feat: return typed values from Code Mode

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

@@ -8,15 +8,15 @@ This package is the interface third of the capability (the bash trio is the temp
 
 | Member | Semantics |
 |---|---|
-| `run(request)` | Execute one program against the request's bindings. **Resolves with an error FIELD for every program outcome** — parse/transform failure, thrown exception, budget expiry, abort, substrate death (`CodeRunFailure`'s orthogonal `kind` taxonomy); it rejects only for caller misuse of the seam itself (e.g. a run submitted after disposal). The program runs as the body of an async function: top-level `await`/`return` work, and the completion value becomes `result.value` when it survives the serialization boundary. |
+| `run(request)` | Execute one program against the request's bindings. **Resolves with an error FIELD for every program outcome** — parse/transform failure, thrown exception, invalid completion, output overflow, budget expiry, abort, or substrate death (`CodeRunFailure`'s orthogonal `kind` taxonomy); it rejects only for caller misuse of the seam itself (e.g. a run submitted after disposal). The program runs as the body of an async function: top-level `await`/`return` work, and a lossless JSON completion becomes `result.value`. |
 | `language` | Readonly descriptor: the source language `run` expects (`'typescript'` is the well-known value). Informational, not gating — a consumer that generates language-specific presentation switches on it and fails loud on a language it cannot present. |
 | `isolation` | Readonly descriptor: the execution substrate (`'worker-thread'`, `'process'`, `'container'`). A label for deployments and diagnostics, **not a security claim**. |
 
-Semantics every implementation must honor (contract details in the class JSDoc): binding calls bridge to the caller's functions verbatim with structured-cloneable arguments/resolutions; the program is treated as a hostile peer (arbitrary binding names are own properties, malformed traffic never crashes the host); no state survives between runs; disposal terminates in-flight runs AND awaits their exit before completing.
+Semantics every implementation must honor (contract details in the class JSDoc): binding calls bridge complete lossless-JSON arguments and resolutions with no seam-level byte cap; the program is treated as a hostile peer (arbitrary binding names are own properties, malformed traffic never crashes the host); no state survives between runs; disposal terminates in-flight runs AND awaits their exit before completing.
 
 ## Vocabulary
 
-`CodeRunRequest` (`program`, `bindings`, `signal?`) carries everything the runtime acts on — defaulting (time budgets, output caps) 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. `CodeRunResult` reports the completion `value?`, ordered capped `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`), 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.
 
 ## Model Experience
 
@@ -31,3 +31,4 @@ No direct invalidation; the named consumer owns any request-prefix changes.
 - **`run()` is one-shot** — `logs` arrive only on the resolved `CodeRunResult`; the seam exposes no streaming-log or progress surface for a live program's output.
 - **A persistent REPL-style kernel is recorded future work** — the no-state-between-runs contract stands until a persistent-kernel backend brings its own logging story ([Code Mode Agent Note](../../../.agents/notes/implemented/feature/2026-06-15-code-mode.md)).
 - **Only the worker-thread backend ships** — `'process'`/`'container'` are declared well-known `isolation` values with no implementation; a hard security boundary awaits a container backend.
+- **Intermediate binding values have no byte cap** — implementations remain subject to structured-clone cost and process memory, while a provider or executor may already have imposed its own acquisition bound.

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

@@ -10,6 +10,7 @@ import type { CodeRunRequest, CodeRunResult } from './types.ts'
 export type {
   CodeBindingFunction,
   CodeBindingNamespace,
+  CodeJsonValue,
   CodeRunFailure,
   CodeRunRequest,
   CodeRunResult,

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

@@ -9,12 +9,16 @@
 /**
  * One host-side function exposed to the program as an async callable. The
  * runtime bridges calls to it (possibly across a serialization boundary), so
- * `args` and the resolution value MUST be structured-cloneable; a runtime
- * rejects a non-cloneable value with a descriptive error rather than
- * corrupting the run. A rejection of this function surfaces inside the
- * program as a rejection of the corresponding call.
+ * `args` and the resolution value MUST be lossless JSON. A runtime rejects a
+ * lossy or non-cloneable value with a descriptive error rather than corrupting
+ * the run. No seam-level byte cap applies to a binding resolution. A rejection
+ * of this function surfaces inside the program as a rejection of the
+ * corresponding call.
  */
-export type CodeBindingFunction = (args: unknown) => Promise<unknown>
+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 }
 
 /**
  * A named group of {@link CodeBindingFunction}s the runtime exposes to the
@@ -63,10 +67,12 @@ export interface CodeRunRequest {
  * - `'timeout'` — an implementation-owned budget expired; the message says which.
  * - `'abort'` — {@link CodeRunRequest.signal} fired.
  * - `'worker-exit'` — the execution substrate died without settling (e.g. OOM).
+ * - `'invalid-output'` — the completion value was not lossless JSON.
+ * - `'output-limit'` — the serialized outer logs/value/diagnostic exceeded the configured cap.
  */
 export interface CodeRunFailure {
   /** The failure class (see the interface doc for each kind's meaning). */
-  kind: 'exception' | 'timeout' | 'abort' | 'worker-exit'
+  kind: 'exception' | 'timeout' | 'abort' | 'worker-exit' | 'invalid-output' | 'output-limit'
   /** Human-readable detail, suitable for feeding back to a model to self-correct. */
   message: string
 }
@@ -79,12 +85,12 @@ export interface CodeRunFailure {
 export interface CodeRunResult {
   /**
    * The program's completion value (its top-level `return`), when it ran to
-   * completion and the value survived the runtime's serialization boundary;
-   * a non-transferable value is replaced by a string rendering, and a failed
-   * or value-less run leaves this absent.
+   * completion and the value crossed the runtime's lossless-JSON boundary.
+   * Invalid or over-limit completions fail the run instead of substituting a
+   * rendered string; a failed or value-less run leaves this absent.
    */
-  value?: unknown
-  /** Text the program emitted, in order (capped by the implementation). */
+  value?: CodeJsonValue
+  /** Text the program emitted, in order, bounded only as part of the outer result. */
   logs: string[]
   /** Present iff the run failed; see {@link CodeRunFailure} for the taxonomy. */
   error?: CodeRunFailure

packages/code-runtime/code-runtime/tests/service.spec.ts

@@ -45,7 +45,7 @@ describe('CodeRuntime service seam', () => {
     const calls: unknown[] = []
     const result = await runtime.run({
       program: 'return 1',
-      bindings: [{ global: 'tools', functions: { probe: async args => void calls.push(args) } }],
+      bindings: [{ global: 'tools', functions: { probe: async (args) => { calls.push(args); return null } } }],
     })
     expect(result).toEqual({ logs: [] })
     expect(calls).toEqual([{ from: 'stub' }])