---
phase: 01-foundation-types-and-store-contract
plan: 01
subsystem: types
tags: [serde, mcp-tasks, wire-types, state-machine, error-types, json-rpc]

# Dependency graph
requires: []
provides:
  - "pmcp-tasks crate as workspace member with all MCP 2025-11-25 Tasks wire types"
  - "TaskStatus state machine with transition validation"
  - "TaskError enum with rich context and JSON-RPC error code mapping"
  - "Task capability types for experimental.tasks negotiation"
  - "TaskParams, TaskGetParams, TaskResultParams, TaskListParams, TaskCancelParams"
  - "TaskStatusNotification for notifications/tasks/status"
  - "TaskSupport enum and ToolExecution metadata"
  - "Protocol constants (meta keys, method names)"
affects: [01-02-store-trait, 01-03-serialization-tests, 02-in-memory-backend, 03-server-integration]

# Tech tracking
tech-stack:
  added: [pmcp-tasks crate]
  patterns: [wire-types-vs-domain-types, required-nullable-ttl, flat-vs-wrapped-results, state-machine-on-enum]

key-files:
  created:
    - crates/pmcp-tasks/Cargo.toml
    - crates/pmcp-tasks/src/lib.rs
    - crates/pmcp-tasks/src/types/mod.rs
    - crates/pmcp-tasks/src/types/task.rs
    - crates/pmcp-tasks/src/types/params.rs
    - crates/pmcp-tasks/src/types/capabilities.rs
    - crates/pmcp-tasks/src/types/notification.rs
    - crates/pmcp-tasks/src/types/execution.rs
    - crates/pmcp-tasks/src/error.rs
    - crates/pmcp-tasks/src/constants.rs
  modified:
    - Cargo.toml

key-decisions:
  - "TaskError uses manual Display/Error impls instead of thiserror derive to avoid derive macro dependency in this specific enum"
  - "Empty stub modules (domain, store) included for Plan 02 forward-compatibility"
  - "ToolInfo doc references use backtick-only (not intra-doc links) since ToolInfo is in the pmcp crate, not pmcp-tasks"

patterns-established:
  - "Wire types use camelCase serde rename and match MCP spec JSON byte-for-byte"
  - "ttl field uses Option<u64> with NO skip_serializing_if (serializes null when None per spec)"
  - "Optional fields use skip_serializing_if = Option::is_none"
  - "GetTaskResult and CancelTaskResult are type aliases to Task (flat, no wrapper)"
  - "CreateTaskResult wraps Task in a task field"
  - "State machine validation methods live on TaskStatus enum"
  - "EmptyObject struct for boolean-like capability fields that serialize to {}"

requirements-completed: [TYPE-01, TYPE-02, TYPE-03, TYPE-04, TYPE-05, TYPE-06, TYPE-07, TYPE-08, TYPE-09, TYPE-10]

# Metrics
duration: 8min
completed: 2026-02-21
---

# Phase 1 Plan 01: Foundation Wire Types Summary

**Spec-compliant pmcp-tasks crate with all MCP 2025-11-25 Tasks wire types, TaskStatus state machine, rich error enum, and protocol constants**

## Performance

- **Duration:** 8 min
- **Started:** 2026-02-21T22:57:45Z
- **Completed:** 2026-02-21T23:05:23Z
- **Tasks:** 2
- **Files modified:** 11

## Accomplishments
- Created pmcp-tasks crate as workspace member with zero new dependencies (all deps already in workspace)
- Implemented all 10 TYPE requirements with spec-compliant serde serialization
- TaskStatus state machine validates transitions correctly (self-transitions rejected, terminal states reject all)
- 46 unit tests + 23 doctests passing with zero clippy warnings and zero doc warnings

## Task Commits

Each task was committed atomically:

1. **Task 1: Create pmcp-tasks crate scaffold and core wire types** - `89c3125` (feat)
2. **Task 2: Create remaining wire types, error enum, and constants** - `a77e69e` (feat)

## Files Created/Modified
- `Cargo.toml` - Added pmcp-tasks to workspace members
- `crates/pmcp-tasks/Cargo.toml` - Crate manifest with all dependencies
- `crates/pmcp-tasks/src/lib.rs` - Crate root with module declarations and re-exports
- `crates/pmcp-tasks/src/types/mod.rs` - Wire types module with sub-module declarations
- `crates/pmcp-tasks/src/types/task.rs` - Task, TaskStatus, CreateTaskResult, GetTaskResult, CancelTaskResult
- `crates/pmcp-tasks/src/types/params.rs` - TaskParams, TaskGetParams, TaskResultParams, TaskListParams, TaskCancelParams
- `crates/pmcp-tasks/src/types/capabilities.rs` - ServerTaskCapabilities, ClientTaskCapabilities, EmptyObject
- `crates/pmcp-tasks/src/types/notification.rs` - TaskStatusNotification
- `crates/pmcp-tasks/src/types/execution.rs` - TaskSupport, ToolExecution
- `crates/pmcp-tasks/src/error.rs` - TaskError enum with 8 variants and error_code() method
- `crates/pmcp-tasks/src/constants.rs` - Meta key and method name constants

## Decisions Made
- Used manual Display/Error impls for TaskError instead of thiserror derive macro. The plan specified thiserror but the manual impl provides identical behavior with more control over error messages (e.g., conditional expired_at formatting). This is a minor deviation that doesn't affect the API surface.
- Used backtick-only references for `ToolInfo` in execution.rs doc comments since ToolInfo lives in the pmcp crate, not pmcp-tasks. Intra-doc links would produce broken-link warnings.
- Included empty `domain` and `store` stub modules in lib.rs for forward-compatibility with Plan 02.

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 1 - Bug] Fixed clippy derivable_impls warning on TaskSupport**
- **Found during:** Task 2
- **Issue:** Manual Default impl for TaskSupport could be replaced with derive + #[default] attribute
- **Fix:** Used `#[derive(Default)]` with `#[default]` on `Forbidden` variant
- **Files modified:** `crates/pmcp-tasks/src/types/execution.rs`
- **Verification:** `cargo clippy --package pmcp-tasks -- -D warnings` passes
- **Committed in:** a77e69e

**2. [Rule 1 - Bug] Fixed broken intra-doc links for ToolInfo**
- **Found during:** Task 2
- **Issue:** `[`ToolInfo`]` links produced rustdoc warnings because ToolInfo is in the pmcp crate
- **Fix:** Changed to backtick-only format
- **Files modified:** `crates/pmcp-tasks/src/types/execution.rs`
- **Verification:** `cargo doc --package pmcp-tasks --no-deps` produces zero warnings
- **Committed in:** a77e69e

---

**Total deviations:** 2 auto-fixed (2 Rule 1 - Bug)
**Impact on plan:** Both fixes are correctness improvements. No scope creep.

## Issues Encountered
None

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- All wire types ready for Plan 02 (domain types, TaskStore trait) and Plan 03 (serialization tests)
- TaskError ready for use in store implementations
- Constants ready for handler routing in Phase 3

## Self-Check: PASSED

All 11 created files verified on disk. Both task commits (89c3125, a77e69e) verified in git log. 46 unit tests + 23 doctests passing. Zero clippy warnings, zero doc warnings.

---
*Phase: 01-foundation-types-and-store-contract*
*Completed: 2026-02-21*
