diff --git a/docs/08-handoff.md b/docs/08-handoff.md
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@@ -50,6 +50,7 @@ If you need to create a new restore point:
 
 - Status and counts: `STATUS.md`
 - Project status (narrative): `docs/09-project-status.md`
+- Zero-context explainer: `docs/20-iftypeset-zero-context-explainer.md`
 - Architecture: `app/ARCHITECTURE.md`
 - CLI contract: `app/CLI_SPEC.md`
 - External evaluation prompt: `docs/05-external-evaluation-prompt.md`
diff --git a/docs/20-iftypeset-zero-context-explainer.md b/docs/20-iftypeset-zero-context-explainer.md
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@@ -0,0 +1,225 @@
+# IF.TYPESET (iftypeset) — zero-context explainer
+
+This document is meant to let a fresh session understand `if.typeset` without any chat history.
+
+## Public surfaces
+
+Product landing page:
+https://infrafabric.io/if/typeset/
+
+Forgejo repo:
+https://git.infrafabric.io/dannystocker/iftypeset
+https://git.infrafabric.io/dannystocker/iftypeset.git
+
+## What it is (black/white)
+
+Verified:
+
+- A spec-driven **Document CI** pipeline: Markdown → deterministic HTML/CSS → PDF render → post-render QA → reports + exit codes.
+- A machine-readable **rule registry** (rules are paraphrased + pointer refs; no book text).
+- Default PDF renderer is **Playwright**; Chromium CLI rendering is **banned**.
+
+Not promised:
+
+- Not a fact checker, citation verifier, or “trust” oracle.
+- Not a geometry-perfect PDF validator (PDF QA is heuristic).
+- PDF determinism is “given pinned engine + fonts + locale”, not “byte-identical everywhere”.
+
+## Mental model (spec → pipeline)
+
+1) **Spec** defines rules, profiles, QA thresholds, and coverage metadata.
+2) **Profiles** map typographic intent into deterministic render tokens (A4, margins, font stacks, hyphenation, etc.).
+3) **Lint** checks Markdown text/structure and emits deterministic diagnostics.
+4) **Render HTML** produces deterministic HTML+CSS.
+5) **Render PDF** produces a PDF (engine/fonts dependent); renderer metadata is logged.
+6) **QA** scans HTML (and PDF when present) for layout risks and enforces numeric gates.
+7) **Report** emits coverage summaries + an HTML index for review.
+
+## Where truth lives in the repo
+
+- CLI contract: `app/CLI_SPEC.md`
+- Rendering pipeline overview: `docs/17-rendering-pipeline.md`
+- Renderer strategy / determinism knobs: `docs/04-renderer-strategy.md`
+- Pinned runtime (Docker): `docs/15-docker.md`
+- Rule schema: `spec/schema/rule.schema.json`
+- CLI implementation: `src/iftypeset/cli.py`
+- Rendering + fonts contract: `src/iftypeset/rendering.py`
+- QA thresholds: `spec/quality_gates.yaml`
+- Profiles: `spec/profiles/*.yaml`
+- Rules: `spec/rules/**.ndjson`
+
+## Rule registry (what gets enforced)
+
+Rules live as NDJSON records under `spec/rules/**.ndjson` and are schema-validated by `spec/schema/rule.schema.json`.
+
+Key fields:
+
+- `id`: stable identifier (`CMOS.*`, `BRING.*`, or `HOUSE.*`)
+- `source_refs`: **pointers only** (e.g., `CMOS18 §13.93 p828 (scan p850)`), never quotes
+- `category`: taxonomy bucket (links, citations, layout, etc.)
+- `severity`: `must` / `should` / `warn`
+- `applies_to`: `md` / `html` / `pdf` / `all`
+- `enforcement`: `lint` / `typeset` / `postrender` / `manual`
+- `autofix`: `none|rewrite|reflow|suggest` (+ `autofix_notes`)
+- `tags`, `keywords`, `dependencies`, `exceptions`, `status`
+
+Outcome:
+
+- Automated rules generate deterministic diagnostics.
+- Non-automatable rules (tagged `manual_checklist=true`) appear in the manual checklist artifacts.
+
+## Profiles (typographic intent → render tokens)
+
+Profiles are YAML under `spec/profiles/*.yaml`. They set:
+
+- page size/orientation/margins
+- font stacks + size/line-height
+- hyphenation policy
+- code/table/list overflow policies
+- running head (header/footer) template
+- locale defaults and severity overrides
+
+Example:
+
+- `spec/profiles/audit_report.yaml` is tuned for readable A4 review PDFs (12pt baseline, wide margins) and enables strict fonts (`fonts.require_primary: true`).
+
+## QA gates (numeric thresholds)
+
+QA produces incidents (e.g., overflow risk, stranded headings, wrap hazards) and enforces numeric thresholds from `spec/quality_gates.yaml`.
