lvlup-sw/synthesis

Synthesis Skill

VCS Provider

This skill uses VCS operations through Exarchos MCP actions (create_pr, merge_pr, list_prs, check_ci, etc.). These actions automatically detect and route to the correct VCS provider (GitHub, GitLab, Azure DevOps). No gh/glab/az commands needed — the MCP server handles provider dispatch.

Not to be confused with merge_orchestrate. This skill calls merge_pr to land a user-facing PR on main via the VCS provider — a remote operation. merge_orchestrate (@skills/merge-orchestrator/SKILL.md) is the upstream sibling: a local git merge of a subagent worktree branch onto the integration branch during the delegate → merge-pending → delegate HSM loop. Synthesize never invokes merge_orchestrate; merge-pending never invokes merge_pr.

Overview

Submit stacked PRs after review phase completes. The prepare_synthesis composite action consolidates readiness checks, stack verification, test validation, and quality signal analysis into a single call -- eliminating the multi-script coordination that historically caused synthesis failures.

Prerequisites:

• All delegated tasks complete with reviews passed (spec + quality)
• The integration branch already exists from delegation phase
• Task branches present and pushed to remote

Do NOT proceed if either review is incomplete or failed -- return to review first.

Entry points: Synthesis is normally reached from the review phase of feature / debug / refactor workflows. It is also reachable from oneshot workflows via the opt-in path — when a user signals "let's open a PR for this" during plan or implementing, the request_synthesize event is appended, and finalize_oneshot then resolves the choice state and transitions the workflow to synthesize. See @skills/oneshot-workflow/SKILL.md for the opt-in mechanics and synthesisPolicy semantics.

Triggers

Activate this skill when:

• User runs synthesize command
• All reviews have passed successfully
• Ready to submit PRs
• Oneshot workflow resolved to synthesize via finalize_oneshot

Process

Runbook: Follow the synthesis-flow runbook: exarchos_orchestrate({ action: "runbook", id: "synthesis-flow" }) If runbook unavailable, use describe to retrieve action schemas: exarchos_orchestrate({ action: "describe", actions: ["prepare_synthesis"] })

Step 1: Verify Readiness

Call the prepare_synthesis composite action to validate all preconditions in a single operation:

mcp__exarchos__exarchos_orchestrate({
  action: "prepare_synthesis",
  featureId: "<id>"
})

This action performs:

• Phase readiness -- Confirms workflow is in the correct phase with all reviews complete
• Stack integrity -- Detects diverged branches, missing task branches, or broken parent chains and reconstructs automatically
• Test verification -- Runs npm run test:run && npm run typecheck from the stack top
• Benchmark regression -- If state.verification.hasBenchmarks is true, checks for performance regressions
• Quality signals -- Queries code_quality view for regressions and actionable hints
• Gate events -- Auto-emits gate.executed events for each check (tests, benchmarks, CodeRabbit)

For the full breakdown of individual checks the composite action performs, see references/synthesis-steps.md.

On success: All checks passed. The response includes a readiness summary with any quality hints to present to the user. Proceed to Step 2.

On failure: The response identifies which check failed and provides remediation guidance. Follow the guidance -- typically returning to review or delegate.

If any quality hint has confidenceLevel: 'actionable', present the suggestedAction to the user before proceeding.

Step 2: Write and Validate PR Descriptions

For each PR in the stack, write a structured description following references/pr-descriptions.md. Required sections: Summary, Changes, Test Plan, plus a footer. Projects can override required sections via .exarchos/pr-template.md.

Title format: <type>: <what> (max 72 chars)

Write the PR body to a temp file:

cat > /tmp/pr-body.md <<'EOF'
## Summary
[2-3 sentences: what changed, why it matters]

## Changes
- **Component** -- Description of change

## Test Plan
[Testing approach and coverage]

---
**Results:** Tests X pass · Build 0 errors
**Design:** [doc](path)
**Related:** #issue
EOF

Validate before creating the PR:

mcp__exarchos__exarchos_orchestrate({
  action: "validate_pr_body",
  bodyFile: "/tmp/pr-body.md"
})

Do NOT call create_pr until validation passes. If validation fails, fix the body and re-validate.

