fix(code-mode): generalize failures and bound diagnostics

packages/code-runtime/code-runtime/README.md

@@ -16,7 +16,7 @@ Semantics every implementation must honor (contract details in the class JSDoc):
 
 ## Vocabulary
 
-`CodeRunRequest` (`program`, `bindings`, `signal?`) carries everything the runtime acts on — defaulting (time budgets and outer-output cap) is the implementation's validated config, never a hidden `??` inside `run()`. `bindings` is a list of `CodeBindingNamespace`s (`global` + `functions`), each exposed to the program as one global object of async callables returning `CodeJsonValue`, the seam-local structural equivalent of canonical `JsonValue` that keeps this interface package independent of sessions. `CodeRunResult` reports the lossless JSON completion `value?`, ordered `logs: string[]`, and the `error?` (`CodeRunFailure`: `kind` + model-feedable `message`). See `src/types.ts` for the full contracts.
+`CodeRunRequest` (`program`, `bindings`, `signal?`) carries everything the runtime acts on — defaulting (time budgets and outer-output cap) is the implementation's validated config, never a hidden `??` inside `run()`. `bindings` is a list of `CodeBindingNamespace`s (`global` + `functions` + optional `errorClass`), each exposed to the program as one global object of async callables returning `CodeJsonValue`, the seam-local structural equivalent of canonical `JsonValue` that keeps this interface package independent of sessions. An `errorClass` descriptor names a real program-global constructor and the own property that receives the rejected member name; runtimes remain independent of consumer terms such as `ToolCallError`. `CodeRunResult` reports the lossless JSON completion `value?`, ordered `logs: string[]`, and the `error?` (`CodeRunFailure`: `kind` + model-feedable `message`). See `src/types.ts` for the full contracts.
 
 ## Model Experience
 

packages/code-runtime/code-runtime/src/index.ts

@@ -8,6 +8,7 @@ import { Context, Service } from 'cordis'
 import type { CodeRunRequest, CodeRunResult } from './types.ts'
 
 export type {
+  CodeBindingErrorClass,
   CodeBindingFunction,
   CodeBindingNamespace,
   CodeJsonValue,
@@ -25,8 +26,9 @@ declare module 'cordis' {
 /**
  * Registers one `ctx.codeRuntime` implementation. Program, budget, abort, and substrate
  * failures resolve in {@link CodeRunResult}; only seam misuse rejects. Implementations bridge
- * structured-cloneable bindings while treating programs as hostile peers, isolate runs from
- * one another, and terminate and await in-flight runs during disposal.
+ * structured-cloneable bindings, materialize each declared namespace rejection
+ * class, treat programs as hostile peers, isolate runs from one another, and
+ * terminate and await in-flight runs during disposal.
  */
 export abstract class CodeRuntime extends Service {
   /**

packages/code-runtime/code-runtime/src/types.ts

@@ -20,6 +20,20 @@ export type CodeBindingFunction = (args: unknown) => Promise<CodeJsonValue>
 /** A lossless JSON value transferable across the dependency-light code-runtime seam. */
 export type CodeJsonValue = null | boolean | number | string | CodeJsonValue[] | { [key: string]: CodeJsonValue }
 
+/**
+ * Program-visible typed rejection for one binding namespace. The runtime
+ * injects a real error constructor under `name`; rejected member calls become
+ * its instances and expose the exact member name through
+ * `memberNameProperty`. Both strings are runtime data rather than knowledge
+ * of a particular consumer such as Code Mode.
+ */
+export interface CodeBindingErrorClass {
+  /** Constructor global and resulting `Error.name` (must be a usable JS identifier). */
+  name: string
+  /** Non-empty own property for the member name; cannot replace `name`, `message`, or `stack`. */
+  memberNameProperty: string
+}
+
 /**
  * A named group of {@link CodeBindingFunction}s the runtime exposes to the
  * program as one global object (e.g. `tools`). Function names are arbitrary
@@ -32,6 +46,8 @@ export interface CodeBindingNamespace {
   global: string
   /** The callable members, keyed by the exact name the program calls. */
   functions: Record<string, CodeBindingFunction>
+  /** Optional program-visible typed rejection contract for this namespace. */
+  errorClass?: CodeBindingErrorClass
 }
 
 /**