549 Task 02 Session State Decomposition 585c2b8a

Task 02: SessionState Decomposition

Status: PENDING

Depends on: Task 01 ✓ (canonical messaging adopted)

Summary

SessionState remains a single, large structure with mixed concerns and unclear ownership boundaries. The current shape makes it hard to reason about state responsibilities and amplifies coupling across unrelated domains.

Goal: Decompose SessionState into focused sub-structures with clear ownership.

Context

src/tunacode/core/state.py contains 40+ fields including:

• ReAct scratchpad data (react_scratchpad, react_forced_calls, react_guidance)
• Todos (todos)
• Tool call tracking (tool_calls, tool_call_args_by_id)
• Usage metrics (last_call_usage, session_total_usage)
• Messages (messages)
• Agent cache (agents, agent_versions)
• Runtime state (current_iteration, iteration_count, request_id)

Planned sub-structures from PLAN.md:

• ConversationState - messages, token counts
• ReActState - scratchpad, guidance, forced calls
• TaskState - todos, original query
• RuntimeState - iteration tracking, request ID
• UsageState - metrics, cost breakdown

Lessons from Task 01

Task 01 (canonical messaging adoption) established patterns to follow:

1. Adapter Pattern Works

The messaging/adapter.py successfully handles polymorphism between dict and pydantic-ai messages. This same pattern can be applied to state access:

• Create typed accessors for each sub-state
• Hide internal structure from consumers

2. Detection vs Mutation Separation

Task 01 separated:

• Detection → routed through adapter (read-only)
• Mutation → kept in sanitize.py (write operations)

Apply same pattern to state:

• Reading state → typed accessors with validation
• Mutating state → explicit setters with invariant checks

3. Incremental Migration

Task 01 migrated 3 call sites first, then consolidated sanitize.py. Same approach:

• P1: Create sub-structures and typed accessors
• P2: Migrate consumers incrementally

4. LOC Reduction is a Feature

Task 01 deleted ~156 LOC of duplicate accessors. Decomposition should similarly:

• Eliminate scattered field access
• Centralize state invariants
• Remove ad-hoc state manipulation

P1: Analysis & Sub-Structure Design

Scope

Analyze current SessionState usage and design typed sub-structures.

Tasks

Acceptance Criteria

1. All 40+ fields categorized into sub-structures
2. Each sub-structure has clear single responsibility
3. Ownership boundaries documented
4. Migration path identified for each consumer

P2: Decomposition Implementation

Scope

Implement sub-structures and migrate consumers.

Tasks

Acceptance Criteria

1. SessionState uses typed sub-structures
2. All consumers use typed accessors (no direct session.field for internal state)
3. Sub-structures have clear invariants enforced
4. Tests pass (430+)
5. No regression in session persistence/resume

Files to Modify

New Files

• src/tunacode/types/state_structures.py - Sub-structure definitions (or extend canonical.py)

Modified Files

• src/tunacode/core/state.py - Decompose SessionState, add accessors
• src/tunacode/core/agents/main.py - Use typed accessors for ReAct, iteration
• src/tunacode/core/agents/resume/sanitize.py - Use typed accessors for tool tracking
• src/tunacode/ui/app.py - Use typed accessors for session state

Related Docs

• PLAN.md - Overall architecture refactor plan
• Task 01 - Canonical messaging (COMPLETE)
• Architecture Refactor Status
• Canonical Types - Existing type definitions