fix(module): surface tool errors as throwable exceptions in sandbox

[Mat4m0]

The problem

Tool errors are opaque and uncatchable in code mode

When a tool returns isError: true, the dispatch function returns the error text as a regular value. The sandbox code has no way to distinguish an error from a successful string result, and try/catch never fires. Structured error details from structuredContent are also lost.

try {
  await codemode.delete_item({ id: "nonexistent" });
} catch (e) {
  // Never reached — error returned as plain string "Item not found"
}

Root cause

buildDispatchFunctions() passed isError results through the same text extraction path as successes, losing the error signal.

Solution

Dispatch side (index.ts): When result.isError is true, return a { __toolError, message, tool, details } sentinel object instead of extracting text. details carries result.structuredContent when available.

Sandbox side (executor.ts): The rpc() proxy detects the __toolError sentinel and throws a structured Error with .tool, .isToolError, and .details properties — making tool errors catchable with try/catch.

try {
  await codemode.delete_item({ id: "nonexistent" });
} catch (e) {
  e.isToolError // true
  e.tool        // "delete_item"
  e.message     // "Item not found"
  e.details     // { ok: false, error: { ... } } (if structuredContent present)
}

Note: Depends on #207 for structuredContent passthrough on success results. This PR only adds error handling.

Files changed

File	What changed
index.ts	buildDispatchFunctions(): check isError → return __toolError sentinel with details; export for testing
executor.ts	Sandbox rpc() proxy: detect __toolError, throw structured Error
codemode.test.ts	5 new tests covering error dispatch

Test coverage

5 new tests in test/codemode.test.ts:

• __toolError sentinel for isError results
• structuredContent included as details in error sentinel
• No details when no structuredContent
• Non-error results unaffected
• isError + structuredContent prioritizes error over structured data

All 150 tests pass (20 test files).

Test plan

• pnpm test passes (150/150)
• pnpm lint passes
• tsc --noEmit passes
• Tool returning isError: true → sandbox throws structured Error with .tool, .isToolError, .details
• Tool returning isError: true + structuredContent → error sentinel includes details
• Non-error tools unaffected by the change

AI tools used

• Claude Opus 4.6

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[pkg-pr-new]

npm i https://pkg.pr.new/@nuxtjs/mcp-toolkit@208

commit: 5945ca9