5b4: the README's consumer surface

README.md

@@ -25,38 +25,91 @@ Pure functions, no I/O, no configuration. ADF is the hub: markdown↔HTML compos
 ```ts
 adfToMarkdown(doc: AdfDocument): Result<string>
 markdownToAdf(markdown: string): Result<AdfDocument, ParseError>
-adfToHtml(doc: AdfDocument): Result<string>
-htmlToAdf(html: string): Result<AdfDocument, ParseError>
-markdownToHtml(markdown: string): Result<string>   // via ADF
-htmlToMarkdown(html: string): Result<string>       // via ADF
 isAdfDocument(v: unknown): v is AdfDocument
+
+adfToHtml(doc: AdfDocument): Result<string>               // 0.3.0
+htmlToAdf(html: string): Result<AdfDocument, ParseError>  // 0.3.0
+markdownToHtml(markdown: string): Result<string>          // 0.3.0, via ADF
+htmlToMarkdown(html: string): Result<string>              // 0.3.0, via ADF
 ```
 
 `Result<T>` is `{ ok: true; value: T } | { ok: false; error: ConvertError }` — nothing throws.
-`ConvertError` is `{ code, message, path, position? }`: a code from a closed set, the path of the
-node it names from the document root, and — parsing — a `{ line, offset }` into the string passed
-in, at the start of the line the refused block begins on, `line` counted from 1.
 
-Parsing a source always names where in it the refusal sits, so `markdownToAdf` and `htmlToAdf`
+## The errors
-return the narrowed `ParseError`, whose `position` is there to read without a guard. Every other
+
-direction emits, from a document with no source behind it, and carries `path` alone — including
+An ADF node type this version does not know is not an error: it rides both formats opaquely and
-`markdownToHtml` and `htmlToMarkdown`, where half the refusals come from the emit half.
+restores unchanged (AGENTS.md §3).
+
+`ConvertError` is `{ code, message, path, position? }`. `code` is stable across minors and safe to
+`switch` on exhaustively with no `default`; `message` is free text and may change in any release.
+A parse always names a position, so `markdownToAdf` returns `ParseError` and its `position` reads
+without a guard; an emit reads no source and carries `path` alone; one handler typed on
+`ConvertError` takes both, which is what the composed `markdownToHtml` and `htmlToMarkdown` hand
+back. `path` is the node's place from the document root, alternating `'content'` and an index, so
+`path.map((step) => '/' + step).join('')` is a JSON Pointer at the node — the empty path being the
+document itself.
+
+`position` is `{ line, offset }` into the string passed in: `line` counted from 1, `offset` a
+UTF-16 code unit, a JavaScript string index rather than a codepoint or a byte offset. It points at
+or before the refusal — currently the start of the line the enclosing block begins on; a later
+minor may narrow that, never widen it.
+
+Parsing — `markdownToAdf`, and `htmlToAdf` at `0.3.0`:
+
+| Code | Fires when | What you can do |
+| --- | --- | --- |
+| `malformed-directive` | a `:::` block or `:name[…]` inline directive the grammar cannot read — an unclosed fence or `[content]`, `{attrs}` out of order or duplicated, invalid JSON in an `adf` carry | write the spelling the message names, or escape the line — `\:::` for a block, `\:` for an inline one — to keep it literal text |
+| `malformed-pipe-table` | a pipe row that is no pipe table — a missing or ragged `---` delimiter row, an alignment colon in it, or a row not opening with a pipe | open every row with a pipe and give the delimiter row the header's cell count; a backslash before a pipe keeps it literal text |
+| `unknown-directive-name` | a directive whose name is no node or mark this version spells | check the name in `spec/flavour.md`, or escape the colon; the spelling itself is well formed, so a later minor may give the name meaning |
+| `unmappable-html` | the markdown holds a raw HTML tag, comment or processing instruction | remove it or write it in the flavour — ADF holds no raw-HTML node, and the element mapping lands at `0.3.0` |
+| `unmappable-image` | an image sits inside other content, or carries a title | give the image a paragraph of its own and drop the title, or write the `mediaSingle` directive form |
+
+Emitting — `adfToMarkdown`, and `adfToHtml` at `0.3.0`:
+
+| Code | Fires when | What you can do |
+| --- | --- | --- |
+| `not-an-adf-document` | the value handed in is no ADF document — a missing or wrong `type`, a stray key, a node that is not a node | guard the boundary you receive JSON at with `isAdfDocument`; the message names the branch that refused |
+| `unsupported-document-version` | the document's `version` is not 1 | convert a version-1 document — no markdown spelling carries another |
+
+Either direction — a parse reaches the emitter's own refusals too, asking it which CommonMark
+spelling a node takes:
+
+| Code | Fires when | What you can do |
+| --- | --- | --- |
+| `unspellable-character` | text or a code block holds a carriage return or a null character, which CommonMark rewrites wherever it sits | strip or replace the character; no escape carries it through the round-trip |
+| `unspellable-line-start` | a paragraph line begins with a code span whose backticks would read back as a code fence | put any text before the code span |
+| `unspellable-link` | a link `href` or `title` holds what no canonical escape spells — a backslash, a newline, a control character, an entity reference, an angle bracket beside a space | percent-encode the destination (`%5C` for the backslash, `%26` for the `&` that opens the entity), or drop the title |
+| `unspellable-whitespace` | an `emoji`, `mention` or `status` holds a newline in the text its inline directive spells in the content slot | replace it with a space — an inline directive never spans lines |
+| `unsupported-nesting-depth` | blocks, marks or a carried node's JSON nest past 500 levels | flatten the document; the limit is fixed, and it is what stands between a deep document and a stack overflow |
+| `unsupported-node-shape` | a node carries an attribute, value, argument or body its type does not take — or markdown writes as a directive a node the flavour spells as CommonMark | write the shape the message names; `spec/flavour.md` lists every type's attributes and body |
 
