+// it triggers.
+
+// The static base description. The full usage guide and the grouped, permission-filtered
+// tool catalog are appended per agent by the registry (`describeCodeMode`, the same
+// composition point `describeTask` uses), so `plugin.trigger("tool.definition")` sees this
+// base first, exactly like the task tool.
+const DESCRIPTION = [
+  "Execute a JavaScript/TypeScript program that orchestrates the connected MCP tools inside a confined runtime.",
+  "The full usage guide and the catalog of available tools follow below.",
+].join("\n")
+
+export const Parameters = Schema.Struct({
+  code: Schema.String.annotate({
+    description: [
+      "JavaScript source to execute.",
+      "Inside CodeMode, `tools` contains only the MCP/CodeMode tools listed in this execute tool's description; top-level opencode tools like bash, read, or lsp are not available unless listed there.",
+      "Call available tools using the exact signatures shown in this execute tool's description, compose the results, and `return` the final value.",
+    ].join(" "),
+  }),
+})
+
+/** One child tool call, surfaced live so the UI can render a per-call line that
+ *  updates as the program runs. `tool` is the dotted path (e.g. `github.create_issue`). */
+export type CallEntry = { tool: string; status: "running" | "completed" | "error"; input?: Record<string, unknown> }
+
+type Metadata = {
+  toolCalls: CallEntry[]
+  error?: boolean
+}
+
+/**
+ * A tool-result attachment: identical to a session `FilePart` (minus the ids) and
+ * carrying the actual bytes (`url`, often a base64 `data:` URL), so it lowers 1:1 into
+ * `Tool.ExecuteResult.attachments`. Attachments never enter the sandbox — media stripped
+ * from child tool results is accumulated host-side and returned on the outer `execute`
+ * result, where the existing attachment plumbing turns it into visible images/files.
+ */
+export type Attachment = NonNullable<Tool.ExecuteResult["attachments"]>[number]
+
+/** One MCP tool in the grouped catalog: the flat `server_tool` key split into its
+ *  namespace (`server`) and local name, with the raw JSON Schemas used for rendering. */
+export type CatalogEntry = {
+  path: string
+  key: string
+  server: string
+  local: string
+  description: string
+  tool: AITool
+  inputSchema: JsonSchema
+  outputSchema?: JsonSchema
+}
+
+/** Render-only cast: MCP definitions carry JSON Schema documents already. */
+const toJsonSchema = (schema: unknown): JsonSchema => schema as JsonSchema
+
+/** The input schema for entries without a cached MCP definition, recovered from the
+ *  ai-sdk tool when possible so signatures stay informative. */
+function fallbackInputSchema(tool: AITool): JsonSchema {
+  const schema = (tool.inputSchema as { jsonSchema?: unknown } | undefined)?.jsonSchema
+  if (schema && typeof schema === "object") return toJsonSchema(schema)
+  return { type: "object", properties: {} }
+}
+
+/**
+ * Group the flat `server_tool` catalog into per-server namespaces. `servers` are
+ * the sanitized MCP client names; the longest matching prefix wins so a server
+ * named `a_b` beats `a` for the key `a_b_tool`. `mcpDefs` carries the raw MCP
+ * definitions (keyed identically) so each entry retains its original
+ * `inputSchema`/`outputSchema` for signature rendering.
+ */
+export function groupByServer(
+  mcpTools: Record<string, AITool>,
+  servers: readonly string[],
+  mcpDefs: Record<string, MCPToolDef> = {},
+): Map<string, CatalogEntry[]> {
+  const byLongest = [...servers].sort((a, b) => b.length - a.length)
+  const groups = new Map<string, CatalogEntry[]>()
+  for (const key of Object.keys(mcpTools).sort((a, b) => a.localeCompare(b))) {
+    const server = byLongest.find((name) => key.startsWith(name + "_")) ?? (key.includes("_") ? key.slice(0, key.indexOf("_")) : key)
+    const local = server && key.startsWith(server + "_") ? key.slice(server.length + 1) : key
+    const def = mcpDefs[key]
+    const entry: CatalogEntry = {
+      path: `${server}.${local}`,
+      key,
+      server,
+      local,
+      description: mcpTools[key]!.description ?? def?.description ?? "",
+      tool: mcpTools[key]!,
+      inputSchema: def?.inputSchema ? toJsonSchema(def.inputSchema) : fallbackInputSchema(mcpTools[key]!),
+      ...(def?.outputSchema ? { outputSchema: toJsonSchema(def.outputSchema) } : {}),
+    }
+    groups.set(server, [...(groups.get(server) ?? []), entry])
+  }
+  return groups
+}
+
+/** The executable catalog for a (already permission-filtered) MCP tool set: grouped
+ *  entries, minus any without an ai-sdk execute function. */
+export function buildCatalog(
+  mcpTools: Record<string, AITool>,
+  mcpDefs: Record<string, MCPToolDef>,
+  servers: readonly string[],
+): CatalogEntry[] {
+  return [...groupByServer(mcpTools, servers, mcpDefs).values()].flat().filter((entry) => entry.tool.execute !== undefined)
+}
+
+/**
+ * The model-facing usage guide plus grouped catalog for the given MCP tool set: the
+ * CodeMode instructions for this tool tree (syntax guide + tool signatures, or the
+ * namespace overview + search for large catalogs). Callers pass an already
+ * permission-filtered tool set — hard-denied tools never enter the catalog. The preview
+ * tree's runs are placeholders — rendering never invokes them.
+ */
+export function catalogInstructions(
+  mcpTools: Record<string, AITool>,
+  mcpDefs: Record<string, MCPToolDef>,
+  servers: readonly string[],
+): string {
+  const catalog = buildCatalog(mcpTools, mcpDefs, servers)
+  return CodeMode.make({
+    tools: toolTree(catalog, () => () => Effect.fail(toolError("Tool preview is not executable."))),
+  }).instructions()
+}
+
+function displayInput(input: unknown): Record<string, unknown> | undefined {
+  if (input === null || input === undefined) return
+  if (typeof input === "object" && !Array.isArray(input)) {
+    const value = input as Record<string, unknown>
+    if (Object.keys(value).length > 0) return value
+    return
+  }
+  return { input }
+}
+
+const lastSegment = (uri: string) => {
+  const trimmed = uri.split(/[?#]/, 1)[0]!.replace(/\/+$/, "")
+  const segment = trimmed.slice(trimmed.lastIndexOf("/") + 1)
+  return segment.length > 0 ? segment : undefined
+}
+
+const dataUrl = (mime: string, base64: string) => `data:${mime};base64,${base64}`
+
+/** The stand-in payload for a media-only tool result, so the program knows the call
+ *  succeeded even though the media itself never enters the sandbox. */
+const mediaMarker = (files: number, images: number) => {
+  const noun = files === images ? "image" : "file"
+  return `[${files} ${noun}${files === 1 ? "" : "s"} attached to the result]`
+}
+
+/**
+ * Reduce a raw MCP tool result to the value the sandbox sees. Structured content is
+ * preferred; otherwise text blocks are joined. Media blocks (image/audio/resource
+ * blob/resource_link) NEVER enter the sandbox: they are stripped into `collect`, the
+ * per-execution attachment accumulator, and a tool that returned ONLY media yields a
+ * small text marker instead. Lenient — never throws on unexpected shapes.
+ */
+export function toSandboxResult(raw: unknown, collect: (attachment: Attachment) => void): unknown {
+  if (raw === null || typeof raw !== "object") return raw
+  const record = raw as { structuredContent?: unknown; content?: unknown }
+  const content = Array.isArray(record.content) ? record.content : []
+  const text: string[] = []
+  let files = 0
+  let images = 0
+  const push = (attachment: Attachment) => {
+    files += 1
+    if (attachment.mime.startsWith("image/")) images += 1
+    collect(attachment)
+  }
+  for (const item of content) {
+    if (!item || typeof item !== "object") continue
+    const block = item as Record<string, unknown>
+    switch (block.type) {
+      case "text":
+        if (typeof block.text === "string") text.push(block.text)
+        break
+      case "image":
+      case "audio":
+        if (typeof block.data === "string" && typeof block.mimeType === "string") {
+          push({ type: "file", mime: block.mimeType, url: dataUrl(block.mimeType, block.data) })
+        }
+        break
+      case "resource": {
+        const res = block.resource as Record<string, unknown> | undefined
+        if (res && typeof res === "object") {
+          const mime = typeof res.mimeType === "string" ? res.mimeType : "application/octet-stream"
+          const uri = typeof res.uri === "string" ? res.uri : undefined
+          if (typeof res.blob === "string") {
+            push({ type: "file", mime, url: dataUrl(mime, res.blob), filename: uri ? lastSegment(uri) : undefined })
+          } else if (typeof res.text === "string") {
+            text.push(res.text)
+          }
+        }
+        break
+      }
+      case "resource_link":
+        if (typeof block.uri === "string") {
+          push({
+            type: "file",
+            mime: typeof block.mimeType === "string" ? block.mimeType : "application/octet-stream",
+            url: block.uri,
+            filename: typeof block.name === "string" ? block.name : lastSegment(block.uri),
+          })
+        }
+        break
+    }
+  }
+
+  if (record.structuredContent !== undefined && record.structuredContent !== null) return record.structuredContent
+  if (text.length > 0) return text.join("\n")
+  if (files > 0) return mediaMarker(files, images)
+  if (Array.isArray(record.content)) return null // MCP-shaped result with nothing extractable
+  return raw
+}
+
+/**
+ * Append captured `console.*` output to the model-facing text as a trailing `Logs:` section,
+ * so a program's diagnostics ride back alongside its result — on success AND on error.
+ * Returns the text unchanged when nothing was logged. This is the sandbox's only
+ * stdout-like channel — it goes to the model, not the user.
+ */
+export function withLogs(output: string, logs: ReadonlyArray<string> = []): string {
+  if (logs.length === 0) return output
+  const section = "Logs:\n" + logs.join("\n")
+  return output.length > 0 ? `${output}\n\n${section}` : section
+}
+
+/** Coerce the program's return value to model-facing text without ever failing on shape. */
+export function formatValue(value: unknown): string {
+  if (typeof value === "string") return value
+  if (value === undefined) return "undefined"
+  try {
+    return JSON.stringify(value, null, 2) ?? String(value)
+  } catch {
+    return String(value)
+  }
+}
+
+type Run = (input: unknown) => Effect.Effect<unknown, unknown>
+
+/** Build the `tools.<server>.<tool>` tree CodeMode executes against, one
+ *  `Tool.make` definition per MCP tool with its render-only JSON Schemas. */
+function toolTree(catalog: readonly CatalogEntry[], run: (entry: CatalogEntry) => Run) {
+  const tree: Record<string, Record<string, ToolDefinition>> = {}
+  for (const entry of catalog) {
+    const namespace = (tree[entry.server] ??= {})
+    namespace[entry.local] = SandboxTool.make({
+      description: entry.description,
+      input: entry.inputSchema,
+      output: entry.outputSchema,
+      run: run(entry),
+    })
+  }
+  return tree
+}
+
+/** Failures inside a child call — plugin hook failures, permission denials, and tool
+ *  failures alike — become safe, catchable in-program errors via toolError, so a
+ *  program can try/catch one call without the whole execution dying. Interruption
+ *  (user cancel) keeps propagating as interruption. */
+const toCatchable = <A, E, R>(effect: Effect.Effect<A, E, R>) =>
+  effect.pipe(
+    Effect.catchCause((cause) => {
+      if (Cause.hasInterruptsOnly(cause)) return Effect.interrupt
+      const error = Cause.squash(cause)
+      return Effect.fail(toolError(error instanceof Error ? error.message : String(error), error))
+    }),
+  )
+
+export const CodeModeTool = Tool.define(
+  CODE_MODE_TOOL,
+  Effect.gen(function* () {
+    const mcp = yield* MCP.Service
+    const agents = yield* Agent.Service
+    const sessions = yield* Session.Service
+    const plugin = yield* Plugin.Service
+
+    const init: Tool.DefWithoutID<typeof Parameters, Metadata> = {
+      description: DESCRIPTION,
+      parameters: Parameters,
+      execute: Effect.fn("CodeMode.execute")(function* (params, ctx) {
+        // Already cancelled: don't start the program at all. (The mid-flight case is the
+        // race below; racing alone would still let the program run its first steps.)
+        if (ctx.abort.aborted) {
+          return {
+            title: CODE_MODE_TOOL,
+            metadata: { toolCalls: [], error: true },
+            output: "Execution cancelled.",
+          } satisfies Tool.ExecuteResult<Metadata>
+        }
+        // A fresh MCP snapshot per execution, so the runtime tracks live tool-list
+        // changes, filtered with the same merged agent+session ruleset that gates
+        // `ctx.ask` (see SessionTools.context). A hard-denied tool never enters the
+        // tree, so it is not dispatchable even if the model guesses its name — the
+        // program gets the normal unknown-tool diagnostic, not a permission error.
+        const agent = yield* agents.get(ctx.agent)
+        const session = yield* sessions.get(ctx.sessionID).pipe(Effect.orDie)
+        const ruleset = Permission.merge(agent.permission, session.permission ?? [])
+        const mcpTools = Permission.visibleTools(yield* mcp.tools(), ruleset)
+        const servers = Object.keys(yield* mcp.clients()).map(McpCatalog.sanitize)
+        const catalog = buildCatalog(mcpTools, yield* mcp.defs(), servers)
+
+        const calls: CallEntry[] = []
+        // Media stripped from child tool results accumulates here for the life of the
+        // call; the bytes never enter the sandbox (see toSandboxResult).
+        const attachments: Attachment[] = []
+        const collect = (attachment: Attachment) => void attachments.push(attachment)
+        // Stream the current call list to the UI. Sent on every status change so the
+        // tool part shows each child call appearing and resolving while the program runs.
+        const publish = () => ctx.metadata({ title: CODE_MODE_TOOL, metadata: { toolCalls: calls.map((c) => ({ ...c })) } })
+
+        // One CodeMode tool per MCP tool, running the same shared middle as legacy
+        // per-tool registration (McpInvoke.invoke: plugin before hook → permission
+        // ask → Tool.execute span → dispatch through the ai-sdk wrapper, which owns
+        // callTool timeouts/progress and turns an MCP isError into a thrown Error →
+        // plugin after hook), so plugins observe child calls too. Each child gets a
+        // synthetic hook/span callID `${parentCallID}/${n}` (per-execution counter,
+        // opaque — nothing parses it); the ai-sdk toolCallId is unchanged. Failures —
+        // hook, denial, or tool — fail only that child call as a safe, catchable
+        // in-program error (toCatchable); the raw result is then shaped for the sandbox.
+        let childCalls = 0
+        const callTool = (entry: CatalogEntry) => (input: unknown) =>
+          toCatchable(
+            Effect.gen(function* () {
+              childCalls += 1
+              const raw = yield* McpInvoke.invoke({
+                plugin,
+                key: entry.key,
+                execute: entry.tool.execute!,
+                args: input ?? {},
+                callID: `${ctx.callID ?? entry.key}/${childCalls}`,
+                options: { toolCallId: ctx.callID ?? entry.key, abortSignal: ctx.abort, messages: [] },
+                sessionID: ctx.sessionID,
+                messageID: ctx.messageID,
+                ask: ctx.ask,
+              })
+              return toSandboxResult(raw, collect)
+            }),
+          )
+
+        const runtime = CodeMode.make({
+          tools: toolTree(catalog, callTool),
+          onToolCallStart: ({ index, name, input }) =>
+            Effect.suspend(() => {
+              const shown = displayInput(input)
+              calls[index] = { tool: name, status: "running", ...(shown ? { input: shown } : {}) }
+              return publish()
+            }),
+          onToolCallEnd: ({ index, outcome }) =>
+            Effect.suspend(() => {
+              const current = calls[index]
+              if (current) calls[index] = { ...current, status: outcome === "success" ? "completed" : "error" }
+              return publish()
+            }),
+        })
+
+        // The shared tool runner does not wire ctx.abort to fiber interruption (it runs
+        // tools via Effect.runPromise with no abort handling), so without this race the
+        // program would keep running after the user cancels. The abort signal winning the
+        // race interrupts the execution fiber; the cancelled result keeps the runner's
+        // post-abort bookkeeping (completeToolCall) on its normal path.
+        const cancelled = Effect.callback<ExecuteResult>((resume) => {
+          const onAbort = () =>
+            resume(
+              Effect.succeed<ExecuteResult>({
+                ok: false,
+                error: { kind: "ExecutionFailure", message: "Execution cancelled." },
+                toolCalls: calls.map((call) => ({ name: call.tool })),
+              }),
+            )
+          if (ctx.abort.aborted) return onAbort()
+          ctx.abort.addEventListener("abort", onAbort, { once: true })
+          return Effect.sync(() => ctx.abort.removeEventListener("abort", onAbort))
+        })
+
+        const result = yield* Effect.raceFirst(runtime.execute(params.code), cancelled)
+        const logs = result.logs ?? []
+        const attached = attachments.length > 0 ? { attachments } : {}
+
+        if (result.ok) {
+          return {
+            title: CODE_MODE_TOOL,
+            metadata: { toolCalls: calls },
+            output: withLogs(formatValue(result.value), logs),
+            ...attached,
+          } satisfies Tool.ExecuteResult<Metadata>
+        }
+        // Diagnostics may carry suggestions (e.g. pointing an unknown tool at
+        // discovery); append the ones the message doesn't already contain.
+        const hints = (result.error.suggestions ?? []).filter((hint) => !result.error.message.includes(hint))
+        return {
+          title: CODE_MODE_TOOL,
+          metadata: { toolCalls: calls, error: true },
+          output: withLogs([result.error.message, ...hints].join("\n"), logs),
+          ...attached,
+        } satisfies Tool.ExecuteResult<Metadata>
+      }),
+    }
+    return init
+  }),
+)

