feat: Persistent task management backed by brainfile

[1broseidon]

Summary

Replaces .cecli/todo.txt with structured task files in .cecli/tasks/board/, powered by the brainfile Python library. The agent and user experience is unchanged — UpdateTodoList is still the only tool, the prompt is untouched, and the ✓/○/→ display is identical.

What users get for free:

• Persistence across sessions — incomplete todos survive session restarts
• History — completed tasks move to .cecli/tasks/logs/ with timestamps
• Power-user access — /task list, /task show, /task complete for humans who want control
• Session resume — get_todo_list() auto-finds incomplete tasks from previous sessions

How it works

UpdateTodoList called →
  get_or_create_session_task() finds/creates task file transparently →
  writes subtasks to .cecli/tasks/board/task-N.md →
  agent sees same <context name="todo_list"> block it always did

The board auto-initializes on first UpdateTodoList call. No explicit setup. No new LLM tools. The agent never knows brainfile exists.

Changes

• cecli/brainfile/store.py — New adapter (~640 lines) over brainfile library. Handles task CRUD, session-task binding, context rendering, TUI bar updates.
• cecli/tools/update_todo_list.py — Collapsed two write paths into one. Always routes through store.
• cecli/coders/agent_coder.py — get_todo_list() always renders from store. Auto-resumes incomplete tasks.
• cecli/commands/task.py — /task commands for power users: list, add, new, show, open, update, delete, complete, drop.
• cecli/sessions.py — Saves/restores active_task_id in session JSON.
• cecli/tools/__init__.py — Removed 7 board-only LLM tools (TaskCreate, TaskList, etc.).
• cecli/tools/utils/registry.py — Removed conditional board-tool gating.
• cecli/tui/widgets/active_task_bar.py — TUI status bar showing active task progress.

Foundation for subagent orchestration

The .cecli/tasks/ directory and brainfile task format also support contracts — structured deliverables, validation commands, and constraints. When subagents land, the parent can create a task with a contract, pass the task ID to the subagent, and the subagent works within that scope. Same files, same library, one-parameter integration: spawn_subagent(task_id="task-2").

Test plan

• 45 tests passing (store, task management, sessions)
• Manual test: fresh session → UpdateTodoList auto-creates board + task
• Manual test: close session → reopen → incomplete todos resume
• Manual test: /task list, /task complete, /task new work as expected
• Manual test: agent prompt unchanged, no mention of brainfile/boards
• Verify no regression on existing UpdateTodoList behavior

Note: Based on v0.97.2 branch per @dwash96's recommendation. Depends on brainfile Python library (brainfile/py) — currently as path dep, will switch to PyPI versioned dep.

🤖 Generated with Claude Code

[1broseidon]

Updates in latest push:

• Fixed all required PR checks — isort, black (line-length 100, preview mode), and flake8 now pass cleanly
• Simplified code and improved code quality — removed unused brainfile imports, hoisted duplicate store construction, cached tab completion for task IDs, consolidated duplicate session title logic, fixed stale column fallbacks
• Removed EPIC/ADR types for the MVP version — create_task now hardcodes type as "task", removed task_type parameter, dropped epic/adr/contract/base schema references from docs. Tasks are the only item type in the initial version.

[1broseidon]

Pulling back while we rethink the task architecture — separating ephemeral scratchpad (UpdateTodoList) from explicit persistent tasks (/task add, CreateTask tool). The current design conflates both into the same task-N namespace which muddies the UX.