+
+- `--strict` selects stricter thresholds for CI release gating.
+- QA is deterministic for the same inputs, but it is heuristic by design.
+
+## Determinism + render logs (PDF specifics)
+
+- HTML+CSS are deterministic for the same input + profile.
+- PDF output depends on renderer + fonts; `render-log.json` records enough context to audit variance:
+  - engine name + version
+  - warnings/errors
+  - font policy
+  - requested primary fonts and what fontconfig matched (`fc-match`)
+  - embedded PDF fonts (`pdffonts`) when available
+
+## Commands (flow, artifacts, exit codes)
+
+The main CI-friendly entrypoint is:
+
+```bash
+iftypeset run --input <path.md> --out out --profile <profile_id>
+```
+
+### `validate-spec`
+
+Purpose: validate YAML/JSON spec and rule batches.
+
+- Output: `out/spec-validation.json`
+- Exit: `0` ok, `2` config/schema error
+
+### `lint`
+
+Purpose: parse Markdown and emit deterministic diagnostics + manual checklist.
+
+Outputs (typical):
+
+- `out/lint-report.json`
+- `out/manual-checklist.md` and `out/manual-checklist.json`
+- `out/degraded-mode-report.json` (only when degraded triggers)
+
+Exit: `0` ok, `1` fail threshold, `2` config error
+
+### `render-html`
+
+Purpose: deterministic HTML+CSS for a profile.
+
+- Outputs: `out/render.html`, `out/render.css`, `out/typeset-report.json`
+- Exit: `0` ok, `1` degraded without `--degraded-ok`, `2` config error
+
+### `render-pdf`
+
+Purpose: render PDF from deterministic HTML (default engine: Playwright).
+
+- Outputs: `out/render-log.json` plus `out/render.pdf` on success
+- Exit: `0` ok, `2` config error, `3` renderer/tool error
+
+### `qa`
+
+Purpose: post-render QA + gate evaluation (HTML-first; uses PDF when present).
+
+- Outputs: `out/layout-report.json`, `out/qa-report.json`
+- Exit: `0` pass, `1` fail, `2` config error / missing HTML
+
+### `report`
+
+Purpose: coverage report + trust contract + HTML index.
+
+- Outputs: `out/coverage-report.json`, `out/coverage-summary.md`, `out/trust-contract.md`, `out/report/index.html`
+- Exit: `0` ok, `1` coverage floor violated, `2` config error
+
+### `doctor`
+
+Purpose: environment + determinism diagnostics (renderer, Poppler tools, fonts, locale).
+
+- Outputs: `out/doctor.json`, `out/doctor.md`
+- Exit: `0` ok, `2` config error
+
+### `bundle`
+
+Purpose: portable external review tarball + sha256 manifest.
+
+- Outputs: `out/iftypeset-bundle.tar.gz`, `out/bundle-manifest.json`
+- Exit: `0` ok
+
+## Important flags (what they do)
+
+Shared:
+
+- `--spec`: spec root (default `spec`)
+- `--config`: optional `iftypeset.yaml` path
+- `--out`: output directory (default `out`)
+- `--profile`: profile id
+- `--strict`: strict QA/report thresholds
+- `--degraded-ok`: don’t fail degraded mode (where supported)
+
+Rendering:
+
+- `--engine <auto|playwright|wkhtmltopdf|weasyprint>`: PDF engine preference (`auto` → `playwright`; Chromium CLI is banned)
+- `--self-contained`: embed local images as data URIs (useful for review bundles)
+
+Fonts (prevents “12pt but looks tiny” drift due to fallback x-heights):
+
+- `--font-dir <dir>`: extra font directory (repeatable)
+- `--strict-fonts`: fail if primary fonts aren’t available or the PDF embeds fallback fonts
+- Profile knob: `fonts.require_primary: true`
+
+Lint fixing:
+
+- `--fix`, `--fix-mode <suggest|rewrite>`, `--lint-fixed`
+
+Run control:
+
+- `--skip-pdf`: don’t attempt PDF rendering
+- `--require-pdf`: make PDF rendering failure fail the run
+
+## Corporate font workflow (no fallbacks)
+
+1) Put `.ttf`/`.otf` files in a directory you can mount (e.g., `./fonts/`).
+2) Set the profile font family to the real font family name.
+3) Render with strict enforcement:
+
+```bash
+iftypeset run --input <doc.md> --out out --profile audit_report --font-dir ./fonts --strict-fonts
+```
+
+If it fails, inspect `out/render-log.json` (font matches + embedded fonts).
+
+## Quickstart
+
+```bash
+cd /root/ai-workspace/iftypeset
+python3 -m venv .venv && . .venv/bin/activate
+python -m pip install -r requirements.txt
+python -m pip install -e .
+
+iftypeset run --input fixtures/sample.md --out out --profile web_pdf --degraded-ok
+iftypeset report --spec spec --out out
+```