---
phase: 05-partial-execution-engine
plan: 02
subsystem: workflow
tags: [execution-engine, pause-reason, batch-write, auto-complete, step-loop]

# Dependency graph
requires:
  - phase: 05-partial-execution-engine
    provides: PauseReason enum, pub(crate) helpers on WorkflowPromptHandler, WorkflowStep.retryable
provides:
  - Active execution engine in TaskWorkflowPromptHandler.handle()
  - PauseReason classification (ToolError, UnresolvedDependency, UnresolvableParams, SchemaMismatch)
  - Batch write of progress + results + pause_reason to task store
  - Auto-complete on full workflow success
  - classify_resolution_failure() for runtime dependency checking
affects: [phase-06-middleware, phase-07-integration-tests]

# Tech tracking
tech-stack:
  added: []
  patterns: [local mirror types for circular-dependency avoidance, batch-write-at-end accumulation]

key-files:
  created: []
  modified:
    - src/server/workflow/task_prompt_handler.rs

key-decisions:
  - "Local mirror types for PauseReason/StepStatus instead of importing from pmcp-tasks (circular dependency avoidance)"
  - "classify_resolution_failure as free function (not method on self) for testability"
  - "Tasks 1 and 2 coalesced into single commit since both modify same file and tests verify the implementation"

patterns-established:
  - "Local mirror types: when crate A depends on crate B but needs B's types, mirror the types locally with identical JSON output"
  - "Batch-write accumulation: collect all state changes in memory, write once at end for consistency"

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

# Metrics
duration: 10min
completed: 2026-02-22
---

# Phase 5 Plan 2: Active Execution Engine Summary

**Active step loop in TaskWorkflowPromptHandler with PauseReason classification, batch state write, and auto-complete -- replacing passive inner.handle() delegation**

## Performance

- **Duration:** 10 min
- **Started:** 2026-02-22T23:49:58Z
- **Completed:** 2026-02-23T00:00:07Z
- **Tasks:** 2 (coalesced into 1 commit)
- **Files modified:** 1

## Accomplishments
- Rewrote TaskWorkflowPromptHandler.handle() from passive delegation to active step loop using inner handler's pub(crate) helpers
- Step results accumulated in memory, batch-written to task store at end (EXEC-01)
- Execution pauses at first unresolvable step with typed PauseReason (EXEC-02)
- Tool errors produce PauseReason::ToolError with retryable flag (EXEC-03)
- classify_resolution_failure() distinguishes UnresolvedDependency from UnresolvableParams (EXEC-04)
- Auto-complete transitions task to Completed when all steps succeed
- 11 unit tests covering all helper functions, PauseReason serialization, and classification logic
- All 161 existing workflow tests pass unchanged

## Task Commits

Each task was committed atomically:

1. **Task 1+2: Rewrite handle() with active execution loop + comprehensive tests** - `2f247b7` (feat)

## Files Created/Modified
- `src/server/workflow/task_prompt_handler.rs` - Complete rewrite: active execution engine with PauseReason classification, batch write, auto-complete, 11 unit tests

## Decisions Made
- Used local mirror types for PauseReason and StepStatus instead of importing from pmcp-tasks. The circular dependency (pmcp-tasks depends on pmcp) prevents direct import. The mirror types produce identical JSON output verified by test `pause_reason_to_value_all_variants`.
- Made `classify_resolution_failure` a free function (not a method on `self`) because it only needs the step definition and statuses, making it independently testable without constructing a full handler.
- Coalesced Tasks 1 and 2 into a single commit because both modify the same file and the tests are integral to verifying the implementation. All 7+ planned tests are present.

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] Circular dependency prevents pmcp-tasks type import**
- **Found during:** Task 1 (handle() rewrite)
- **Issue:** Plan specifies importing PauseReason, StepStatus, WorkflowProgress from pmcp_tasks::types::workflow, but pmcp-tasks depends on pmcp (not the reverse), creating a circular dependency
- **Fix:** Created local mirror types (StepStatus enum, PauseReason enum with to_value()) that produce identical JSON output, plus local WORKFLOW_PROGRESS_KEY, WORKFLOW_PAUSE_REASON_KEY constants
- **Files modified:** src/server/workflow/task_prompt_handler.rs
- **Verification:** `pause_reason_to_value_all_variants` test verifies JSON shape matches pmcp-tasks format
- **Committed in:** 2f247b7

**2. [Rule 3 - Blocking] Tasks 1 and 2 coalesced**
- **Found during:** Task 2
- **Issue:** Task 2 asks to add tests to the `mod tests` block, but the complete file rewrite in Task 1 already included all required tests (removing infer_step_statuses tests, adding 11 new tests)
- **Fix:** Both tasks committed as a single atomic unit since they modify the same file
- **Committed in:** 2f247b7

---

**Total deviations:** 2 auto-fixed (2 blocking)
**Impact on plan:** Both auto-fixes necessary for correct compilation and natural code organization. No scope creep.

## Issues Encountered
- Pre-existing clippy warnings in `mcp-preview` crate (unrelated to changes) -- out of scope
- Pre-existing flaky property test `fresh_task_record_is_not_expired` in pmcp-tasks (TTL overflow) -- out of scope

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

## Next Phase Readiness
- Active execution engine complete with all EXEC requirements satisfied
- Phase 5 is now fully complete (both plans done)
- Ready for Phase 6 (middleware/advanced features) or Phase 7 (integration tests)
- PauseReason JSON shapes verified to match pmcp-tasks serde output for cross-crate compatibility

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