🤖 refactor: simplify compaction notification tests

[ammar-agent]

Summary

Simplifies the notification/compaction follow-up test surface after #3261 by removing dead ContinueMessage factory code and replacing repeated AgentSession/WorkspaceStore scenario setup with focused fixtures. Net diff removes 1,091 lines while preserving the behavioral coverage for post-compaction notification suppression, background handoffs, queued follow-ups, and legacy pending-follow-up recovery.

Background

#3261 intentionally localized notification policy in the browser aggregator. This follow-up keeps that behavior intact but trims older helper code and test boilerplate that made the related compaction/notification paths harder to review.

Implementation

• Removed unused ContinueMessage builder/rebuilder types and their standalone tautological tests; repo search found no production callsites.
• Refactored agentSession.continueMessageAgentId.test.ts around a shared AgentSession/history harness and semantic compaction-summary fixtures.
• Refactored WorkspaceStore.test.ts background completion scenarios around activity/stream event fixture helpers.
• Updated one stale test comment that still referred to the removed ContinueMessage helper.

Validation

• bun test src/browser/stores/WorkspaceStore.test.ts src/node/services/agentSession.continueMessageAgentId.test.ts src/browser/utils/messages/StreamingMessageAggregator.test.ts src/browser/utils/chatCommands.test.ts
• make static-check

Risks

Low. Production change is limited to deleting unused common-message helper exports. Test refactors keep the same behavioral scenarios but centralize repeated fixture construction, so the main risk is fixture abstraction hiding a future scenario mismatch.

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Generated with mux • Model: openai:gpt-5.5 • Thinking: high • Cost: $66.83

[ammar-agent]

@codex review

Please review this follow-up simplification PR, especially the removal of dead ContinueMessage helpers and the refactored compaction/notification test fixtures.

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 106ea5b802

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[ammar-agent]

@codex review

Addressed the mobile build issue by removing the stale mobile import of the deleted helper and verified mobile tests locally.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🚀

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