---
phase: 05-partial-execution-engine
plan: 01
subsystem: workflow
tags: [serde, camelCase, pause-reason, retryable, pub-crate, proptest]

# Dependency graph
requires:
  - phase: 04-workflow-task-bridge
    provides: WorkflowPromptHandler, ExecutionContext, WorkflowStep, StepStatus enum
provides:
  - PauseReason enum with 4 variants (UnresolvableParams, SchemaMismatch, ToolError, UnresolvedDependency)
  - WORKFLOW_PAUSE_REASON_KEY constant for task variable storage
  - WorkflowStep.retryable field with builder and accessor
  - pub(crate) visibility on ExecutionContext and 9 WorkflowPromptHandler helper methods
affects: [05-partial-execution-engine plan 02, task_prompt_handler]

# Tech tracking
tech-stack:
  added: []
  patterns: [internally-tagged serde enum with camelCase, pub(crate) composition pattern]

key-files:
  created: []
  modified:
    - crates/pmcp-tasks/src/types/workflow.rs
    - src/server/workflow/workflow_step.rs
    - src/server/workflow/prompt_handler.rs

key-decisions:
  - "PauseReason uses serde tag='type' with rename_all='camelCase' for MCP-compatible JSON"
  - "retryable field placed on WorkflowStep (not tool definition) -- workflow author knows which steps are transient"
  - "Visibility-only changes on prompt_handler.rs -- zero method body or control flow modifications"

patterns-established:
  - "Internally-tagged enum with camelCase: #[serde(tag = 'type', rename_all = 'camelCase')] for typed discriminated unions"
  - "pub(crate) composition: expose internals for sibling modules without public API surface"

requirements-completed: [EXEC-01, EXEC-02, EXEC-03, EXEC-04]

# Metrics
duration: 5min
completed: 2026-02-22
---

# Phase 5 Plan 1: Execution Foundations Summary

**PauseReason enum with 4 typed variants for execution pause reporting, WorkflowStep retryable hint, and pub(crate) on WorkflowPromptHandler internals for composition**

## Performance

- **Duration:** 5 min
- **Started:** 2026-02-22T23:42:24Z
- **Completed:** 2026-02-22T23:47:25Z
- **Tasks:** 2
- **Files modified:** 3

## Accomplishments
- PauseReason enum with 4 variants serializing to camelCase JSON with type tag discrimination
- WORKFLOW_PAUSE_REASON_KEY constant for storing pause reasons in task variables
- WorkflowStep retryable field (default false) with chainable builder and accessor
- ExecutionContext and 9 WorkflowPromptHandler helpers opened to pub(crate) for Plan 02 composition
- 6 unit tests + 1 property test for PauseReason, all 159 existing workflow tests pass unchanged

## Task Commits

Each task was committed atomically:

1. **Task 1: Add PauseReason enum and WORKFLOW_PAUSE_REASON_KEY** - `c7f6561` (feat)
2. **Task 2: Add retryable field and open WorkflowPromptHandler internals** - `ee0be49` (feat)

## Files Created/Modified
- `crates/pmcp-tasks/src/types/workflow.rs` - PauseReason enum, WORKFLOW_PAUSE_REASON_KEY constant, unit tests, property tests
- `src/server/workflow/workflow_step.rs` - retryable field with builder method and accessor
- `src/server/workflow/prompt_handler.rs` - pub(crate) on ExecutionContext and 9 helper methods

## Decisions Made
- PauseReason uses `#[serde(tag = "type", rename_all = "camelCase")]` producing `{"type": "toolError", "failedStep": ...}` style JSON, matching CONTEXT.md locked decisions
- retryable field placed on WorkflowStep (not tool definition) because the workflow author knows which steps experience transient failures
- All prompt_handler.rs changes are visibility-only -- zero method body or control flow changes to maintain the composition constraint from Phase 4

## Deviations from Plan

None - plan executed exactly as written.

## Issues Encountered
- Pre-existing clippy warnings in `pmcp-macros` and `mcp-preview` crates (unrelated to changes) -- out of scope per deviation rules
- Pre-existing flaky property test `fresh_task_record_is_not_expired` in pmcp-tasks (TTL overflow edge case) -- out of scope

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

## Next Phase Readiness
- PauseReason types ready for TaskWorkflowPromptHandler to use in Plan 02
- pub(crate) helpers on WorkflowPromptHandler ready for composition in Plan 02
- WorkflowStep.retryable field ready for execution engine to consult during tool error handling

---
*Phase: 05-partial-execution-engine*
*Completed: 2026-02-22*
