Feature: background task queue with cancel, retry, and status history

[slashdevcorpse]

Research-backed TODO

Long-running Codex CLI work should not be tied to a single visible chat turn. A queue gives users a reliable way to monitor, cancel, retry, and resume local runs.

Acceptance criteria

• Represent each Codex run as a tracked task with queued, running, completed, failed, canceled states.
• Support canceling a running process and retrying a failed task with the same prompt/context.
• Persist task state in the local state directory and reconnect UI state after refresh.
• Show task duration, exit status, and linked session message.

Public research basis

• Open SWE is explicitly asynchronous and supports multiple tasks with persistent execution environments.
• OpenHands separates CLI, Local GUI, and cloud experiences for agent execution.
• Open WebUI emphasizes persistent storage and responsive app behavior for long-lived chat workflows.

Non-goals

• No remote worker fleet.
• No parallel workspace writes until conflict handling is designed.

Source set

• OpenAI Codex CLI - local terminal coding agent, installer paths, IDE/desktop context.
• OpenHands - local GUI with REST API + SPA, CLI, cloud collaboration/integrations.
• Aider - repo maps, git integration, image/web context, lint/test loops.
• Continue - source-controlled AI checks as markdown agents in CI.
• Open SWE - isolated sandboxes, AGENTS.md context, curated tools, subagents, Slack/Linear handoff.
• Model Context Protocol servers - tool/server registry pattern, filesystem/git/memory/fetch examples, security warnings.
• Open WebUI - responsive/PWA UI, RAG/web browsing, artifact storage, permissions.
• OpenCode - coding-agent modes, plan/build separation, subagent pattern.
• Cline - autonomous coding agent as SDK, IDE extension, and CLI assistant.
• Roo Code - agent-oriented coding workflow inside the editor.

[slashdevcorpse]

Completed by merged PR #102.