don't show multiple spaces for codex single line start message rendering

[Soph]

Before:

SessionStart hook (completed)
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After:

SessionStart hook (completed)
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Note

Low Risk
Low risk: changes only the SessionStart hook message formatting and adds unit tests; no auth, data, or strategy logic is modified.

Overview
Adjusts the SessionStart hook banner to be agent-specific: Codex now receives a single-line Powered by Entire: message (including the empty-repo warning) to avoid awkward spacing/rendering, while other agents keep the existing multi-line banner.

Introduces a small sessionStartMessage helper and expands lifecycle tests to assert the Codex vs default formatting behavior.

^{Reviewed by Cursor Bugbot for commit 8df056f. Configure here.}

[Copilot]

Pull request overview

Updates the session-start hook banner formatting to avoid Codex rendering "\n " indentation as multiple spaces when displayed as a single line, while keeping the existing multi-line banner style for other agents.

Changes:

• Introduces sessionStartMessage(agentName, emptyRepo) to centralize banner formatting and special-case Codex as a single-line message.
• Updates handleLifecycleSessionStart to use the new helper for both normal and empty-repo banners.
• Adds tests to assert Codex uses a single-line banner and non-Codex agents keep the multi-line banner.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
cmd/entire/cli/lifecycle.go	Refactors session-start banner construction; adds Codex single-line formatting helper.
cmd/entire/cli/lifecycle_test.go	Adds assertions for multi-line default banner and new unit tests for Codex single-line banner output.