feature-pipeline-abstraction - SKILL.md Agent Skill

name: feature-pipeline-abstraction description: Use when working with pipeline stages, completion strategies, build loop orchestration, or the web GUI for spectre-build user-invocable: false

Pipeline Abstraction System

Trigger: pipeline, stages, completion strategy, build loop, web gui, spectre-build serve Confidence: high Created: 2025-02-03 Updated: 2026-02-08 Version: 2

What is Pipeline Abstraction?

A generic stage-based pipeline system that replaces the hardcoded build→validate cycle. Pipelines are defined in YAML files with configurable stages, completion strategies, and signal-based transitions. Includes a web GUI for visual pipeline editing and live execution monitoring.

Why Use It?

Scenario	Solution
Need more than build→validate (e.g., code review stage)	Define custom pipeline YAML with additional stages
Want visual feedback on pipeline execution	Use `spectre-build serve` for web GUI
Need different completion detection per stage	Use Promise (tag-based) or JSON (structured) completion strategies
Want loops/retries in pipeline (gaps found → rebuild)	Define transition signals that loop back to earlier stages

Architecture

┌─────────────┐    ┌─────────────┐    ┌─────────────┐
│ YAML Config │───▶│   Loader    │───▶│ PipelineConfig │
└─────────────┘    │ (Pydantic)  │    └───────┬─────┘
                   └─────────────┘            │
                                              ▼
┌─────────────┐    ┌─────────────┐    ┌─────────────┐
│   Agent     │◀───│   Stage     │◀───│  Executor   │
│  (Claude)   │    │ (iteration) │    │ (orchestrate)│
└─────────────┘    └─────────────┘    └─────────────┘
                          │
                          ▼
                   ┌─────────────┐
                   │ Completion  │  Promise: [[PROMISE:SIGNAL]]
                   │  Strategy   │  JSON: ```json {"status": "..."}```
                   └─────────────┘

Key Files

File	Purpose
`src/build_loop/pipeline/completion.py`	CompletionStrategy ABC + PromiseCompletion, JsonCompletion, CompositeCompletion
`src/build_loop/pipeline/stage.py`	Stage class - runs iterations, handles transitions
`src/build_loop/pipeline/executor.py`	PipelineExecutor - graph traversal, event emission, before/after stage hooks
`src/build_loop/pipeline/loader.py`	YAML parsing, Pydantic validation, create_default_pipeline() factory
`src/build_loop/server/app.py`	FastAPI app for web GUI
`src/build_loop/server/routes/pipelines.py`	Pipeline CRUD REST API + demo pipeline creation
`src/build_loop/server/routes/execution.py`	Execution control (start/stop/status)
`src/build_loop/server/routes/ws.py`	WebSocket for live event streaming
`src/build_loop/server/static/pipeline-builder.js`	Canvas-based visual editor
`.spectre/pipelines/*.yaml`	Pipeline definitions (created per-project)

CLI Usage

# Legacy mode (still works)
spectre-build --tasks docs/tasks.md --validate

# Pipeline mode
spectre-build --pipeline .spectre/pipelines/full-feature.yaml --tasks docs/tasks.md

# Web GUI
spectre-build serve
spectre-build serve --port 9000 --host 0.0.0.0

Pipeline YAML Format

name: full-feature
description: "Build → Code Review → Validate cycle"
start_stage: build
end_signals: [COMPLETE]

stages:
  - name: build
    prompt: prompts/build.md
    completion:
      type: promise
      signals: [TASK_COMPLETE, BUILD_COMPLETE]
    max_iterations: 10
    transitions:
      BUILD_COMPLETE: code_review
      TASK_COMPLETE: build  # loop for more tasks

  - name: code_review
    prompt: prompts/code_review.md
    completion:
      type: json
      statuses: [APPROVED, CHANGES_REQUESTED]
    max_iterations: 1
    transitions:
      APPROVED: validate
      CHANGES_REQUESTED: build  # loop back

  - name: validate
    prompt: prompts/validate.md
    completion:
      type: json
      statuses: [COMPLETE, GAPS_FOUND]
    max_iterations: 1
    transitions:
      GAPS_FOUND: build  # loop back

Completion Strategies

Type	Detection	Use When
`promise`	`[[PROMISE:SIGNAL]]` tags in output	Simple signal-based completion
`json`	```json {"status": "..."}``` blocks	Need structured artifacts/metadata
`composite`	Tries multiple strategies	Backward compat (JSON with promise fallback)

Common Tasks

Add a New Stage

Edit pipeline YAML - add stage to stages list
Create prompt template in prompts/ directory
Define completion strategy (promise or json)
Add transitions from/to the new stage
Test with spectre-build --pipeline your-pipeline.yaml --tasks test.md

Create Custom Completion Strategy

# In pipeline/completion.py
class MyCompletion(CompletionStrategy):
    def evaluate(self, output: str, exit_code: int) -> CompletionResult:
        # Parse output, return CompletionResult
        return CompletionResult(
            is_complete=True,
            signal="MY_SIGNAL",
            artifacts={"key": "value"}
        )

Dependencies

# pyproject.toml
dependencies = [
    "fastapi>=0.109.0",
    "uvicorn[standard]>=0.27.0",
    "pyyaml>=6.0",
    "pydantic>=2.0",
    "websockets>=12.0",
]

After pipx install, inject dependencies:

pipx inject spectre-build 'uvicorn[standard]' fastapi pyyaml pydantic websockets

Gotchas

Pipelines are CWD-relative - Server looks for .spectre/pipelines/ in current working directory, not package directory
Demo pipelines auto-create - If no pipelines exist, server creates demo-build-validate.yaml and demo-full-feature.yaml
Regex in JS - Avoid character classes with Unicode arrows (e.g., [→->] is invalid). Use (?:→|->|=>) instead
Dependencies after reinstall - pipx install -e . --force clears injected deps, must re-inject