Add deployment-wide E2B or own-node hosted sandbox selection

[SaladDay]

Administrators can select E2B cloud or their own Docker/microsandbox nodes from the paired Core console. The entire deployment uses one provider. Switching requires maintenance, the current configuration generation and confirmed zero retained/pending resources; old node identities and enrollment tokens are retired without rewriting Session history.

E2B uses the official pinned SDK through a packaged helper and the existing five-operation SandboxProvider. It initializes the same daemon/harness/workspace Runtime; daily execution, Files and Artifacts keep their shared path. The account key is administrator-only, write-only and encrypted. The helper and private state are included in Core packaging. Caller-managed self_hosted E2B remains separate.

Validation:

• Actual E2B + Kimi execution for Codex, Claude SDK and MiniMax Code: native files, public Files/Artifacts, cancellation, actual Core restart and continuation, pinned OpenAI SDK 3.13.0 queries, tenant/secret isolation, dirty/stale switch rejection and confirmed cloud cleanup.
• Actual Docker and microsandbox node regression, resource-count responses, old node/token rejection, and clean provider transitions.
• Real missing-helper deployment stays administratively recoverable across restart while refusing hosted creation. A real E2B rejected Create with its response discarded is recoverable by the packaged helper without cloud access.
• Real PostgreSQL/race, Go/Core/daemon, generated SQL/OpenAPI, Runtime/helper, installer, client and Web unit/build checks passed. Two fresh Astra high full-diff reviews and an independent bounded helper review completed.

Full make check was run but is not green: the completed browser gate passed 111/147, with 36 failures in the unchanged agents-lifecycle suite; all sandbox cases passed. Four representative failures reproduced on clean base d3f5504, and the remaining 32 were not individually requalified on that base. The findings are recorded in WEB-TEST-002; unrelated UI repairs are excluded.

Limits: Linux amd64 qualification; this does not publish a new release, qualify Quick Tunnel SSE, or claim complete Agents API compatibility. In-place E2B account-key repair with retained resources is deferred as HOSTING-002: cleanup must finish before revoking/replacing the key. A replacement from another account must not be accepted as proof that old compute disappeared. A manual microsandbox fixture exceeded the supported HOME length and left an unresolved receipt; that baseline cleanup limitation is recorded as HOSTING-003. The supported short-HOME path is tested separately, and the old receipt is not forcibly released. No mixed providers, migration, failover or new execution architecture.

Detailed sanitized evidence: ~/.parsar/acceptance/hosted-provider-selection/qualification.md. Temporary resources are batch-owned; cleanup status is recorded there.

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