Add Prose format support for pipeline templates

[terraboops]

Summary

Introduces Prose, a declarative orchestration language for defining pipeline templates alongside the existing YAML format. Both formats produce identical internal pipeline structures and are fully interchangeable.

Key Changes

• New Prose parser (trellis/core/prose_parser.py): Lark-based parser that converts .prose files to the canonical pipeline dict. Includes:

  • Indentation-based grammar with explicit INDENT/DEDENT token preprocessing
  • parse_pipeline_prose() to load Prose files
  • emit_pipeline_prose() to serialize pipelines back to Prose format
  • Full roundtrip support (parse → emit → re-parse produces identical dicts)

• Format abstraction layer (trellis/core/pipeline_format.py): Unified interface for loading/saving both formats:

  • detect_format() determines format from file extension
  • load_pipeline() handles both .prose and .yaml/.yml files
  • save_pipeline() writes in either format
  • find_template() searches for templates with format fallback priority

• Web API updates (trellis/web/api/routes/pipelines.py):

  • Updated template loading to discover .prose files alongside YAML
  • Added format parameter to template creation
  • Refactored to use new format abstraction layer

• CLI command (trellis/cli.py): New pipelines-to-prose command to batch-convert existing YAML templates to Prose format with optional dry-run mode

• Frontend updates (trellis/web/frontend/templates/):

  • Format selector in pipeline creation UI (YAML/Prose radio buttons)
  • Format badge display in template listings
  • Format indicator in pipeline detail view

• Documentation (docs/, README.md): Comprehensive examples of both formats with side-by-side comparisons and conversion guidance

• Tests: Full test coverage for parser, emitter, and format detection with roundtrip validation

• Dependencies: Added lark>=1.1 for parsing

Implementation Details

• Prose syntax uses indentation-based structure with keywords: pipeline NAME:, session:, gate:, parallel:, description:
• Parser converts Prose to the same canonical dict as YAML: {name, description, agents, post_ready, parallel_groups, gating}
• Format detection is automatic based on file extension; both formats coexist in the same directory
• Template loading prioritizes .prose over .yaml/.yml when multiple formats exist for the same name
• All existing YAML functionality remains unchanged; this is purely additive

https://claude.ai/code/session_01VuaBTgXWpJs7GWdPCMiMRv