Add selected-plugin precedence and attribution to the MCP catalog

[jif-oai]

Why

In short: this PR resolves already-discovered MCP registrations. It does not read selected plugins or discover their MCP servers.

The resolved MCP catalog currently builds config and auto-discovered plugin registrations before runtime contributors are applied. A thread-selected plugin needs a distinct precedence tier in that same initial resolution pass: otherwise a disabled lower-precedence winner can leave stale name-level state behind, and the winning MCP tools cannot be attributed to the selected package reliably.

This PR adds that catalog boundary before executor discovery is connected.

What changed

• Added an explicit selected-plugin registration tier between auto-discovered plugins and explicit config.
• Collected selected-plugin contributions before the initial catalog build, while leaving compatibility and generic extension overlays in their existing runtime phase.
• Retained the winning plugin ID and display name directly on plugin-owned catalog registrations.
• Derived MCP tool provenance from the winning catalog entry instead of joining against local-only plugin summaries.
• Retained the winning selected server's tool approval policy in the running connection manager, so a selected registration cannot inherit approval behavior from a losing local plugin.
• Kept remembered approval session-scoped for selected plugins until there is an authority-aware persistence contract; Codex will not write approval back to an unrelated local plugin.
• Preserved existing name-level disabled vetoes for discovered plugins and config, while keeping a selected package's own disabled registration scoped to that registration.
• Preserved deterministic selection order and existing config, compatibility, and extension precedence.

The resulting order is:

auto-discovered plugin
  < selected plugin
  < explicit config
  < compatibility registration
  < extension overlay

Behavior and scope

This is a catalog and provenance change only. No production host contributes selected-plugin MCP registrations yet, so existing local MCP behavior remains unchanged.

The stacked follow-up, #27870, installs the executor plugin provider that produces these registrations. App-server activation remains a separate final step.

Verification

Focused tests cover precedence, deterministic selected-plugin conflicts, disabled-veto behavior across catalog phases, managed requirements before selected-plugin resolution, winning-server approval policy, and attribution when local and selected packages share an ID or server name. CI owns execution of the test suite.

[jif-oai]

@codex review

[chatgpt-codex-connector]

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