core: capture request-stable connector runtime tools

[mzeng-openai]

What

• Add the disabled-by-default apps_runtime_state_refactor feature.
• Capture connector runtime state once per model sampling step as one of:
  • legacy live reads when the feature is off;
  • one committed snapshot when available; or
  • an explicitly empty Apps snapshot when no state was committed.
• Substitute captured tools only for the host-owned codex_apps client. Custom MCP clients remain live.
• Preserve the existing read-time tool filter, plugin provenance, server metadata, file-schema shaping, and model-name normalization pipeline.
• Use the same captured tool set for tool exposure, Apps guidance/world state, approval metadata, and app-use analytics.
• Keep full request-stable metadata for delegated Apps approvals in an internal child-session handoff, without adding descriptions or connected-account data to public events.
• Treat account/workspace context discard as stronger than request stability: a captured snapshot is hidden after its owning context is discarded, while same-context refreshes do not rewrite an in-flight step.

Why

This is stack PR 3 of 4, based on #31472. It makes each model request internally consistent while leaving all behavior on the legacy live path unless the feature is explicitly enabled.

Boundaries

• No app-server API change yet.
• No connector-directory metadata fetch during runtime reads.
• No _meta.installedApps dependency.
• Generic filtering, approval, elicitation, and execution stay in McpConnectionManager.
• No separate turn-start availability telemetry is added in this slice.

Checks

• just test -p codex-mcp (118 passed)
• just test -p codex-core delegated_mcp_metadata_handoff_preserves_full_snapshot_metadata
• just test -p codex-core connector_runtime_snapshot_updates_between_sampling_steps
• just test -p codex-core apps_guidance_appears_after_background_recovery_within_a_turn
• just fix -p codex-mcp
• just fix -p codex-core
• just fmt