A standalone learning app (web + Electron desktop): a **teacher agent** (Next.js; the Vercel AI SDK's `UIMessage` protocol end-to-end, LLM engine [pi-ai](docs/pi-engine-swap.md) via OpenRouter), probe→teach lessons with graded quiz/ask interactions, a formal **session plan tree** the teacher authors once (`plan_init`) and whose progress is derived from tagged quiz calls, and a persistent cross-session **knowledge graph** of what the learner knows — the graph is the app's home page.
Not a chat app with a graph bolted on: sessions are probe→teach lessons, the plan tree is a structured, schema-validated object, quiz outcomes reach the graph through the extraction pipeline as ledger events, and the graph feeds back as the teacher's session context (semantic top-K under a token budget) so probing compounds across sessions.
- [`docs/architecture.md`](docs/architecture.md) is the **canonical architecture spec** — layers, the import law, the five systems, the invariants, the seam directory. (The pre-audit spec is archived under `docs/archive/` — history only.)
Secrets and machine-specific paths only. Model choice and thinking budgets are the user's, not the environment's — BYOK model slots live in **settings** (`models` section: strong/cheap/vision, provider + model id + optional thinking level; per-role and per-chat overrides ride on top). The extraction batch threshold is a settings knob too (`graph.extractionChunkTokens`, default 4096, floor 500).
Five layers, dependency arrows pointing inward only, machine-enforced as four ESLint zones (shell → barrels only; core and agent never import below themselves). Two composition roots, one writer per store. The full spec — layers, systems, runtime flows, invariants, seams: [`docs/architecture.md`](docs/architecture.md).
**Core invariant:** the extraction pipeline (extractor → auditor → merger) is the sole graph writer — tree-blind and post-hoc, triggered by token coverage, not quiz counts. The LLM stages propose, verify, and judge identity (link-or-create against the current graph; each finding carries verbatim evidence and message-granular provenance); the deterministic merger owns every ledger append and rebuilds anything the model could silently mis-copy (event kinds, timestamps, idempotency refs, provenance) from the transcript. Every node is an objective, world-facing fact; the learner's relationship to it lives entirely in the event ledger. The teacher stays a teacher; everything below the ledgers is derived.
**Client-side question tools.**`quiz` and `ask_user_question` have no server `execute`: the tool call streams to the browser, the learner answers in the dock, the client grades via `question-core` and returns the verdict with `addToolOutput` — which fires the SDK continuation so the teacher resumes mid-turn. Options are shuffled deterministically (seeded by toolCallId) so server and client renders match. A pending quiz persisted in the chat record is exactly what makes **resume mid-question free**.
**The formal plan tree (author-once).** The teacher authors the session's dependency tree with one schema-validated tool — `plan_init`, whose mermaid-subset input is parsed deterministically (line-numbered errors) and validated as a DAG. The tree persists in the chat record; progress is never mutated — `current`/`visited`/upcoming are **derived** from tagged quiz calls in the transcript, and the panel renders that derivation.
**The async sub-agent protocol (ack-and-steer).**`research` / `demo` / `visual` are server-executed tools: the call resolves immediately mid-turn with a fire-and-forget ack and the teacher keeps teaching; a background runner works in parallel (the client polls `/api/activity` and `/api/jobs`). On completion the runner builds a **steer message** — a user-role `UIMessage` whose text part is the model-facing result and whose `data-subagent-artifact` part carries the full result for the client — and the **wake pipeline** delivers it: a per-chat serialized queue waits for the turn to end and no question to be pending, then fires a server-side teacher turn that weaves the result into the lesson. Delivery is exactly-once (deterministic steer ids, delivered-flag checks at every claim point); stalled jobs are recovered on read; aborted jobs deliver an abort steer. The client adopts the wake turn through the same `turnInFlight` machinery as returning mid-stream (busy shimmer, composer gate) and renders steers as artifacts — never a bubble. Sub-agents **verify, never one-shot**: the demo-builder headlessly executes its HTML in system Chrome before delivery; the visual-maker renders each SVG and looks at it (vision-capable model — the `vision` slot in settings).
**The knowledge graph (two channels, one writer).** The write channel: the extraction pipeline — extractor (LLM: sees only the session, rendered as readable markdown by the shared `core/session-markdown.ts` engine — propositions as true statements, `follows`/`supports` edges with verbatim evidence; fully trusted, graph-blind) → auditor (LLM, an agentic loop that never sees the source: explores the existing graph through `find` / `list_sessions` / `list_propositions` tools, stamps each proposition with an identity verdict — link to an existing node (equivalence bias: paraphrases merge) or create — and may draw bridging edges between existing nodes and the new batch) → merger (`mergeFindings`, deterministic: applies the verdicts, link-appends phrasings/provenance, resolves and dedupes edges, checkpoints coverage) → layout settle. No quiz outcomes or understanding assessments live in the graph (2026-09-27 cleanup); assessment becomes practice-module territory. Triggered when a chat's **uncovered tokens** (message-view fingerprints, `coverage.jsonl`) cross `graph.extractionChunkTokens` (a settings knob, default 4096, floor 500 — read fresh per turn); failure checkpoints nothing, the next trigger re-runs. The same pipeline serves the **notes front door** (`POST /api/graph/import`: any `*.md`/`*.txt` becomes a source; re-imports are idempotent by path hash). The read channel: `GET /api/graph` derives the snapshot from the ledgers — a pure read; the home view is a hand-rolled Canvas 2D renderer (one rAF loop, dirty-flag idle, d3-zoom camera, zoom-gated labels, cluster hulls) over a d3-force layout, with server-persisted render settings and drag-committed positions. Clusters are **birth-session groupings**: a node joins the cluster of the session that birthed it (a chat, or an imported notes file as a file-kind session), derived at read — no embedding pass, no naming pass. The teacher reaches the graph on its own terms through the gated prober tools (`list_sessions` / `list_propositions`, the `agent.graphTools` setting) — there is no automatic context injection.
**Dictation.** Optional speech-to-text: the server mints short-lived Deepgram tokens; audio streams browser→Deepgram over WebSocket, never through the server.
All deterministic, no LLM, no network (engines are injected — pi-ai's faux provider scripted per test; `globalThis.fetch` stubbed where transport matters):
The teaching methodology comes from the Obsidian-based POC (`~/Desktop/Obsidian/vault/π/learn`; its `knowledge graph design.md` was the original epistemic-model source, since amended — see the amendments table in `docs/vision.md`). The harness was originally built on the pi agent SDK, pivoted to standalone Next.js + the Vercel AI SDK, and later swapped its LLM engine back to pi-ai while keeping the AI SDK's `UIMessage` as the client protocol ([`docs/pi-engine-swap.md`](docs/pi-engine-swap.md)).
Nothing under `data/` is ever tracked by git. Chats, graph ledgers, jobs, positions, and the settings records are plain files (JSON/JSONL) — inspect them freely; they are the canonical records. The desktop app relocates the whole directory via `LH_DATA_DIR`.
