docs/DESIGN.md

Notestack: Design Doc

Status: draft v0.1 (2026-09-22) Owner: Firebird Technologies

Note: Section 0 of the product brief was not included in the handoff. This doc reconstructs the product framing from Sections 5 to 12 plus the kickoff decisions. Replace Section 1 with the original Section 0 text when available.

1. Product

Notestack turns a writer's archive (Substack, Ghost, Medium, any RSS feed or URL) into a grounded research notebook and a launch engine. Writers can:

• Ask questions of their own archive and get answers with citations to their posts.
• Generate a two-host audio overview of a post or notebook (ElevenLabs).
• Generate videos (explainer 16:9, vertical short 9:16, audiogram 1:1) rendered with Remotion.
• Generate a Launch Kit per post: threads, LinkedIn, Substack Notes, Bluesky, hooks, SEO pack, quote cards, carousels, all in the writer's own voice.
• Schedule everything on the Launchpad calendar and resurface evergreen posts.

Every factual statement Notestack generates must trace back to the writer's own sources.

2. Kickoff decisions

Area	Decision
Backend	FastAPI + SQLAlchemy 2 + Alembic (same stack as blog2video)
Worker	arq on Redis (async jobs, progress events over Redis pub/sub, SSE to clients)
Database	Postgres 16 (no vector extension)
Frontend	React + Vite + TypeScript, plain CSS with design tokens
Renderer	Node service running Remotion (renderer/)
Storage	Cloudflare R2 (S3 API) for raw HTML, audio, video, stills, compiled DSPy programs
Email	Resend, behind a provider interface (mirrors blog2video EmailService)
Auth	Google sign-in + email 6-digit code signup + password login, JWT access/refresh with token_version revocation (mirrors blog2video)
LLM	Provider agnostic through DSPy + LiteLLM. Default Z.ai GLM-5.3 (fast tier GLM-5.3-Flash) via its OpenAI compatible endpoint. Retrieval is agentic search over a file system corpus, not embeddings (see 3.2). Any LiteLLM model string works by env var.
Billing	Three tiers defined in code (app/services/plans.py). BILLING_ENABLED=false for now: everyone gets the top tier limits free, checkout returns 409, pricing page shows "Free during early access".
Blog	Typed blogPosts.ts content array, /blogs and /blogs/:slug, same shape as blog2video

3. Architecture

            +-------------------+        SSE / REST        +--------------------+
 browser -->|  frontend (Vite)  |------------------------->|  api (FastAPI)     |
            +-------------------+                          |  auth, notebooks,  |
                     ^                                     |  billing, storage  |
                     | presigned GET                       +---------+----------+
                     |                                               | enqueue (arq)
            +--------+----------+                          +---------v----------+
            | Cloudflare R2     |<-------------------------|  worker (arq)      |
            | notestack-assets  |   put objects            |  ingest, corpus,   |
            +--------+----------+                          |  DSPy, TTS         |
                     ^                                     +---------+----------+
                     | upload final render                           | POST /render
            +--------+----------+   progress callbacks     +---------v----------+
            | renderer (Remotion)|------------------------>|  api /internal/... |
            +-------------------+                          +--------------------+
     Postgres (api, worker)        Redis (queue, pub/sub, cache)

3.1 Storage pipeline (R2)

All binary and large text payloads live in R2. Postgres stores only keys and metadata.

Key layout (app/services/storage.py::keys):

ws/{workspace_id}/sources/{source_id}/documents/{document_id}/raw.html
ws/{workspace_id}/corpus/manifest.json                           path -> sha256 of every corpus file
ws/{workspace_id}/corpus/INDEX.md                                one line per post
ws/{workspace_id}/corpus/sources/{site}/{date}-{slug}.md         clean post as markdown
ws/{workspace_id}/uploads/{upload_id}/{filename}
ws/{workspace_id}/artifacts/{artifact_id}/{variant}.{ext}      audio, video, stills
ws/{workspace_id}/tts-cache/{sha256(script|voice|settings)}.mp3
system/dspy/{module}/{version}.json                              compiled programs

Flows:

1. Server writes (ingestion, TTS, compiled programs): worker calls storage.put_bytes().
2. Browser uploads (logos, voice consent samples): POST /api/storage/uploads returns a presigned PUT URL and an upload_id; the browser PUTs directly to R2; POST /api/storage/uploads/{id}/complete verifies with a HEAD request and records size and content type.
3. Renderer writes: renderer receives a presigned PUT URL in the render request, so it never holds R2 credentials.
4. Reads: GET /api/storage/objects/{key} checks workspace ownership and 302 redirects to a presigned GET (default 1 hour). Public stills (quote cards) can later move to a public bucket with a custom domain.

The storage service is an S3 client with R2's endpoint, so MinIO in docker-compose stands in for R2 locally with zero code changes.

3.2 Research corpus: file system instead of embeddings

Each post is one markdown file (front matter, # Title, ## Section headings) and the workspace has an INDEX.md with one line per post. Research is an agent loop (dspy.ReAct, app/pipeline/research.py) with three tools scoped to the notebook's files (app/corpus.py):

Tool	Does
list_files(contains)	Index lines for the notebook's posts: date, path, title, headings
search(pattern, path)	Case insensitive regex grep, returns path:line: text
read(path, start_line, end_line)	Numbered lines, 160 per call

The model searches with several phrasings, reads around the hits, and answers with citations of the form (path, line_start, line_end). Before anything reaches the writer, every citation is read back from the file: citations that point outside the notebook, past the end of a file or at empty lines are dropped, markers are renumbered, and an answer left with no verified citation is replaced by "not in your posts". The UI streams each step ("Searching for pricing|paid tier", "Reading On pricing, lines 1 to 40").

