feat: honor explicit disabled tool configuration through Runtime

[SaladDay]

Saved and inline Agent configurations previously rejected explicitly disabled web search and programmatic tool calling. This accepts and freezes those declarations, carries the requested control through the common Runtime contract, and enforces native disabling before new or resumed execution. Unsupported enablement rejects; omitted programmatic configuration retains native behavior with the approved official-default difference documented.

Validation:

• Fixed OpenAI SDK 3.13.0 and raw HTTP through independent Core, PostgreSQL and Docker daemons: Codex/Kimi K3, Claude/Kimi K3 and MiniMax Code/MiniMax-M2.7 passed saved/inline configuration, native receipts, SSE/Items, cold continuation with the same native history and tenant isolation.
• Separate native-control evidence, targeted Go race checks, make openapi, server make check excluding the browser target, and local make check-web (73 cases) passed. All make check targets were covered across the two hosts; no DB queries changed.
• Fresh independent GPT-6 Astra high whole-diff review found no actionable findings and independently passed related Go tests. Credential scans found no exposure outside private 0600 configuration.

Live scope is environment:none. Workspace/provider combinations were not requalified; enabled PTC/search and complete hosted default/error compatibility remain open. See contracts/agents-api/tool-policy.md.

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