fix: add missing items to DebuggerGetVariables array schema (#24)

[marianfoo]

Summary

Adds the missing mcp.Items(map[string]interface{}{"type": "string"}) to the variable_ids array parameter on the DebuggerGetVariables tool registration.

This is a one-line fix for #24.

Problem

The DebuggerGetVariables tool declares variable_ids as a JSON Schema array but omits the required items property. This produces invalid JSON Schema:

{
  "variable_ids": {
    "type": "array",
    "description": "Variable IDs to retrieve ..."
  }
}

Per the JSON Schema specification, an array type must include items to describe the element type. Without it, OpenAI and any strict JSON Schema validator reject the entire tool set with a 400 error — breaking all tools, not just the debugger.

Fix

 mcp.WithArray("variable_ids",
     mcp.Description("Variable IDs to retrieve (e.g., ['@ROOT'] for top-level, or specific IDs like ['LV_COUNT', 'LS_DATA'])"),
+    mcp.Items(map[string]interface{}{"type": "string"}),
 ),

This matches the pattern already used by all other array parameters in the codebase (GrepObjects.object_urls, GrepPackages.packages, GrepPackages.object_types in handlers_codeintel.go).

Audit

I audited all WithArray calls in the codebase. Results:

File	Parameter	Has Items?
internal/mcp/server.go	DebuggerGetVariables.variable_ids	no (fixed in this PR)
internal/mcp/handlers_codeintel.go	GrepObjects.object_urls	yes
internal/mcp/handlers_codeintel.go	GrepPackages.packages	yes
internal/mcp/handlers_codeintel.go	GrepPackages.object_types	yes

DebuggerGetVariables was the only affected tool.

Verification

• go build ./... — compiles cleanly
• go test ./... — all unit tests pass (including internal/mcp package tests)

ok  	github.com/oisee/vibing-steampunk/internal/mcp	0.355s
ok  	github.com/oisee/vibing-steampunk/pkg/adt	0.550s
ok  	github.com/oisee/vibing-steampunk/pkg/cache	0.345s
ok  	github.com/oisee/vibing-steampunk/pkg/config	0.504s
ok  	github.com/oisee/vibing-steampunk/pkg/dsl	0.665s
ok  	github.com/oisee/vibing-steampunk/pkg/scripting	0.505s

Disclosure

This fix was identified, implemented, and audited with the assistance of an AI (Claude). The root-cause analysis from #24 was used as the starting point. The AI verified the fix compiles and passes all existing tests, and audited the full codebase for similar issues.

Fixes #24

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