Step 3: Submit and Merge

Create PRs using the validated body and enable auto-merge. For each branch in the stack (bottom-up):

// Create PR via VCS MCP action
exarchos_orchestrate({
  action: "create_pr",
  base: "<parent-branch>",
  head: "<branch>",
  title: "<type>: <what>",
  body: "<pr-body>"
})

// Enable auto-merge
exarchos_orchestrate({
  action: "merge_pr",
  prId: "<number>",
  strategy: "squash"
})

After submission:

1. Apply benchmark label -- If verification.hasBenchmarks is true, apply label: gh pr edit <number> --add-label has-benchmarks
2. Record PR URLs -- Capture URLs via exarchos_orchestrate({ action: "list_prs", state: "open" })
3. Update state:

mcp__exarchos__exarchos_workflow({
  action: "update", featureId: "<id>", updates: {
    "artifacts": { "pr": ["<url1>", "<url2>"] },
    "synthesis": { "mergeOrder": ["<branch1>", ...], "prUrl": ["<url1>", ...], "prFeedback": [] }
  }
})

For merge ordering strategy, see references/merge-ordering.md.

Human checkpoint: Output "Stacked PRs enqueued: [URLs]. Waiting for CI/merge queue." then PAUSE for user input: "Merge stack? (yes/no/feedback)"

• 'yes' -- PRs merge; transition to completed via cleanup
• 'feedback' -- Route to shepherd [PR_URL] to address comments, then return here
• 'no' -- Pause workflow; resume later with rehydrate

Event Emissions (REQUIRED)

After PRs are created and auto-merge is enabled, emit the stack.submitted event:

mcp__exarchos__exarchos_event({ action: "append", stream: "<featureId>", event: {
  type: "stack.submitted",
  data: {
    branches: ["task-001-branch", "task-002-branch"],
    prNumbers: [101, 102]
  }
}})

During shepherd iterations (CI monitoring loop), emit after each assessment:

mcp__exarchos__exarchos_event({ action: "append", stream: "<featureId>", event: {
  type: "shepherd.iteration",
  data: {
    iteration: 1,
    prsAssessed: 2,
    fixesApplied: 0,
    status: "all-green"
  }
}})

These events are checked by check-event-emissions during workflow validation. Missing emissions will trigger warnings.

Post-Merge Cleanup

After PRs merge, invoke cleanup:

mcp__exarchos__exarchos_workflow({
  action: "cleanup", featureId: "<id>", mergeVerified: true,
  prUrl: ["<url>", ...], mergedBranches: ["<branch>", ...]
})

Then sync: git fetch --prune and remove worktrees.

Anti-Patterns

| Don't | Do Instead | |-------|------------| | Skip review phase | Always run review first | | Force push stack branches | Use normal push | | Delete worktrees before merge | Wait for merge confirmation | | Create PR with failing tests | Ensure review phase passes first | | Run readiness scripts manually | Use prepare_synthesis composite action |

Handling Failures

See references/troubleshooting.md for test failures, PR check failures, merge queue rejections, and MCP tool errors.

Phase Transitions and Guards

For the full transition table, consult @skills/workflow-state/references/phase-transitions.md.

Quick reference: The synthesize → completed transition requires guard pr-url-exists — set synthesis.prUrl or artifacts.pr in the same set call as phase.

Schema Discovery

Use exarchos_workflow({ action: "describe", actions: ["update", "init"] }) for parameter schemas and exarchos_workflow({ action: "describe", playbook: "feature" }) for phase transitions, guards, and playbook guidance. Use exarchos_orchestrate({ action: "describe", actions: ["prepare_synthesis"] }) for orchestrate action schemas.

Completion Criteria

• [ ] prepare_synthesis readiness check passed
• [ ] PR descriptions written per references/pr-descriptions.md
• [ ] PRs created and auto-merge enabled
• [ ] PR links provided to user
• [ ] State updated with PR URLs and merge order