fix(server): auto-unwrap z.object() schemas in server.tool()

[giulio-leone]

Problem

When z.object({...}) is passed as inputSchema to server.tool(), the SDK silently interprets it as ToolAnnotations instead of an input schema. The tool registers with empty parameters and arguments are stripped without any error.

This is because isZodRawShapeCompat() correctly identifies ZodObject instances as not raw shapes (they have internal _def/_zod properties, not field schemas as values). But the fallback branch at line 1026 unconditionally treats any remaining object as ToolAnnotations.

Root Cause

if (isZodRawShapeCompat(firstArg)) {
    inputSchema = rest.shift();       // z.object({...}) fails this check
} else if (typeof firstArg === 'object') {
    annotations = rest.shift();       // ← z.object({...}) silently lands here
}

Fix

Added extractZodObjectShape() that detects ZodObject schemas (both Zod v3 and v4) by checking for a .shape property whose values are Zod type instances. When detected, the raw shape is extracted and used as inputSchema.

Both forms now work identically:

// Raw shape (always worked)
server.tool('test', { message: z.string() }, handler);

// ZodObject (now also works)
server.tool('test', z.object({ message: z.string() }), handler);

Tests

• Added test for z.object() auto-unwrap with schema verification and argument passing
• Added test for z.object() combined with annotations
• All 1551 tests pass (2 consecutive clean runs)

Fixes #1291

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commit: 1f12bd3

[giulio-leone]

Friendly ping — CI is green and this is ready for review. Happy to address any feedback. Thanks!