packages/opencode/src/tool/registry.ts

@@ -26,6 +26,9 @@ import { Plugin } from "../plugin"
 import { Provider } from "@/provider/provider"
 
 import { WebSearchTool } from "./websearch"
+import { CodeModeTool, catalogInstructions } from "./code-mode"
+import { MCP } from "@/mcp"
+import { McpCatalog } from "@/mcp/catalog"
 import { LspTool } from "./lsp"
 import * as Truncate from "./truncate"
 import { ApplyPatchTool } from "./apply_patch"
@@ -51,6 +54,7 @@ import { BackgroundJob } from "@/background/job"
 import { RuntimeFlags } from "@/effect/runtime-flags"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { ModelV2 } from "@opencode-ai/core/model"
+import type { PermissionV1 } from "@opencode-ai/core/v1/permission"
 
 export function webSearchEnabled(providerID: ProviderV2.ID, flags = { exa: false, parallel: false }) {
   return providerID === ProviderV2.ID.opencode || flags.exa || flags.parallel
@@ -74,6 +78,7 @@ export interface Interface {
     providerID: ProviderV2.ID
     modelID: ModelV2.ID
     agent: Agent.Info
+    permission?: PermissionV1.Ruleset
   }) => Effect.Effect<Tool.Def[]>
 }
 
@@ -87,6 +92,7 @@ const layer = Layer.effect(
     const agents = yield* Agent.Service
     const truncate = yield* Truncate.Service
     const flags = yield* RuntimeFlags.Service
+    const mcp = yield* MCP.Service
 
     const invalid = yield* InvalidTool
     const task = yield* TaskTool
@@ -104,6 +110,7 @@ const layer = Layer.effect(
     const greptool = yield* GrepTool
     const patchtool = yield* ApplyPatchTool
     const skilltool = yield* SkillTool
+    const codemode = yield* CodeModeTool
     const agent = yield* Agent.Service
 
     const state = yield* InstanceState.make<State>(
@@ -211,6 +218,7 @@ const layer = Layer.effect(
           question: Tool.init(question),
           lsp: Tool.init(lsptool),
           plan: Tool.init(plan),
+          codemode: Tool.init(codemode),
         })
 
         return {
@@ -232,6 +240,7 @@ const layer = Layer.effect(
             tool.patch,
             ...(flags.experimentalLspTool ? [tool.lsp] : []),
             ...(flags.experimentalPlanMode && flags.client === "cli" ? [tool.plan] : []),
+            ...(flags.experimentalCodeMode ? [tool.codemode] : []),
           ],
           task: tool.task,
           read: tool.read,
@@ -263,11 +272,25 @@ const layer = Layer.effect(
       return ["Available agent types and the tools they have access to:", description].join("\n")
     })
 
+    // The grouped MCP-tool catalog appended to the code-mode base description, built
+    // fresh per turn so it tracks live tool-list changes. Hard-denied tools (the shared
+    // Permission.visibleTools predicate over the agent's ruleset) never enter the
+    // catalog, its inlined signatures, or the in-program search index.
+    const describeCodeMode = Effect.fn("ToolRegistry.describeCodeMode")(function* (agent: Agent.Info, permission?: PermissionV1.Ruleset) {
+      const visible = Permission.visibleTools(yield* mcp.tools(), Permission.merge(agent.permission, permission ?? []))
+      const servers = Object.keys(yield* mcp.clients()).map(McpCatalog.sanitize)
+      return catalogInstructions(visible, yield* mcp.defs(), servers)
+    })
+
     const tools: Interface["tools"] = Effect.fn("ToolRegistry.tools")(function* (input) {
+      // Consulted once before the synchronous filter: code mode registers only when the
+      // experimental flag is on AND at least one MCP tool is connected.
+      const mcpToolCount = flags.experimentalCodeMode ? Object.keys(yield* mcp.tools()).length : 0
       const filtered = (yield* all()).filter((tool) => {
         if (tool.id === WebSearchTool.id) {
           return webSearchEnabled(input.providerID, { exa: flags.enableExa, parallel: flags.enableParallel })
         }
+        if (tool.id === CodeModeTool.id) return flags.experimentalCodeMode && mcpToolCount > 0
 
         const usePatch =
           input.modelID.includes("gpt-") && !input.modelID.includes("oss") && !input.modelID.includes("gpt-4")
@@ -292,7 +315,11 @@ const layer = Layer.effect(
               : undefined
           return {
             id: tool.id,
-            description: [output.description, tool.id === TaskTool.id ? yield* describeTask(input.agent) : undefined]
+            description: [
+              output.description,
+              tool.id === TaskTool.id ? yield* describeTask(input.agent) : undefined,
+              tool.id === CodeModeTool.id ? yield* describeCodeMode(input.agent, input.permission) : undefined,
+            ]
               .filter(Boolean)
               .join("\n"),
             parameters: output.parameters,
@@ -314,6 +341,7 @@ const layer = Layer.effect(
   }),
 )
 
