fix(agents): tighten Antigravity input contract

[groupthinking]

Summary

Post-merge contract hardening for the optional Antigravity Agent Factory backend added in #1641.

• restricts MCP server names to lowercase ASCII letters and digits, the conservative subset compatible with both Google's prose and its conflicting published regex
• rejects image context because this adapter currently serializes all context into text; native Antigravity image support is not wired here
• adds regression coverage for hyphen/underscore names and image input

Why

Google's Antigravity documentation says names must be “strictly lowercase and alphanumeric,” but prints ^[a-z0-9_-]+$ beside that sentence. Rejecting punctuation avoids depending on the ambiguous edge until the provider clarifies it.

The provider supports images, but this adapter constructs a string-valued input. Accepting image keys would record a direct-media denial policy while silently converting the image reference to text rather than sending actual image content.

Verification

Repository CI is authoritative. Changes are limited to configuration validation and focused unit cases.

Safety boundary

Draft only. No merge, deployment, live Antigravity invocation, billing action, or production mutation.

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Project	Deployment	Actions	Updated
v0-uvai	Canceled	v0	Sep 6, 2026 7:35am UTC

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Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

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