diff --git a/docs/vision-extensibility.md b/docs/vision-extensibility.md
new file mode 100644
index 0000000..f49838f
--- /dev/null
+++ b/docs/vision-extensibility.md
@@ -0,0 +1,98 @@
+# The learning model & the extensibility direction
+
+Owner-ruled 2026-10-02. Brief by design — the master mental model and the
+extensibility philosophy in one place. Product detail lives in
+[`vision.md`](vision.md); this is the frame over it.
+
+## The three-part model
+
+The product is one loop with three organs:
+
+1. **The knowledge world model** — reasoning chains over propositions
+   (`chains.jsonl`, the stored truth). This is the *compressed* form of the
+   learner's understanding: what they hold, structured as it holds together.
+
+2. **Learning sessions install it** — teaching sessions deposit
+   understanding into the model via extraction. But a session installs only
+   a small set of **weak cues**: the contexts in which the knowledge was
+   encountered. Installation alone is not recall.
+
+3. **Practice strengthens recall** — for knowledge to connect at the right
+   moments, the **cue set** that triggers it must be broadened and
+   strengthened. That is practice's entire job. Practice outcomes feed back
+   into the model as **assessment levels** (per-proposition or per-chain —
+   TBD) — a measurable picture of what the learner actually holds — which
+   drive scheduling and the selection of learning activity.
+
+```
+install (sessions) → strengthen cues (practice) → assess (levels)
+        ↑                                              │
+        └────────── schedule next activity ←───────────┘
+```
+
+Consequence: the world model and its levels are **core truth**; anything
+that merely *strategizes* over them is a candidate for optionality.
+
+## Roadmap — where we are (2026-10-02, owner-approved sequence)
+
+Foundations complete: push architecture landed (zero standing polls),
+per-session models, extraction pipeline (chains-primary), practice
+problems v1, coverage UX, tool-result diet. The sequence from here:
+
+1. **[IN PROGRESS] Quick-fixes round** — ask-questions must not collapse
+   in teach phase (quiz only); ESC aborts the turn from a pending
+   question behind a confirm popup (ESC on the popup cancels — no
+   double-abort); confidence-slider prompt rewritten as clean doctrine
+   (design reasoning must not leak into the system prompt). The old
+   practice dictation bug is deliberately UNFIXED (problem sets likely
+   abandoned).
+2. **Adaptive practice** (the main arc) — session-shaped practice reusing
+   the session machinery + quiz tool; input = propositions/chains via the
+   generator dialogue (cluster/nodes); agent writes problems one after
+   another, adapting difficulty to hold learner accuracy ≈ 85%
+   (research-backed target); problem-engineering theory shared with v1;
+   no user-facing problem parameters (they live in the theory for the
+   agent; the learner steers by talking). Design round first: session
+   kind, spawn flow, what the agent receives, adaptation instructions,
+   end conditions, model slot.
+3. **Session compaction** — manual trigger + automatic token threshold
+   (threshold configurable; auto toggleable in settings). Must preserve
+   extraction coverage (compact-covered-only or extract-before-compact —
+   design). Engineer the compaction instructions (what's critical to
+   preserve).
+4. **Module extraction** — the extensibility Stage 1, AFTER adaptive
+   practice proves itself: convert both practice variants (batch sets vs.
+   adaptive sessions) as the real modules the registry/API is shaped
+   from; the loser then gets deleted or demoted. Old-module fate decided
+   empirically here.
+5. **Fun, when wanted** — data view (GitHub-style activity squares,
+   counts, longest chain, accuracy/confidence split by teaching vs.
+   practice, Brier score — calibration error is also review-targeting
+   signal); standalone bare problem generator (cheap once modules exist).
+
+## The extensibility direction (plugin-shaped)
+
+Strong fundamentals, then optional modules — nothing speculative baked into
+the default experience. The reference model is Obsidian's two-tier system:
+**core plugins** (bundled, toggleable, same API as external ones) and
+community plugins (loaded from disk). We adopt the architecture without the
+third-party obligation:
+
+- **Data core, strategies modules.** Ledgers (chains, levels, transcripts)
+  are core; learning strategies — practice variants, schedulers, drills,
+  enrichments — are modules. A module reads the world model + levels,
+  proposes learning activity, reports outcomes back as level signals.
+- **The skeleton** (all plugin systems share it): manifest → deferred
+  activation → registration into extension points (tools, job kinds,
+  settings sections, routes/nav, events) → curated context API → unload.
+  Our DI ports, tool composer, jobs pipeline, settings sections, and events
+  bus already are those extension points, unnamed.
+- **Staged path.** (0) each new feature's wiring concentrated in one
+  composition file; (1) a module registry with built-in toggleable modules —
+  convert a real feature (practice is the candidate) and let the conversion
+  write the API; (2) harden the context from real use, add per-module state;
+  (3) external loader from `data/plugins/` — optional, maybe never needed.
+- **Why:** learning strategies are learner-, subject-, and
+  situation-dependent — the axis along which features must be optional and
+  toggleable; and a stable module API makes each new experiment cheap to
+  build, cheap to drop.
diff --git a/docs/vision.md b/docs/vision.md
index dc431e0..7a98af9 100644
--- a/docs/vision.md
+++ b/docs/vision.md
@@ -2,6 +2,8 @@
 
 Living document. Started 2026-08-22, capturing the current vision and all agreed decisions. Amend as things evolve.
 
+Master frame: the three-part learning model and the extensibility/plugin direction live in [`vision-extensibility.md`](vision-extensibility.md) (2026-10-02).
+
 Prior art: `knowledge graph design.md` in the Obsidian vault (2025-08-20 ideation) — was canonical for the epistemic model; the 2026-09-02 node-theory + construction redesign in §1 amends it further (no misconception nodes, `follows`/`supports`, no taught events, message-granular provenance). This document records what today's decisions **amend** in it, and adds the session-experience and presentation layers the original doc deferred.
 
 ---