+
 function isZodType(value: unknown): value is z.ZodType {
   return typeof value === "object" && value !== null && "_zod" in value
 }
@@ -406,6 +434,7 @@ export const node = LayerNode.make({
     LSP.node,
     Instruction.node,
     FSUtil.node,
+    MCP.node,
     EventV2Bridge.node,
     httpClient,
     CrossSpawnSpawner.node,

packages/opencode/test/session/prompt.test.ts

@@ -117,6 +117,7 @@ function makeMcp(instructions: MCP.ServerInstructions[] = []) {
       clients: () => Effect.succeed({}),
       instructions: () => Effect.succeed(instructions),
       tools: () => Effect.succeed({}),
+      defs: () => Effect.succeed({}),
       prompts: () => Effect.succeed({}),
       resources: () => Effect.succeed({}),
       resourceTemplates: () => Effect.succeed({}),

packages/opencode/test/session/snapshot-tool-race.test.ts

@@ -39,6 +39,7 @@ const mcp = Layer.succeed(
     clients: () => Effect.succeed({}),
     instructions: () => Effect.succeed([]),
     tools: () => Effect.succeed({}),
+    defs: () => Effect.succeed({}),
     prompts: () => Effect.succeed({}),
     resources: () => Effect.succeed({}),
     resourceTemplates: () => Effect.succeed({}),

packages/opencode/test/session/tools.test.ts

@@ -0,0 +1,164 @@
+import { afterEach, describe, expect } from "bun:test"
+import path from "path"
+import { Effect, Layer } from "effect"
+import { LayerNode } from "@opencode-ai/core/effect/layer-node"
+import { SessionTools } from "@/session/tools"
+import { ToolRegistry } from "@/tool/registry"
+import { Agent } from "@/agent/agent"
+import { Config } from "@/config/config"
+import { MCP } from "@/mcp"
+import { McpCatalog } from "@/mcp/catalog"
+import { Permission } from "@/permission"
+import { Plugin } from "@/plugin"
+import * as Truncate from "@/tool/truncate"
+import { RuntimeFlags } from "@/effect/runtime-flags"
+import { InstanceState } from "@/effect/instance-state"
+import { MessageID, SessionID } from "@/session/schema"
+import { disposeAllInstances } from "../fixture/fixture"
+import { testEffect } from "../lib/effect"
+import { TestConfig } from "../fixture/config"
+import type { Tool as AITool } from "ai"
+
+const configLayer = TestConfig.layer({
+  directories: () => InstanceState.directory.pipe(Effect.map((dir) => [path.join(dir, ".opencode")])),
+})
+
+// Fake MCP.Service built through the same `convertTool` path the real service uses,
+// so the raw registration loop dispatches through a genuine ai-sdk execute. The fake
+// client answers every call with a small text result.
+function fakeMcpLayer(tools: Record<string, { description: string }>) {
+  const client = { callTool: async () => ({ content: [{ type: "text", text: "ok" }] }) }
+  const converted: Record<string, AITool> = Object.fromEntries(
+    Object.entries(tools).map(([key, def]) => [
+      key,
+      McpCatalog.convertTool(
+        {
+          name: key,
+          description: def.description,
+          inputSchema: { type: "object", properties: {} },
+        } as any,
+        client as any,
+      ),
+    ]),
+  )
+  return Layer.mock(MCP.Service, {
+    tools: () => Effect.succeed(converted),
+    defs: () => Effect.succeed({}),
+    clients: () => Effect.succeed({ github: { getServerCapabilities: () => undefined } } as any),
+  })
+}
+
+const mcpToolsLayer = fakeMcpLayer({
+  github_create_issue: { description: "Create an issue" },
+  github_list_issues: { description: "List issues" },
+})
+
+const root = LayerNode.group([ToolRegistry.node, Agent.node, MCP.node, RuntimeFlags.node])
+const withCodeMode = testEffect(
+  LayerNode.compile(root, [
+    [Config.node, configLayer],
+    [RuntimeFlags.node, RuntimeFlags.layer({ experimentalCodeMode: true })],
+    [MCP.node, mcpToolsLayer],
+  ]),
+)
+const withFlagOff = testEffect(
+  LayerNode.compile(root, [
+    [Config.node, configLayer],
+    [RuntimeFlags.node, RuntimeFlags.layer()],
+    [MCP.node, mcpToolsLayer],
+  ]),
+)
+
+// Resolve the session tool record with the smallest honest stand-ins for the pieces
+// resolve reads: a fabricated model (only providerID/api.id are consulted by the
+// schema transform for these fixtures), a pass-through Truncate, an always-allow
+// Permission, and an optionally-observing Plugin.trigger. Registry, MCP, and flags
+// come from the compiled instance context.
+function resolveTools(trigger?: Plugin.Interface["trigger"]) {
+  return Effect.gen(function* () {
+    const agents = yield* Agent.Service
+    const agent = yield* agents.defaultInfo()
+    return yield* SessionTools.resolve({
+      agent,
+      model: { providerID: "opencode", api: { id: "test" } } as any,
+      session: { id: SessionID.make("ses_session-tools"), permission: [] } as any,
+      processor: {
+        message: { id: MessageID.make("msg_session-tools") } as any,
+        updateToolCall: () => Effect.succeed(undefined),
+        completeToolCall: () => Effect.void,
+      },
+      bypassAgentCheck: false,
+      messages: [],
+      promptOps: {} as any,
+    })
+  }).pipe(
+    Effect.provide(
+      Layer.mergeAll(
+        Layer.mock(Permission.Service, { ask: () => Effect.void }),
+        Layer.mock(Plugin.Service, {
+          trigger:
+            trigger ?? (((_name, _input, output) => Effect.succeed(output)) as Plugin.Interface["trigger"]),
+        }),
+        Layer.mock(Truncate.Service, {
+          output: (text: string) => Effect.succeed({ content: text, truncated: false as const }),
+        }),
+      ),
+    ),
+  )
+}
+
+afterEach(async () => {
+  await disposeAllInstances()
+})
+
+describe("session.tools resolve", () => {
+  withCodeMode.instance("code mode suppresses raw per-MCP registration behind the execute tool", () =>
+    Effect.gen(function* () {
+      const tools = yield* resolveTools()
+      const ids = Object.keys(tools)
+      expect(ids).toContain("execute")
+      expect(ids).not.toContain("github_create_issue")
+      expect(ids).not.toContain("github_list_issues")
+    }),
+  )
+
+  withFlagOff.instance("without code mode the raw MCP tools register and execute is absent", () =>
+    Effect.gen(function* () {
+      const tools = yield* resolveTools()
+      const ids = Object.keys(tools)
+      expect(ids).not.toContain("execute")
+      expect(ids).toContain("github_create_issue")
+      expect(ids).toContain("github_list_issues")
+    }),
+  )
+
+  withFlagOff.instance("legacy raw MCP execution fires plugin hooks keyed by the ai-sdk toolCallId", () =>
+    Effect.gen(function* () {
+      const events: { name: string; input: any; output: any }[] = []
+      const trigger = ((name: unknown, input: unknown, output: unknown) =>
+        Effect.sync(() => {
+          events.push({ name: name as string, input, output })
+          return output
+        })) as Plugin.Interface["trigger"]
+      const tools = yield* resolveTools(trigger)
+      const raw = tools["github_create_issue"]!
+      const result = yield* Effect.promise(() =>
+        Promise.resolve(
+          raw.execute!(
+            { title: "x" },
+            { toolCallId: "call_legacy", abortSignal: new AbortController().signal, messages: [] },
+          ),
+        ),
+      )
+
+      expect((result as any).output).toBe("ok")
+      expect(events.map((e) => [e.name, e.input.tool, e.input.callID])).toEqual([
+        ["tool.execute.before", "github_create_issue", "call_legacy"],
+        ["tool.execute.after", "github_create_issue", "call_legacy"],
+      ])
+      expect(events[0]!.output).toEqual({ args: { title: "x" } })
+      // The after hook receives the raw MCP result, before model-facing shaping.
+      expect(events[1]!.output).toMatchObject({ content: [{ type: "text", text: "ok" }] })
+    }),
+  )
+})

