[cmglezpdev]

What this changes

Adds buildPlaylistPrompt, the pure builder for the playlist-level prompt.md: it instructs the assistant to orchestrate — spawn one subagent per member video (each following that member's own prompt.md into <playlist>/NN-<video>/), then write the root README from the collected reports, listing failed/unavailable members.

Why

One mega-prompt inlining every transcript would blow the assistant's context; per-video prompts with no root document would lose the course-level summary. The orchestrator contract keeps the assistant's main context clean and parallelizes the work (with a sequential fallback stated in the prompt).

How to verify

pnpm typecheck
pnpm vitest run src/domain/prompt --exclude '**/.claude/**'

Read the generated sections in order in build-playlist-prompt.ts: role, Step 1 root folder, Step 2 subagent briefs, Step 3 report collection, Step 4 README (+Not included only when members are missing).

Checklist

• pnpm typecheck and pnpm test pass
• Commits follow Conventional Commits

Scope

• Includes: the builder + 16 substring/path tests (no snapshots).
• Excludes: writing the file to disk (PR 5 of the chain), curation.

Chain Context

Field	Value
Chain	playlist-support
Tracker PR	#40
Position	4 of 6
Base	feat/playlist-support-03a-package-name
Depends on	PR 3 (#43)
Follow-up	PR 5 (orchestrator)
Review budget	374 / 400

Chain Overview

main
 └── #40 tracker: feat/playlist-support
      └── #41 listing → #42 store → 03a packageName → 03b prompt → 04 orchestrator → 05 CLI
          (this PR: 📍 4)