Why this over embeddings:

• One vendor. Z.ai's international API has no embedding model, and there is no second key, re-embedding job or dimension lock-in.
• Citations are exact line ranges the model actually read, which is stronger grounding than nearest-neighbour chunks.
• Writers' archives are small (hundreds to a few thousand posts, a few MB of text), so grep over local files takes milliseconds.
• The corpus is plain markdown, so the same files feed podcast scripts, launch kits and a future MCP server without conversion.

Trade offs: each question costs several LLM steps instead of one (mitigated by LLM_REASONING_EFFORT=low and the RESEARCH_MAX_STEPS cap), and paraphrase matching depends on the model trying synonyms. If quality or latency needs it later, a Postgres full text index can be added as a fourth tool without changing the corpus.

Storage and sync: R2 holds the corpus under ws/{id}/corpus/ with a manifest.json of file hashes. The worker writes files to R2 and its own cache in one pass. The API calls Corpus.sync() before each research run, which reads the manifest and downloads only changed files into CORPUS_CACHE_DIR. Containers share nothing but R2.

Brief items that assumed embeddings: voice similarity uses the LLM judge alone; the topic map is built from LLM extracted entities per post (Phase 2); resurfacing and SEO internal links search the corpus with the same tools.

3.3 LLM layer

app/llm/provider.py builds a dspy.LM from env:

LLM_MODEL=openai/glm-5.3               # any LiteLLM model string
LLM_FAST_MODEL=openai/glm-5.3-flash    # judges, cleanup, cheap passes
LLM_API_BASE=https://api.z.ai/api/paas/v4
LLM_API_KEY=...
LLM_REASONING_EFFORT=low               # low | high | max

Z.ai considerations baked in:

• OpenAI compatible chat endpoint, so the openai/ LiteLLM prefix plus api_base works.
• GLM-5.x always reasons (thinking cannot be disabled). Every call sends thinking: enabled with reasoning_effort=low by default; modules that benefit (the groundedness judge) ask for main_lm("high"). Reasoning tokens count against max_tokens, so the default is 16K to leave room for the structured answer. Z.ai recommends temperature 1.0 for GLM-5.x.
• 1M token context on GLM-5.3 means whole-notebook prompts (summaries, podcast scripts) can read the files directly; chat uses the research agent to keep citations tight and cost low.
• Tool calling runs through DSPy ReAct, so it works with any provider, not only ones with native function calling.
• Token usage from every call is written to usage_events (metering from day one).

Swapping to Anthropic, OpenAI, Gemini or a local model is only an env change.

3.4 Jobs and progress

Every long operation is a row in jobs (kind, status, progress, error, cost) plus an arq task. Workers publish progress to Redis channel job:{id}; GET /api/jobs/{id}/events streams it as SSE. No API request blocks for more than a few seconds.

4. Data model

Implemented in backend/app/models and alembic/versions/0001_initial.py.

• users, workspaces, workspace_members, subscriptions
• email_verification_codes, update_emails, update_email_sends
• sources, documents (with corpus path), notebooks, notebook_documents
• voice_profiles, voice_consents
• chats, messages, citations (document, path, line range, verified quote)
• artifacts, jobs (covers render_jobs and tts_jobs via kind), uploads
• calendar_items, tracked_links, engagement_events
• dspy_traces, usage_events

5. DSPy program design

See brief Section 6. Signatures live in backend/app/llm/signatures.py with Pydantic output models. Phase 1 ships CleanAndSegment, ResearchArchive (the file research agent) and BuildVoiceProfile. All grounded outputs cite SourceRef(path, line_start, line_end). The rest are stubs with typed signatures so the schema contract is fixed early.

6. Plans

	Free	Writer	Studio
Price (when billing turns on)	$0	$19/mo	$49/mo
Sources	1	3	10
Indexed posts	50	500	5,000
Audio overview minutes / mo	10	60	240
Video render minutes / mo	3	30	120
Launch Kits / mo	5	50	unlimited
Voice profile	yes	yes	yes
Voice cloning (with consent)	no	yes	yes
Brand kit, no watermark	no	yes	yes

While BILLING_ENABLED=false, every workspace resolves to Studio limits.

7. Design system

Strict palette: #000000, #217cff, #FFFFFF and opacity variants only. Tokens in frontend/src/styles/tokens.css. Landing page is a night sky: canvas starfield with slow parallax, small twinkling sparkles, a soft blue nebula haze and a neon horizon line. prefers-reduced-motion renders a static sky. Logo slot (<Logo />) is a white tile that holds the black silhouette mark; drop the final file at frontend/public/logo.svg.

Copy rule: no em dashes anywhere in UI, email or generated output. The generation layer strips them as a last pass (app/llm/postprocess.py).

8. Security and privacy

• JWT access (72h) + refresh, revocation by bumping users.token_version.
• One auth provider per account for life (Google or email), same as blog2video.
• Verification codes hashed, 10 minute TTL, 5 attempts, 60s resend cooldown.
• R2 keys are always workspace scoped; the API checks ownership before presigning.
• No training on user content without opt-in (workspaces.training_opt_in, default false).
• Voice cloning requires a stored consent record with the recorded sample key.