packages/opencode/test/tool/code-mode-integration.test.ts

@@ -0,0 +1,354 @@
+import { beforeAll, describe, expect, test } from "bun:test"
+import { CodeModeTool, catalogInstructions } from "@/tool/code-mode"
+import { McpCatalog } from "@/mcp/catalog"
+import { Agent } from "@/agent/agent"
+import { MCP } from "@/mcp"
+import { Plugin } from "@/plugin"
+import { Session } from "@/session/session"
+import { Tool } from "@/tool/tool"
+import * as Truncate from "@/tool/truncate"
+import { MessageID, SessionID } from "@/session/schema"
+import { Server } from "@modelcontextprotocol/sdk/server/index.js"
+import { InMemoryTransport } from "@modelcontextprotocol/sdk/inMemory.js"
+import type { Client } from "@modelcontextprotocol/sdk/client/index.js"
+import {
+  CallToolRequestSchema,
+  LATEST_PROTOCOL_VERSION,
+  ListToolsRequestSchema,
+  type Tool as MCPToolDef,
+} from "@modelcontextprotocol/sdk/types.js"
+import type { Tool as AITool } from "ai"
+import { Effect, Layer } from "effect"
+
+// A 1x1 transparent PNG, base64-encoded, used to exercise image attachments.
+const PNG =
+  "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYPhfDwAChwGA60e6kgAAAABJRU5ErkJggg=="
+
+const SERVER = "fixtures"
+
+const ctx: Tool.Context = {
+  sessionID: SessionID.make("ses_code-mode-int"),
+  messageID: MessageID.make("msg_code-mode-int"),
+  agent: "build",
+  abort: new AbortController().signal,
+  callID: "call_code_mode_int",
+  messages: [],
+  metadata: () => Effect.void,
+  ask: () => Effect.void,
+}
+
+/**
+ * A minimal JSON-RPC MCP client speaking the real protocol over the in-memory transport.
+ * Deliberately NOT the SDK `Client`: `test/mcp/lifecycle.test.ts` (and friends) replace
+ * `@modelcontextprotocol/sdk/client/index.js` via bun's `mock.module`, which is
+ * process-global and irreversible — in a full `bun test` run (CI) any later import of the
+ * SDK Client gets the mock, whose `listTools` returns a canned `test_tool`. Speaking raw
+ * JSON-RPC keeps this suite's "real server, real transport, real protocol" property while
+ * being immune to that contamination. Only the surface `convertTool`/this file use is
+ * implemented: connect handshake, tools/list, tools/call.
+ */
+class RawJsonRpcClient {
+  private nextId = 1
+  private pending = new Map<number, { resolve: (value: any) => void; reject: (error: Error) => void }>()
+
+  constructor(private transport: InMemoryTransport) {}
+
+  async connect() {
+    this.transport.onmessage = (message) => {
+      const msg = message as { id?: number; result?: unknown; error?: { message: string } }
+      if (msg.id === undefined) return // notifications/requests from the server are not needed here
+      const entry = this.pending.get(msg.id)
+      if (!entry) return
+      this.pending.delete(msg.id)
+      if (msg.error) entry.reject(new Error(msg.error.message))
+      else entry.resolve(msg.result)
+    }
+    await this.transport.start()
+    await this.request("initialize", {
+      protocolVersion: LATEST_PROTOCOL_VERSION,
+      capabilities: {},
+      clientInfo: { name: "test-client", version: "1.0.0" },
+    })
+    await this.transport.send({ jsonrpc: "2.0", method: "notifications/initialized" })
+  }
+
+  private request(method: string, params: unknown): Promise<any> {
+    const id = this.nextId++
+    const result = new Promise((resolve, reject) => this.pending.set(id, { resolve, reject }))
+    void this.transport.send({ jsonrpc: "2.0", id, method, params } as never)
+    return result
+  }
+
+  listTools() {
+    return this.request("tools/list", {})
+  }
+
+  /** The `convertTool` surface: schema/options (timeouts, progress) are SDK-client
+   *  concerns and are ignored here — the server never sees them. */
+  callTool(params: { name: string; arguments?: Record<string, unknown> }, _schema?: unknown, _options?: unknown) {
+    return this.request("tools/call", params)
+  }
+}
+
+// A real MCP server, exposed over an in-memory transport, with a representative mix
+// of tools: plain text, structured data (with an outputSchema), an image, and a
+// failing tool. Tools are defined with raw JSON Schema so outputSchema is exact.
+const TOOL_DEFS: MCPToolDef[] = [
+  {
+    name: "get_text",
+    description: "Greet someone and return the greeting as text",
+    inputSchema: { type: "object", properties: { name: { type: "string" } }, required: ["name"] },
+  },
+  {
+    name: "add",
+    description: "Add two numbers and return the structured sum",
+    inputSchema: { type: "object", properties: { a: { type: "number" }, b: { type: "number" } }, required: ["a", "b"] },
+    outputSchema: { type: "object", properties: { sum: { type: "number" } }, required: ["sum"] },
+  },
+  {
+    name: "screenshot",
+    description: "Capture a screenshot and return it as an image",
+    inputSchema: { type: "object", properties: {} },
+  },
+  {
+    name: "boom",
+    description: "A tool that always fails",
+    inputSchema: { type: "object", properties: {} },
+  },
+] as MCPToolDef[]
+
+function handleCall(name: string, args: Record<string, unknown>) {
+  switch (name) {
+    case "get_text":
+      return { content: [{ type: "text", text: `hello ${args.name}` }] }
+    case "add": {
+      const sum = (args.a as number) + (args.b as number)
+      return { content: [{ type: "text", text: String(sum) }], structuredContent: { sum } }
+    }
+    case "screenshot":
+      return { content: [{ type: "image", data: PNG, mimeType: "image/png" }] }
+    case "boom":
+      return { content: [{ type: "text", text: "kaboom" }], isError: true }
+    default:
+      return { content: [{ type: "text", text: `unknown tool ${name}` }], isError: true }
+  }
+}
+
+let tool: Awaited<ReturnType<typeof buildTool>>["tool"]
+let description: string
+
+async function buildTool() {
+  const server = new Server({ name: SERVER, version: "1.0.0" }, { capabilities: { tools: {} } })
+  server.setRequestHandler(ListToolsRequestSchema, async () => ({ tools: TOOL_DEFS }))
+  server.setRequestHandler(CallToolRequestSchema, async (req) =>
+    handleCall(req.params.name, (req.params.arguments ?? {}) as Record<string, unknown>),
+  )
+
+  const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair()
+  await server.connect(serverTransport)
+  const client = new RawJsonRpcClient(clientTransport)
+  await client.connect()
+
+  const listed = (await client.listTools()).tools as MCPToolDef[]
+  const mcpTools: Record<string, AITool> = {}
+  const mcpDefs: Record<string, MCPToolDef> = {}
+  for (const def of listed) {
+    const key = McpCatalog.toolName(SERVER, def.name)
+    mcpDefs[key] = def
+    mcpTools[key] = McpCatalog.convertTool(def, client as unknown as Client)
+  }
+
+  // Truncate echoes its input so assertions read the exact program output; Agent/Session
+  // supply the (empty) permission rulesets the execute path merges; MCP serves the tools
+  // this real in-memory server listed — the same snapshot shape the live service returns.
+  const layer = Layer.mergeAll(
+    Layer.mock(Plugin.Service, {
+      trigger: (((_name: unknown, _input: unknown, output: unknown) =>
+        Effect.succeed(output)) as Plugin.Interface["trigger"]),
+    }),
+    Layer.mock(Truncate.Service, {
+      output: (text: string) => Effect.succeed({ content: text, truncated: false as const }),
+    }),
+    Layer.mock(Agent.Service, { get: () => Effect.succeed({ name: "build", permission: [] } as any) }),
+    Layer.mock(Session.Service, { get: () => Effect.succeed({ permission: [] } as any) }),
+    Layer.mock(MCP.Service, {
+      tools: () => Effect.succeed(mcpTools),
+      defs: () => Effect.succeed(mcpDefs),
+      clients: () => Effect.succeed({ [SERVER]: {} as any }),
+    }),
+  )
+  return {
+    tool: await Effect.runPromise(CodeModeTool.pipe(Effect.flatMap(Tool.init), Effect.provide(layer))),
+    // The catalog section the registry appends to the base description (describeCodeMode).
+    description: catalogInstructions(mcpTools, mcpDefs, [SERVER]),
+  }
+}
+
+const run = (code: string) => Effect.runPromise(tool.execute({ code }, ctx))
+
+beforeAll(async () => {
+  const built = await buildTool()
+  tool = built.tool
+  description = built.description
+})
+
+describe("code mode integration (real MCP server)", () => {
+  test("the appended catalog inlines full signatures with real MCP schemas", () => {
+    expect(description).toContain("Available tools (COMPLETE list")
+    expect(description).toContain("- fixtures (4 tools)")
+    expect(description).toContain(
+      "tools.fixtures.add(input: { a: number; b: number }): Promise<{ sum: number }>",
+    )
+    expect(description).toContain("tools.fixtures.get_text(input: { name: string }): Promise<unknown>")
+    expect(description).toContain("// Add two numbers and return the structured sum")
+    // Small catalog: everything is inline, so no discovery tool is advertised.
+    expect(description).not.toContain("$codemode")
+    // The workflow section is present with placeholder-only call forms.
+    expect(description).toContain("## Workflow")
+    expect(description).toContain("`const res = await tools.<namespace>.<tool>(input)`")
+    expect(description).not.toContain("total_count")
+  })
+
+  test("calls a text tool and receives its text as the native result", async () => {
+    const out = await run("const r = await tools.fixtures.get_text({ name: 'world' }); return r")
+    expect(out.output).toBe("hello world")
+    expect(out.metadata.toolCalls).toEqual([
+      { tool: "fixtures.get_text", status: "completed", input: { name: "world" } },
+    ])
+    expect(out.attachments).toBeUndefined()
+  })
+
+  test("exposes structured data natively from a tool with an outputSchema", async () => {
+    const out = await run("const r = await tools.fixtures.add({ a: 2, b: 3 }); return r.sum")
+    expect(out.output).toBe("5")
+  })
+
+  test("composes multiple structured calls and returns a plain object", async () => {
+    const out = await run(`
+      const first = await tools.fixtures.add({ a: 1, b: 2 })
+      const second = await tools.fixtures.add({ a: first.sum, b: 10 })
+      return { total: second.sum }
+    `)
+    expect(JSON.parse(out.output)).toEqual({ total: 13 })
+    expect(out.metadata.toolCalls).toEqual([
+      { tool: "fixtures.add", status: "completed", input: { a: 1, b: 2 } },
+      { tool: "fixtures.add", status: "completed", input: { a: 3, b: 10 } },
+    ])
+  })
+
+  test("an image result becomes an execute attachment and a marker in the sandbox", async () => {
+    const out = await run("return await tools.fixtures.screenshot({})")
+    expect(out.output).toBe("[1 image attached to the result]")
+    expect(out.attachments).toEqual([{ type: "file", mime: "image/png", url: `data:image/png;base64,${PNG}` }])
+  })
+
+  test("image bytes never enter the sandbox or the model-facing output", async () => {
+    const out = await run(`
+      const shot = await tools.fixtures.screenshot({})
+      return { sawMarker: typeof shot === 'string' && shot.includes('attached'), value: shot }
+    `)
+    expect(JSON.parse(out.output)).toEqual({
+      sawMarker: true,
+      value: "[1 image attached to the result]",
+    })
+    expect(out.output).not.toContain(PNG)
+    // The stripped image still arrives as a real attachment.
+    expect(out.attachments).toHaveLength(1)
+  })
+
+  test("attachments accumulate even when the program returns something else", async () => {
+    const out = await run("await tools.fixtures.screenshot({}); return 'captured'")
+    expect(out.output).toBe("captured")
+    expect(out.attachments).toHaveLength(1)
+  })
+
+  test("runs calls in parallel and accumulates every attachment", async () => {
+    const out = await run(`
+      const both = await Promise.all([tools.fixtures.screenshot({}), tools.fixtures.screenshot({})])
+      return 'two shots: ' + both.length
+    `)
+    expect(out.output).toBe("two shots: 2")
+    expect(out.attachments).toHaveLength(2)
+    expect(out.metadata.toolCalls.map((c) => c.tool)).toEqual(["fixtures.screenshot", "fixtures.screenshot"])
+  })
+
+  test("propagates an MCP isError into the program as a catchable error", async () => {
+    const out = await run("try { await tools.fixtures.boom({}) } catch (e) { return 'caught: ' + e.message }")
+    expect(out.output).toBe("caught: kaboom")
+  })
+
+  test("an uncaught MCP error surfaces as a failed execution", async () => {
+    const out = await run("await tools.fixtures.boom({}); return 'unreachable'")
+    expect(out.metadata.error).toBe(true)
+    expect(out.output).toContain("kaboom")
+  })
+
+  test("console output is captured and appended as a Logs section after the result", async () => {
+    const out = await run(`
+      console.log("looking up", { name: "world" })
+      const r = await tools.fixtures.get_text({ name: "world" })
+      console.warn("got", r)
+      return r
+    `)
+    expect(out.output).toBe('hello world\n\nLogs:\nlooking up {"name":"world"}\n[warn] got hello world')
+    expect(out.metadata.error).toBeUndefined()
+  })
+
+  test("console output is preserved on the error path", async () => {
+    const out = await run(`
+      console.log("before the throw")
+      await tools.fixtures.boom({})
+      return "unreachable"
+    `)
+    expect(out.metadata.error).toBe(true)
+    expect(out.output).toContain("kaboom")
+    expect(out.output).toContain("Logs:\nbefore the throw")
+  })
+
+  test("a program that logs nothing gets no Logs section", async () => {
+    const out = await run("return 'quiet'")
+    expect(out.output).toBe("quiet")
+    expect(out.output).not.toContain("Logs:")
+  })
+
+  test("console does not consume the tool-call metadata (logging is not a tool call)", async () => {
+    const out = await run("console.log('hi'); console.error('bye'); return 'ok'")
+    expect(out.output).toBe("ok\n\nLogs:\nhi\n[error] bye")
+    expect(out.metadata.toolCalls).toEqual([])
+  })
+
+  test("asks permission for each MCP call, keyed by the flat catalog name", async () => {
+    const asked: string[] = []
+    const permCtx: Tool.Context = { ...ctx, ask: (req: any) => Effect.sync(() => void asked.push(req.permission)) }
+    await Effect.runPromise(
+      tool.execute(
+        {
+          code: `
+            await tools.fixtures.add({ a: 1, b: 1 })
+            await tools.fixtures.get_text({ name: 'x' })
+            return 'done'
+          `,
+        },
+        permCtx,
+      ),
+    )
+    expect(asked).toEqual(["fixtures_add", "fixtures_get_text"])
+  })
+
+  test("streams running/completed metadata for child calls over a real transport", async () => {
+    const snapshots: Array<{ toolCalls: { tool: string; status: string; input?: Record<string, unknown> }[] }> = []
+    const recordingCtx: Tool.Context = {
+      ...ctx,
+      metadata: (val: any) => Effect.sync(() => void snapshots.push(val.metadata)),
+    }
+    await Effect.runPromise(
+      tool.execute({ code: "await tools.fixtures.add({ a: 1, b: 2 }); return 'done'" }, recordingCtx),
+    )
+    expect(snapshots).toContainEqual({
+      toolCalls: [{ tool: "fixtures.add", status: "running", input: { a: 1, b: 2 } }],
+    })
+    expect(snapshots).toContainEqual({
+      toolCalls: [{ tool: "fixtures.add", status: "completed", input: { a: 1, b: 2 } }],
+    })
+  })
+})

