[codex] Make MCP connection startup fallible

[aibrahim-oai]

Why

Required MCP server startup was enforced in Session::new after McpConnectionManager had already created the clients. That split let other manager construction paths bypass the same requirement and exposed manager internals solely so the session could validate them. Keeping required-server readiness in the constructor gives every caller one consistent startup contract.

What changed

• make McpConnectionManager::new return anyhow::Result<Self> and fail when an enabled, required server cannot initialize
• pass the startup cancellation token into the constructor so required-server waits remain cancellable
• propagate constructor failures through resource reads, connector discovery, and MCP status collection
• preserve the active manager and cancellation token when a refreshed replacement fails
• keep required-startup failure collection private and cover the constructor error contract directly

Validation

• updated the focused connection-manager test to assert the complete required-server startup error
• local tests not run; relying on CI

[aibrahim-oai]

This change is part of the following stack:

• [codex] Make MCP connection startup fallible #27261 ◀
  • Keep MCP manager stable across refresh #27291

_{Change managed by git-spice.}

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: c2582110de

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 41dda768e5

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 6385c6b3b2

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: cc2754bbba

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: a48cb410f2

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".