Allow disabling built-in browser access

[D3OXY]

Summary

• add a server-backed Built-in browser setting, enabled by default
• prevent agent sessions from receiving T3 browser MCP access when disabled
• omit T3 browser developer instructions from Codex turns when disabled

Testing

• vp check
• vp run typecheck
• vp test apps/server/src/provider/Layers/ProviderService.test.ts apps/server/src/provider/Layers/CodexSessionRuntime.test.ts packages/contracts/src/settings.test.ts

Settings UI screenshot

Note

Add toggle to disable the built-in browser in server settings

• Adds enableBuiltInBrowser to the ServerSettings schema (default true) and exposes a toggle in the General settings panel.
• When disabled, prepareMcpSession in ProviderService.ts revokes and clears any active MCP session instead of issuing credentials.
• buildCodexDeveloperInstructions in CodexDeveloperInstructions.ts conditionally omits browser tool guidance based on the browserEnabled flag, which is derived from whether an MCP server is configured.
• Behavioral Change: sessions started without a configured MCP server will no longer receive browser tool instructions in the developer prompt.

^{Macroscope summarized 711265f.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR introduces a new user-facing feature to disable built-in browser access, affecting agent runtime behavior and modifying core provider infrastructure. The changes gate a significant capability and warrant human review.

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