packages/opencode/test/tool/code-mode.test.ts

@@ -0,0 +1,861 @@
+import { describe, expect, test } from "bun:test"
+import {
+  CODE_MODE_TOOL,
+  CodeModeTool,
+  Parameters,
+  catalogInstructions,
+  formatValue,
+  groupByServer,
+  toSandboxResult,
+  withLogs,
+  type Attachment,
+} from "@/tool/code-mode"
+import type { Tool as MCPToolDef } from "@modelcontextprotocol/sdk/types.js"
+import type { PermissionV1 } from "@opencode-ai/core/v1/permission"
+import { Agent } from "@/agent/agent"
+import { MCP } from "@/mcp"
+import { Permission } from "@/permission"
+import { Plugin } from "@/plugin"
+import { Session } from "@/session/session"
+import { Tool } from "@/tool/tool"
+import * as Truncate from "@/tool/truncate"
+import { McpCatalog } from "@/mcp/catalog"
+import { MessageID, SessionID } from "@/session/schema"
+import type { Tool as AITool } from "ai"
+import { Effect, Layer, Schema } from "effect"
+
+const ctx: Tool.Context = {
+  sessionID: SessionID.make("ses_code-mode"),
+  messageID: MessageID.make("msg_code-mode"),
+  agent: "build",
+  abort: new AbortController().signal,
+  callID: "call_code_mode",
+  messages: [],
+  metadata: () => Effect.void,
+  ask: () => Effect.void,
+}
+
+// Build a real MCP-derived AI SDK tool over a fake transport, so the adapter exercises
+// the same `convertTool` execution path that `mcp.tools()` produces at runtime.
+function mcpTool(
+  name: string,
+  handler: (args: Record<string, unknown>) => unknown,
+  inputSchema: Record<string, unknown> = { type: "object", properties: {} },
+): AITool {
+  const client = {
+    callTool: async (params: { arguments?: Record<string, unknown> }) => handler(params.arguments ?? {}),
+  }
+  return McpCatalog.convertTool({ name, description: name, inputSchema } as any, client as any)
+}
+
+// Truncate echoes its input so assertions read the exact program output. Agent.get is
+// consulted by the shared wrapper during truncation AND at execute time for the
+// permission ruleset that filters the dispatchable tool tree; Session.get supplies the
+// (empty) session-level ruleset half of that merge. Plugin.trigger defaults to the
+// pass-through the real service uses when no plugin implements a hook; tests observing
+// or failing hooks override it.
+function harness(input: {
+  mcpTools: Record<string, AITool>
+  defs?: Record<string, MCPToolDef>
+  servers: string[]
+  permission?: PermissionV1.Rule[]
+  trigger?: Plugin.Interface["trigger"]
+}) {
+  return Layer.mergeAll(
+    Layer.mock(Plugin.Service, {
+      trigger: input.trigger ?? (((_name, _input, output) => Effect.succeed(output)) as Plugin.Interface["trigger"]),
+    }),
+    Layer.mock(Truncate.Service, {
+      output: (text: string) => Effect.succeed({ content: text, truncated: false as const }),
+    }),
+    Layer.mock(Agent.Service, {
+      get: () => Effect.succeed({ name: "build", permission: input.permission ?? [] } as any),
+    }),
+    Layer.mock(Session.Service, {
+      get: () => Effect.succeed({ permission: [] } as any),
+    }),
+    Layer.mock(MCP.Service, {
+      tools: () => Effect.succeed(input.mcpTools),
+      defs: () => Effect.succeed(input.defs ?? {}),
+      clients: () => Effect.succeed(Object.fromEntries(input.servers.map((name) => [name, {} as any]))),
+    }),
+  )
+}
+
+// Derive sanitized server namespaces from the catalog keys, mirroring how the registry
+// passes `Object.keys(mcp.clients()).map(sanitize)`.
+function serverNames(mcpTools: Record<string, AITool>, servers?: string[]) {
+  return servers ?? [...new Set(Object.keys(mcpTools).map((key) => key.split("_")[0]!))]
+}
+
+function build(
+  mcpTools: Record<string, AITool>,
+  defs: Record<string, MCPToolDef> = {},
+  servers?: string[],
+  permission?: PermissionV1.Rule[],
+  trigger?: Plugin.Interface["trigger"],
+) {
+  const names = serverNames(mcpTools, servers)
+  return Effect.runPromise(
+    CodeModeTool.pipe(
+      Effect.flatMap(Tool.init),
+      Effect.provide(harness({ mcpTools, defs, servers: names, permission, trigger })),
+    ),
+  )
+}
+
+// The agent-facing description, as the registry composes it (`describeCodeMode`):
+// permission-filtered tool set → grouped catalog → CodeMode instructions.
+function describeFor(
+  mcpTools: Record<string, AITool>,
+  defs: Record<string, MCPToolDef> = {},
+  servers?: string[],
+  permission: PermissionV1.Rule[] = [],
+) {
+  return catalogInstructions(Permission.visibleTools(mcpTools, permission), defs, serverNames(mcpTools, servers))
+}
+
+describe("code mode execute", () => {
+  test("defines execute input with an Effect schema", async () => {
+    const decode = Schema.decodeUnknownEffect(Parameters)
+    await expect(Effect.runPromise(decode({ code: "return 1" }))).resolves.toEqual({ code: "return 1" })
+    await expect(Effect.runPromise(decode({}))).rejects.toThrow()
+  })
+
+  test("groups multi-underscore server names by longest matching prefix", () => {
+    const groups = groupByServer({ my_server_do_thing: mcpTool("do_thing", () => "") }, ["my_server"])
+    expect([...groups.keys()]).toEqual(["my_server"])
+    expect(groups.get("my_server")![0]).toMatchObject({
+      path: "my_server.do_thing",
+      local: "do_thing",
+      key: "my_server_do_thing",
+    })
+  })
+
+  test("groupByServer uses the whole key as the server name when it has no underscore", () => {
+    const groups = groupByServer({ standalone: mcpTool("standalone", () => "") }, [])
+    expect([...groups.keys()]).toEqual(["standalone"])
+    expect(groups.get("standalone")![0]).toMatchObject({
+      path: "standalone.standalone",
+      server: "standalone",
+      local: "standalone",
+      key: "standalone",
+    })
+  })
+
+  test("groupByServer carries the raw MCP schemas for rendering", () => {
+    const defs: Record<string, MCPToolDef> = {
+      weather_current: {
+        name: "current",
+        inputSchema: { type: "object", properties: { city: { type: "string" } }, required: ["city"] },
+        outputSchema: { type: "object", properties: { tempC: { type: "number" } }, required: ["tempC"] },
+      } as any,
+    }
+    const groups = groupByServer({ weather_current: mcpTool("current", () => "") }, ["weather"], defs)
+    const entry = groups.get("weather")![0]!
+    expect(entry.inputSchema).toEqual(defs.weather_current!.inputSchema as any)
+    expect(entry.outputSchema).toEqual(defs.weather_current!.outputSchema as any)
+  })
+
+  test("the static base description carries no catalog; the registry appends it", async () => {
+    const tool = await build({ github_list_issues: mcpTool("list_issues", () => "") })
+    expect(tool.id).toBe(CODE_MODE_TOOL)
+    expect(tool.description).toContain("confined runtime")
+    expect(tool.description).not.toContain("Available tools")
+    expect(tool.description).not.toContain("list_issues")
+  })
+
+  test("small catalogs inline every full signature in the appended catalog", () => {
+    const description = describeFor({
+      github_create_issue: mcpTool("create_issue", () => "", {
+        type: "object",
+        properties: { title: { type: "string" }, body: { type: "string" } },
+        required: ["title"],
+      }),
+      github_list_issues: mcpTool("list_issues", () => ""),
+      linear_search: mcpTool("search", () => ""),
+    })
+
+    expect(description).toContain("Available tools (COMPLETE list")
+    expect(description).toContain("- github (2 tools)")
+    expect(description).toContain("- linear (1 tool)")
+    expect(description).toContain(
+      "tools.github.create_issue(input: { title: string; body?: string }): Promise<unknown>",
+    )
+    expect(description).toContain("tools.github.list_issues(")
+    expect(description).toContain("tools.linear.search(")
+    // A schema with no properties renders as an empty object, not `{  }`.
+    expect(description).toContain("tools.linear.search(input: {}): Promise<unknown>")
+    // Fully inlined catalog: no discovery round-trip is needed or advertised.
+    expect(description).not.toContain("$codemode")
+    expect(description).not.toContain("Browse one namespace")
+    // The workflow/rules sections use placeholder call forms only — the example machinery
+    // never cherry-picks a catalog tool or fabricates result fields.
+    expect(description).toContain("## Workflow")
+    expect(description).toContain("1. Pick a tool from the list under `## Available tools`")
+    expect(description).toContain('`const data = typeof res === "string" ? JSON.parse(res) : res` - most tools return JSON as a string')
+    expect(description).toContain("Return only the fields you need")
+    expect(description).not.toContain("total_count")
+  })
+
+  test("signatures render the declared outputSchema as the return type", () => {
+    const defs: Record<string, MCPToolDef> = {
+      weather_current: {
+        name: "current",
+        inputSchema: { type: "object", properties: { city: { type: "string" } }, required: ["city"] },
+        outputSchema: {
+          type: "object",
+          properties: { tempC: { type: "number" }, summary: { type: "string" } },
+          required: ["tempC"],
+        },
+      } as any,
+    }
+    const description = describeFor({ weather_current: mcpTool("current", () => "") }, defs)
+    expect(description).toContain(
+      "tools.weather.current(input: { city: string }): Promise<{ tempC: number; summary?: string }>",
+    )
+  })
+
+  test("large catalogs inline a budgeted PARTIAL list plus runtime search", async () => {
+    const tools: Record<string, AITool> = {}
+    const filler = "a searchable description of this operation that consumes catalog budget ".repeat(3)
+    for (let i = 0; i < 150; i++) {
+      const client = { callTool: async () => ({ content: [] }) }
+      tools[`alpha_op_${i}`] = McpCatalog.convertTool(
+        {
+          name: `op_${i}`,
+          description: `${filler}${i}`,
+          inputSchema: { type: "object", properties: { value: { type: "string" }, count: { type: "number" } } },
+        } as any,
+        client as any,
+      )
+    }
+    tools["zeta_only_tool"] = mcpTool("only_tool", () => "", {
+      type: "object",
+      properties: { topic: { type: "string", description: "Subject to look up" } },
+      required: ["topic"],
+    })
+    const description = describeFor(tools, {}, ["alpha", "zeta"])
+
+    // Every namespace is listed with counts; signatures inline round-robin across
+    // namespaces (cheapest-first within each) until the budget runs out, and the
+    // description states exactly how comprehensive the list is. Round-robin fairness:
+    // the small zeta namespace is fully shown even though alpha alone could exhaust
+    // the whole budget.
+    expect(description).toContain("Available tools (PARTIAL - ")
+    expect(description).toMatch(/- alpha \(150 tools, \d+ shown\)/)
+    expect(description).toContain("- zeta (1 tool)\n")
+    expect(description).toContain("tools.zeta.only_tool(input: { topic: string }): Promise<unknown>")
+    expect(description).toContain("tools.$codemode.search(")
+    // PARTIAL catalogs put search first in the workflow and advertise namespace browsing.
+    expect(description).toContain("1. Find a tool (skip when it is already listed below)")
+    expect(description).toContain('- Browse one namespace: `await tools.$codemode.search({ query: "", namespace: "<name>" })`.')
+    expect(description).not.toContain("total_count")
+    // All op lines cost the same estimated tokens (chars/4 rounds away the 1- vs 3-digit
+    // name difference), so the path tiebreak decides: the lexicographically-first ops made
+    // the cut and the lexicographic tail (op_99 is maximal) did not.
+    expect(description).toContain("tools.alpha.op_0(")
+    expect(description).not.toContain("tools.alpha.op_99(")
+
+    // The runtime search tool works in-program and returns complete signatures.
+    const tool = await build(tools, {}, ["alpha", "zeta"])
+    const out = await Effect.runPromise(
+      tool.execute({ code: "return await tools.$codemode.search({ query: 'only tool', limit: 3 })" }, ctx),
+    )
+    const result = JSON.parse(out.output)
+    // Search-result paths carry the `tools.` prefix so each is directly usable as a call site.
+    expect(result.items.map((i: any) => i.path)).toContain("tools.zeta.only_tool")
+    expect(result.items[0].signature).toContain("tools.")
+    // Search results render the pretty multiline signature: MCP input-property
+    // descriptions ride along as JSDoc field comments. The inline catalog stays compact.
+    const signature = result.items.find((i: any) => i.path === "tools.zeta.only_tool").signature
+    expect(signature).toContain("tools.zeta.only_tool(input: {\n")
+    expect(signature).toContain("  /** Subject to look up */\n  topic: string")
+    expect(description).not.toContain("/**")
+    expect(out.metadata.toolCalls).toEqual([
+      { tool: "$codemode.search", status: "completed", input: { query: "only tool", limit: 3 } },
+    ])
+  })
+
+  test("runs plain JavaScript and returns the value as text", async () => {
+    const tool = await build({})
+    const output = await Effect.runPromise(tool.execute({ code: "return 1 + 2" }, ctx))
+    expect(output.output).toBe("3")
+    expect(output.metadata.toolCalls).toEqual([])
+  })
+
+  test("Object.keys(tools) enumerates the MCP server namespaces", async () => {
+    const tool = await build({
+      github_list_issues: mcpTool("list_issues", () => ""),
+      linear_search: mcpTool("search", () => ""),
+    })
+    const output = await Effect.runPromise(
+      tool.execute({ code: "const namespaces = Object.keys(tools); return { namespaces, count: namespaces.length }" }, ctx),
+    )
+    expect(JSON.parse(output.output)).toEqual({ namespaces: ["github", "linear"], count: 2 })
+  })
+
+  test("calls a namespaced MCP tool and flows its text result back into the program", async () => {
+    const seen: Record<string, unknown>[] = []
+    const tool = await build({
+      greeter_hello: mcpTool("hello", (args) => {
+        seen.push(args)
+        return { content: [{ type: "text", text: `hello ${args.name}` }] }
+      }),
+    })
+
+    const output = await Effect.runPromise(
+      tool.execute({ code: "const r = await tools.greeter.hello({ name: 'world' }); return r.toUpperCase()" }, ctx),
+    )
+
+    expect(seen).toEqual([{ name: "world" }])
+    expect(output.output).toBe("HELLO WORLD")
+    expect(output.metadata.toolCalls).toEqual([
+      { tool: "greeter.hello", status: "completed", input: { name: "world" } },
+    ])
+  })
+
+  test("exposes structured content as native data and composes multiple calls", async () => {
+    const tool = await build({
+      math_add: mcpTool("add", (args) => ({
+        content: [],
+        structuredContent: { sum: (args.a as number) + (args.b as number) },
+      })),
+    })
+
+    const output = await Effect.runPromise(
+      tool.execute(
+        {
+          code: `
+            const first = await tools.math.add({ a: 1, b: 2 })
+            const second = await tools.math.add({ a: first.sum, b: 10 })
+            return { total: second.sum }
+          `,
+        },
+        ctx,
+      ),
+    )
+
+    expect(JSON.parse(output.output)).toEqual({ total: 13 })
+    expect(output.metadata.toolCalls).toEqual([
+      { tool: "math.add", status: "completed", input: { a: 1, b: 2 } },
+      { tool: "math.add", status: "completed", input: { a: 3, b: 10 } },
+    ])
+  })
+
+  test("runs tool calls in parallel with Promise.all", async () => {
+    const tool = await build({
+      echo_one: mcpTool("one", () => ({ content: [{ type: "text", text: "1" }] })),
+      echo_two: mcpTool("two", () => ({ content: [{ type: "text", text: "2" }] })),
+    })
+
+    const output = await Effect.runPromise(
+      tool.execute(
+        { code: "const [a, b] = await Promise.all([tools.echo.one({}), tools.echo.two({})]); return a + b" },
+        ctx,
+      ),
+    )
+
+    expect(output.output).toBe("12")
+    expect(output.metadata.toolCalls.map((c) => c.tool).sort()).toEqual(["echo.one", "echo.two"])
+    expect(output.metadata.toolCalls.every((c) => c.status === "completed")).toBe(true)
+  })
+
+  test("returns a readable error when the program throws", async () => {
+    const tool = await build({})
+    const output = await Effect.runPromise(tool.execute({ code: "throw new Error('boom')" }, ctx))
+    expect(output.output).toBe("Uncaught: boom")
+    expect(output.metadata.error).toBe(true)
+  })
+
+  test("reports an unknown tool as a failed execution", async () => {
+    const tool = await build({ known_tool: mcpTool("tool", () => "ok") })
+    const output = await Effect.runPromise(tool.execute({ code: "return await tools.known.missing({})" }, ctx))
+    expect(output.metadata.error).toBe(true)
+    expect(output.output).toContain("Unknown tool 'known.missing'")
+  })
+
+  test("propagates an MCP tool error into the program as a catchable failure", async () => {
+    const tool = await build({
+      bad_tool: mcpTool("tool", () => ({ isError: true, content: [{ type: "text", text: "server exploded" }] })),
+    })
+    const output = await Effect.runPromise(
+      tool.execute({ code: "try { await tools.bad.tool({}) } catch (e) { return 'caught: ' + e.message }" }, ctx),
+    )
+    expect(output.output).toBe("caught: server exploded")
+  })
+
+  test("asks permission before each child tool call", async () => {
+    const asked: unknown[] = []
+    const permissionCtx: Tool.Context = { ...ctx, ask: (req) => Effect.sync(() => void asked.push(req)) }
+    const ok = () => ({ content: [{ type: "text", text: "ok" }] })
+    const tool = await build({ a_tool: mcpTool("a", ok), b_tool: mcpTool("b", ok) })
+
+    await Effect.runPromise(
+      tool.execute({ code: "await tools.a.tool({}); await tools.b.tool({}); return 'done'" }, permissionCtx),
+    )
+
+    expect(asked.map((req: any) => req.permission)).toEqual(["a_tool", "b_tool"])
+  })
+
+  test("a denied permission fails the child call with a catchable message, not the whole execute", async () => {
+    const denyCtx: Tool.Context = { ...ctx, ask: () => Effect.die(new Error("permission denied by user")) }
+    const called: string[] = []
+    const tool = await build({
+      a_tool: mcpTool("a", () => {
+        called.push("a")
+        return { content: [{ type: "text", text: "ok" }] }
+      }),
+    })
+
+    const output = await Effect.runPromise(
+      tool.execute({ code: "try { await tools.a.tool({}) } catch (e) { return 'denied: ' + e.message }" }, denyCtx),
+    )
+
+    expect(output.output).toBe("denied: permission denied by user")
+    expect(output.metadata.error).toBeUndefined()
+    // The MCP tool itself never ran.
+    expect(called).toEqual([])
+    expect(output.metadata.toolCalls).toEqual([{ tool: "a.tool", status: "error" }])
+  })
+
+  test("child calls fire plugin tool.execute hooks with the MCP key and synthetic parent/N call ids", async () => {
+    const events: { name: string; input: any; output: any }[] = []
+    const trigger = ((name: unknown, input: unknown, output: unknown) =>
+      Effect.sync(() => {
+        events.push({ name: name as string, input, output })
+        return output
+      })) as Plugin.Interface["trigger"]
+    const tool = await build(
+      {
+        a_tool: mcpTool("a", () => ({ content: [{ type: "text", text: "one" }] })),
+        b_tool: mcpTool("b", () => ({ content: [{ type: "text", text: "two" }] })),
+      },
+      {},
+      undefined,
+      undefined,
+      trigger,
+    )
+
+    const out = await Effect.runPromise(
+      tool.execute({ code: "await tools.a.tool({ x: 1 }); await tools.b.tool({}); return 'done'" }, ctx),
+    )
+
+    expect(out.output).toBe("done")
+    // callID is synthetic and per-execution: `${parentCallID}/${n}`, n starting at 1.
+    expect(events.map((e) => [e.name, e.input.tool, e.input.callID])).toEqual([
+      ["tool.execute.before", "a_tool", "call_code_mode/1"],
+      ["tool.execute.after", "a_tool", "call_code_mode/1"],
+      ["tool.execute.before", "b_tool", "call_code_mode/2"],
+      ["tool.execute.after", "b_tool", "call_code_mode/2"],
+    ])
+    const [before, after] = events
+    expect(before!.input.sessionID).toBe(ctx.sessionID)
+    expect(before!.output).toEqual({ args: { x: 1 } })
+    expect(after!.input.args).toEqual({ x: 1 })
+    // The after hook sees the raw MCP result — the same payload the legacy path passes.
+    expect(after!.output).toEqual({ content: [{ type: "text", text: "one" }] })
+  })
+
+  test("a failing before hook fails only that child call as a catchable in-program error", async () => {
+    const trigger = ((name: unknown, input: any, output: unknown) => {
+      if (name === "tool.execute.before" && input.tool === "a_tool") return Effect.die(new Error("hook exploded"))
+      return Effect.succeed(output)
+    }) as Plugin.Interface["trigger"]
+    const called: string[] = []
+    const record = (name: string) => () => {
+      called.push(name)
+      return { content: [{ type: "text", text: "ok" }] }
+    }
+    const tool = await build(
+      { a_tool: mcpTool("a", record("a")), b_tool: mcpTool("b", record("b")) },
+      {},
+      undefined,
+      undefined,
+      trigger,
+    )
+
+    const out = await Effect.runPromise(
+      tool.execute(
+        {
+          code: `
+            let caught
+            try { await tools.a.tool({}) } catch (e) { caught = e.message }
+            const r = await tools.b.tool({})
+            return caught + " / " + r
+          `,
+        },
+        ctx,
+      ),
+    )
+
+    // The program handled the hook failure; the rest ran and the outer result is ok.
+    expect(out.metadata.error).toBeUndefined()
+    expect(out.output).toBe("hook exploded / ok")
+    // The before hook gates dispatch: the failed child's tool never executed.
+    expect(called).toEqual(["b"])
+  })
+
+  test("streams live per-call metadata as a call starts and finishes", async () => {
+    const snapshots: Array<{ toolCalls: { tool: string; status: string; input?: Record<string, unknown> }[] }> = []
+    const recordingCtx: Tool.Context = {
+      ...ctx,
+      metadata: (val: any) => Effect.sync(() => void snapshots.push(val.metadata)),
+    }
+    const tool = await build({ greeter_hello: mcpTool("hello", () => ({ content: [{ type: "text", text: "hi" }] })) })
+
+    await Effect.runPromise(
+      tool.execute({ code: "await tools.greeter.hello({ name: 'Ada' }); return 'done'" }, recordingCtx),
+    )
+
+    // The UI sees the call appear as running, then resolve to completed.
+    expect(snapshots).toContainEqual({
+      toolCalls: [{ tool: "greeter.hello", status: "running", input: { name: "Ada" } }],
+    })
+    expect(snapshots).toContainEqual({
+      toolCalls: [{ tool: "greeter.hello", status: "completed", input: { name: "Ada" } }],
+    })
+  })
+
+  test("marks a failed child call as error in the live metadata", async () => {
+    const snapshots: Array<{ toolCalls: { tool: string; status: string; input?: Record<string, unknown> }[] }> = []
+    const recordingCtx: Tool.Context = {
+      ...ctx,
+      metadata: (val: any) => Effect.sync(() => void snapshots.push(val.metadata)),
+    }
+    const tool = await build({
+      bad_tool: mcpTool("tool", () => ({ isError: true, content: [{ type: "text", text: "boom" }] })),
+    })
+
+    await Effect.runPromise(
+      tool.execute(
+        { code: "try { await tools.bad.tool({ reason: 'test' }) } catch (e) { return 'caught' }" },
+        recordingCtx,
+      ),
+    )
+
+    expect(snapshots).toContainEqual({ toolCalls: [{ tool: "bad.tool", status: "error", input: { reason: "test" } }] })
+  })
+
+  test("accumulates stripped media as execute attachments the sandbox never sees", async () => {
+    const tool = await build({
+      shot_take: mcpTool("take", () => ({
+        content: [{ type: "image", data: "PNGDATA", mimeType: "image/png" }],
+        structuredContent: { name: "shot.png" },
+      })),
+    })
+
+    const out = await Effect.runPromise(tool.execute({ code: "return await tools.shot.take({})" }, ctx))
+    // The program received the structured content; the media rode along host-side.
+    expect(JSON.parse(out.output)).toEqual({ name: "shot.png" })
+    expect(out.attachments).toEqual([{ type: "file", mime: "image/png", url: "data:image/png;base64,PNGDATA" }])
+    expect(out.output).not.toContain("PNGDATA")
+  })
+
+  test("a media-only result returns a text marker so the program knows it succeeded", async () => {
+    const tool = await build({
+      shot_take: mcpTool("take", () => ({ content: [{ type: "image", data: "PNGDATA", mimeType: "image/png" }] })),
+    })
+    const out = await Effect.runPromise(tool.execute({ code: "return await tools.shot.take({})" }, ctx))
+    expect(out.output).toBe("[1 image attached to the result]")
+    expect(out.attachments).toEqual([{ type: "file", mime: "image/png", url: "data:image/png;base64,PNGDATA" }])
+  })
+
+  test("attachments still flow when the program returns something else entirely", async () => {
+    const tool = await build({
+      shot_take: mcpTool("take", () => ({ content: [{ type: "image", data: "PNGDATA", mimeType: "image/png" }] })),
+    })
+    const out = await Effect.runPromise(
+      tool.execute({ code: "await tools.shot.take({}); return 'captured'" }, ctx),
+    )
+    expect(out.output).toBe("captured")
+    expect(out.attachments).toHaveLength(1)
+  })
+
+  test("isolates the sandbox from host globals", async () => {
+    const tool = await build({})
+    const output = await Effect.runPromise(tool.execute({ code: "return process.env" }, ctx))
+    expect(output.metadata.error).toBe(true)
+  })
+
+  test("cancelling via ctx.abort interrupts the running program", async () => {
+    // The child call triggers the abort itself, deterministically, while the program
+    // swallows the call's failure and heads into an infinite loop. If abort did not
+    // interrupt the execution fiber, this test would hang on the busy loop.
+    const controller = new AbortController()
+    const tool = await build({
+      host_trigger: mcpTool("trigger", () => {
+        controller.abort()
+        return new Promise(() => {})
+      }),
+    })
+    const output = await Effect.runPromise(
+      tool.execute(
+        { code: "try { await tools.host.trigger({}) } catch {} while (true) {}" },
+        { ...ctx, abort: controller.signal },
+      ),
+    )
+    expect(output.output).toBe("Execution cancelled.")
+    expect(output.metadata.error).toBe(true)
+    expect(output.metadata.toolCalls).toEqual([{ tool: "host.trigger", status: "running" }])
+  })
+
+  test("a pre-aborted signal cancels before the program runs", async () => {
+    const controller = new AbortController()
+    controller.abort()
+    const ran: string[] = []
+    const tool = await build({ host_touch: mcpTool("touch", () => (ran.push("called"), "ok")) })
+    const output = await Effect.runPromise(
+      tool.execute({ code: "return await tools.host.touch({})" }, { ...ctx, abort: controller.signal }),
+    )
+    expect(output.output).toBe("Execution cancelled.")
+    expect(ran).toEqual([])
+  })
+
+  test("leaves oversized results to OpenCode's native tool-output truncation", async () => {
+    // No CodeMode output limit is set, so the full result reaches the shared Tool.define
+    // wrapper intact (the harness Truncate fake passes it through un-truncated).
+    const tool = await build({})
+    const output = await Effect.runPromise(tool.execute({ code: "return 'x'.repeat(40000)" }, ctx))
+    expect(output.metadata.error).toBeUndefined()
+    expect(output.output).not.toContain("[result truncated:")
+    expect(output.output.length).toBeGreaterThanOrEqual(40_000)
+  })
+
+  test("appends logs after the result on success and after the message on error", async () => {
+    const tool = await build({})
+
+    const ok = await Effect.runPromise(
+      tool.execute({ code: "console.log('step one'); console.warn('careful'); return 'done'" }, ctx),
+    )
+    expect(ok.output).toBe("done\n\nLogs:\nstep one\n[warn] careful")
+
+    const err = await Effect.runPromise(
+      tool.execute({ code: "console.log('before the throw'); throw new Error('boom')" }, ctx),
+    )
+    expect(err.metadata.error).toBe(true)
+    expect(err.output).toContain("Uncaught: boom")
+    expect(err.output).toContain("Logs:\nbefore the throw")
+  })
+})
+
+describe("code mode permission visibility", () => {
+  const deny = (permission: string): PermissionV1.Rule => ({ permission, pattern: "*", action: "deny" })
+  const askRule = (permission: string): PermissionV1.Rule => ({ permission, pattern: "*", action: "ask" })
+  const ok = () => ({ content: [{ type: "text", text: "ok" }] })
+
+  test("a hard-denied tool never enters the catalog or its search index", () => {
+    const mcpTools = {
+      github_create_issue: mcpTool("create_issue", ok),
+      github_list_issues: mcpTool("list_issues", ok),
+    }
+    const description = describeFor(mcpTools, {}, ["github"], [deny("github_create_issue")])
+    expect(description).toContain("tools.github.list_issues(")
+    expect(description).not.toContain("create_issue")
+    expect(description).toContain("- github (1 tool)")
+  })
+
+  test("an ask-level tool stays fully visible in the catalog", () => {
+    const mcpTools = {
+      github_create_issue: mcpTool("create_issue", ok),
+      github_list_issues: mcpTool("list_issues", ok),
+    }
+    const description = describeFor(mcpTools, {}, ["github"], [askRule("github_create_issue")])
+    expect(description).toContain("tools.github.create_issue(")
+    expect(description).toContain("tools.github.list_issues(")
+    expect(description).toContain("- github (2 tools)")
+  })
+
+  test("a hard-denied tool is not dispatchable: the program gets the unknown-tool diagnostic", async () => {
+    const called: string[] = []
+    const tool = await build(
+      {
+        github_create_issue: mcpTool("create_issue", () => {
+          called.push("create_issue")
+          return ok()
+        }),
+        github_list_issues: mcpTool("list_issues", ok),
+      },
+      {},
+      ["github"],
+      [deny("github_create_issue")],
+    )
+
+    const denied = await Effect.runPromise(
+      tool.execute({ code: "return await tools.github.create_issue({ title: 'x' })" }, ctx),
+    )
+    expect(denied.metadata.error).toBe(true)
+    expect(denied.output).toContain("Unknown tool 'github.create_issue'")
+    expect(denied.output).not.toContain("permission")
+    expect(called).toEqual([])
+
+    // The rest of the namespace still works.
+    const allowed = await Effect.runPromise(
+      tool.execute({ code: "return await tools.github.list_issues({})" }, ctx),
+    )
+    expect(allowed.metadata.error).toBeUndefined()
+    expect(allowed.output).toBe("ok")
+  })
+
+  test("an ask-level tool remains callable and still prompts via ctx.ask", async () => {
+    const asked: string[] = []
+    const askCtx: Tool.Context = { ...ctx, ask: (req) => Effect.sync(() => void asked.push(req.permission)) }
+    const tool = await build(
+      { github_list_issues: mcpTool("list_issues", ok) },
+      {},
+      ["github"],
+      [askRule("github_list_issues")],
+    )
+    const out = await Effect.runPromise(
+      tool.execute({ code: "return await tools.github.list_issues({})" }, askCtx),
+    )
+    expect(out.output).toBe("ok")
+    expect(asked).toEqual(["github_list_issues"])
+  })
+
+  test("Permission.visibleTools hides only hard denies, matching Permission.disabled", () => {
+    const tools = { a_tool: 1, b_tool: 2, c_tool: 3 }
+    const visible = Permission.visibleTools(tools, [
+      deny("a_tool"),
+      askRule("b_tool"),
+      // A scoped (non-"*") deny does not hide the tool from the catalog.
+      { permission: "c_tool", pattern: "something", action: "deny" },
+    ])
+    expect(Object.keys(visible)).toEqual(["b_tool", "c_tool"])
+  })
+})
+
+describe("toSandboxResult", () => {
+  const collector = () => {
+    const attachments: Attachment[] = []
+    return { attachments, collect: (a: Attachment) => void attachments.push(a) }
+  }
+
+  test("prefers structuredContent over text", () => {
+    const { collect } = collector()
+    expect(toSandboxResult({ structuredContent: { x: 1 }, content: [{ type: "text", text: "hi" }] }, collect)).toEqual(
+      { x: 1 },
+    )
+  })
+
+  test("joins text content when no structured content is present", () => {
+    const { collect } = collector()
+    expect(
+      toSandboxResult(
+        { content: [{ type: "text", text: "one" }, { type: "text", text: "two" }] },
+        collect,
+      ),
+    ).toBe("one\ntwo")
+  })
+
+  test("passes non-MCP values through untouched", () => {
+    const { collect } = collector()
+    expect(toSandboxResult("raw", collect)).toBe("raw")
+    expect(toSandboxResult(42, collect)).toBe(42)
+    expect(toSandboxResult(null, collect)).toBeNull()
+    expect(toSandboxResult({ some: "object" }, collect)).toEqual({ some: "object" })
+  })
+
+  test("strips media into the accumulator; text stays the sandbox value", () => {
+    const { attachments, collect } = collector()
+    const value = toSandboxResult(
+      {
+        content: [
+          { type: "text", text: "see image" },
+          { type: "image", data: "AAAA", mimeType: "image/png" },
+        ],
+      },
+      collect,
+    )
+    expect(value).toBe("see image")
+    expect(attachments).toEqual([{ type: "file", mime: "image/png", url: "data:image/png;base64,AAAA" }])
+  })
+
+  test("a media-only result yields a marker; counts and nouns follow the content", () => {
+    const one = collector()
+    expect(toSandboxResult({ content: [{ type: "image", data: "A", mimeType: "image/png" }] }, one.collect)).toBe(
+      "[1 image attached to the result]",
+    )
+
+    const two = collector()
+    expect(
+      toSandboxResult(
+        {
+          content: [
+            { type: "image", data: "A", mimeType: "image/png" },
+            { type: "image", data: "B", mimeType: "image/jpeg" },
+          ],
+        },
+        two.collect,
+      ),
+    ).toBe("[2 images attached to the result]")
+    expect(two.attachments).toHaveLength(2)
+
+    const mixed = collector()
+    expect(
+      toSandboxResult(
+        {
+          content: [
+            { type: "image", data: "A", mimeType: "image/png" },
+            { type: "audio", data: "B", mimeType: "audio/wav" },
+          ],
+        },
+        mixed.collect,
+      ),
+    ).toBe("[2 files attached to the result]")
+  })
+
+  test("extracts embedded resources: text inline, blobs as attachments with filenames", () => {
+    const { attachments, collect } = collector()
+    const value = toSandboxResult(
+      {
+        content: [
+          { type: "resource", resource: { uri: "file:///tmp/notes.txt", mimeType: "text/plain", text: "note text" } },
+          { type: "resource", resource: { uri: "file:///tmp/doc.pdf", mimeType: "application/pdf", blob: "PDF" } },
+        ],
+      },
+      collect,
+    )
+    expect(value).toBe("note text")
+    expect(attachments).toEqual([
+      { type: "file", mime: "application/pdf", url: "data:application/pdf;base64,PDF", filename: "doc.pdf" },
+    ])
+  })
+
+  test("collects resource_link blocks as external-URL attachments", () => {
+    const { attachments, collect } = collector()
+    const value = toSandboxResult(
+      { content: [{ type: "resource_link", uri: "https://example.com/report.csv", mimeType: "text/csv" }] },
+      collect,
+    )
+    expect(value).toBe("[1 file attached to the result]")
+    expect(attachments).toEqual([
+      { type: "file", mime: "text/csv", url: "https://example.com/report.csv", filename: "report.csv" },
+    ])
+  })
+
+  test("an MCP-shaped result with nothing extractable becomes null", () => {
+    const { collect } = collector()
+    expect(toSandboxResult({ content: [] }, collect)).toBeNull()
+    expect(toSandboxResult({ content: [{ type: "mystery" }] }, collect)).toBeNull()
+  })
+})
+
+describe("formatting helpers", () => {
+  test("formatValue", () => {
+    expect(formatValue("text")).toBe("text")
+    expect(formatValue({ a: 1 })).toBe(JSON.stringify({ a: 1 }, null, 2))
+    expect(formatValue(null)).toBe("null")
+    expect(formatValue(undefined)).toBe("undefined")
+  })
+
+  test("withLogs", () => {
+    // No logs: output is returned untouched.
+    expect(withLogs("result", [])).toBe("result")
+    expect(withLogs("result")).toBe("result")
+    // Logs are appended as a trailing section, one line each.
+    expect(withLogs("result", ["a", "[warn] b"])).toBe("result\n\nLogs:\na\n[warn] b")
+    // Empty output still gets the section (no leading blank lines).
+    expect(withLogs("", ["[error] boom"])).toBe("Logs:\n[error] boom")
+  })
+})

packages/opencode/test/tool/registry.test.ts

@@ -17,6 +17,8 @@ import { InstanceState } from "@/effect/instance-state"
 import { ToolJsonSchema } from "@/tool/json-schema"
 import { MessageID, SessionID } from "@/session/schema"
 import { RuntimeFlags } from "@/effect/runtime-flags"
+import { MCP } from "@/mcp"
+import { McpCatalog } from "@/mcp/catalog"
 import { ProviderV2 } from "@opencode-ai/core/provider"
 import { ModelV2 } from "@opencode-ai/core/model"
 
@@ -57,6 +59,45 @@ const replacements = [
 const it = testEffect(LayerNode.compile(root, replacements))
 const withBrokenPlugin = testEffect(LayerNode.compile(root, [...replacements, [Plugin.node, brokenPluginLayer]]))
 
+// Fake MCP.Service serving two tools on one server, built through the same
+// `convertTool` path the real service uses so the code-mode catalog renders
+// genuine signatures.
+function fakeMcpLayer(tools: Record<string, { description: string }>) {
+  const client = { callTool: async () => ({ content: [] }) }
+  const converted = Object.fromEntries(
+    Object.entries(tools).map(([key, def]) => [
+      key,
+      McpCatalog.convertTool(
+        {
+          name: key,
+          description: def.description,
+          inputSchema: { type: "object", properties: {} },
+        } as any,
+        client as any,
+      ),
+    ]),
+  )
+  return Layer.mock(MCP.Service, {
+    tools: () => Effect.succeed(converted),
+    defs: () => Effect.succeed({}),
+    clients: () => Effect.succeed(Object.keys(tools).length > 0 ? ({ github: {} } as any) : {}),
+  })
+}
+
+const mcpToolsLayer = fakeMcpLayer({
+  github_create_issue: { description: "Create an issue" },
+  github_list_issues: { description: "List issues" },
+})
+
+const codeModeFlags = [RuntimeFlags.node, RuntimeFlags.layer({ experimentalCodeMode: true })] as const
+const withCodeMode = testEffect(
+  LayerNode.compile(root, [[Config.node, configLayer], codeModeFlags, [MCP.node, mcpToolsLayer]]),
+)
+const withCodeModeNoMcp = testEffect(
+  LayerNode.compile(root, [[Config.node, configLayer], codeModeFlags, [MCP.node, fakeMcpLayer({})]]),
+)
+const withFlagOff = testEffect(LayerNode.compile(root, [...replacements, [MCP.node, mcpToolsLayer]]))
+
 afterEach(async () => {
   await disposeAllInstances()
 })
@@ -491,3 +532,82 @@ describe("tool.registry", () => {
     }),
   )
 })
+
+describe("tool.registry code mode", () => {
+  const model = { providerID: ProviderV2.ID.opencode, modelID: ModelV2.ID.make("test") }
+
+  withCodeMode.instance("registers the code-mode execute tool when the flag is on and MCP tools exist", () =>
+    Effect.gen(function* () {
+      const registry = yield* ToolRegistry.Service
+      const agents = yield* Agent.Service
+      const tools = yield* registry.tools({ ...model, agent: yield* agents.defaultInfo() })
+      const execute = tools.find((tool) => tool.id === "execute")
+      if (!execute) throw new Error("code-mode execute tool was not registered")
+      // The registry appends the grouped catalog to the static base description.
+      expect(execute.description).toContain("confined runtime")
+      expect(execute.description).toContain("## Available tools")
+      expect(execute.description).toContain("tools.github.create_issue(")
+      expect(execute.description).toContain("tools.github.list_issues(")
+    }),
+  )
+
+  withCodeModeNoMcp.instance("does not register code mode when no MCP tools are connected", () =>
+    Effect.gen(function* () {
+      const registry = yield* ToolRegistry.Service
+      const agents = yield* Agent.Service
+      const tools = yield* registry.tools({ ...model, agent: yield* agents.defaultInfo() })
+      expect(tools.map((tool) => tool.id)).not.toContain("execute")
+    }),
+  )
+
+  withFlagOff.instance("does not register code mode when the flag is off, even with MCP tools", () =>
+    Effect.gen(function* () {
+      const registry = yield* ToolRegistry.Service
+      const agents = yield* Agent.Service
+      const tools = yield* registry.tools({ ...model, agent: yield* agents.defaultInfo() })
+      expect(tools.map((tool) => tool.id)).not.toContain("execute")
+    }),
+  )
+
+  withCodeMode.instance("hard-denied MCP tools are dropped from the catalog; ask-level ones stay", () =>
+    Effect.gen(function* () {
+      const registry = yield* ToolRegistry.Service
+      const agents = yield* Agent.Service
+      const base = yield* agents.defaultInfo()
+      const agent = {
+        ...base,
+        permission: [
+          ...base.permission,
+          { permission: "github_create_issue", pattern: "*" as const, action: "deny" as const },
+          { permission: "github_list_issues", pattern: "*" as const, action: "ask" as const },
+        ],
+      }
+      const tools = yield* registry.tools({ ...model, agent })
+      const execute = tools.find((tool) => tool.id === "execute")
+      if (!execute) throw new Error("code-mode execute tool was not registered")
+      expect(execute.description).not.toContain("create_issue")
+      expect(execute.description).toContain("tools.github.list_issues(")
+      expect(execute.description).toContain("- github (1 tool)")
+    }),
+  )
+
+  withCodeMode.instance("session-level hard-denied MCP tools are dropped from the code-mode catalog", () =>
+    Effect.gen(function* () {
+      const registry = yield* ToolRegistry.Service
+      const agents = yield* Agent.Service
+      const tools = yield* registry.tools({
+        ...model,
+        agent: yield* agents.defaultInfo(),
+        permission: [
+          { permission: "github_create_issue", pattern: "*" as const, action: "deny" as const },
+          { permission: "github_list_issues", pattern: "*" as const, action: "ask" as const },
+        ],
+      })
+      const execute = tools.find((tool) => tool.id === "execute")
+      if (!execute) throw new Error("code-mode execute tool was not registered")
+      expect(execute.description).not.toContain("create_issue")
+      expect(execute.description).toContain("tools.github.list_issues(")
+      expect(execute.description).toContain("- github (1 tool)")
+    }),
+  )
+})