 ## The guarantees
 
 - `markdownToAdf(adfToMarkdown(doc))` equals `doc` — unknown node types included, carried opaquely
   (AGENTS.md §3).
-- `htmlToAdf(adfToHtml(doc))` equals `doc` — fidelity HTML cannot express rides `data-*`
+- Plain CommonMark is valid input to `markdownToAdf` apart from the raw HTML below, with three
-  attributes.
+  carve-outs — literal text matching directive, pipe-table or strikethrough syntax is claimed
-- Plain CommonMark is valid input to `markdownToAdf`, with three carve-outs — literal text
+  (escapable — `spec/flavour.md`) — and one gap: a CommonMark image fits only as its own
-  matching directive, pipe-table or strikethrough syntax is claimed (escapable —
+  title-less paragraph; mid-text and titled images are error results. Converting back yields the
-  `spec/flavour.md`) — and one gap: a CommonMark image fits only as its own title-less paragraph;
+  library's canonical spelling, which round-trips byte-identically.
-  mid-text and titled images are error results. Converting back yields the library's canonical
+- Raw HTML in markdown input is an error result, never a silent drop — a tag, a comment and a
-  spelling, which round-trips byte-identically.
+  processing instruction alike. ADF holds no raw-HTML node; the element mapping ships at `0.3.0`.
-- Foreign HTML maps a documented element set; an unmappable element is an error, never a silent
+- Not every document converts back: `adfToMarkdown` is partial on valid ADF — a text node holding
-  drop. Well-formed HTML only — no tag-soup recovery.
+  a carriage return, a link destination or title no canonical escape spells, a paragraph line
+  beginning with a code span whose backticks read back as a fence. Show the refusal and keep the
+  document read-only; saving markdown you could not produce is the loss the round-trip exists to
+  stop.
+- The pipe table narrows GFM's twice: every row opens with a pipe, so GFM's bare form is an error
+  result rather than the prose it reads as, and an alignment colon in the delimiter row is an
+  error too — ADF holds no column alignment. The trailing pipe is canonical output, optional in
+  input.
+- Past that and `~~`, no GFM: an autolink literal and a `- [ ]` marker stay text, and a checklist
+  is the `taskList` directive.
 - A document nested deeper than 500 levels is an error result, not a stack overflow.
 - The emitted formats are semver surface (AGENTS.md §8).
+- **`0.3.0`** — `htmlToAdf(adfToHtml(doc))` equals `doc`; fidelity HTML cannot express rides
+  `data-*` attributes. Foreign HTML maps a documented element set, an unmappable element is an
+  error, and well-formed HTML only — no tag-soup recovery.
 
 ## Who it is for
 

spec/flavour.md

@@ -1,9 +1,10 @@
 # The markdown flavour
 
 The grammar of the extended markdown `adfToMarkdown` emits and `markdownToAdf` parses. Plain
-CommonMark is a subset with three carve-outs: literal text that matches directive syntax below or
+CommonMark is a subset apart from raw HTML (below), with three carve-outs: literal text that
-reads as a pipe table is claimed by the flavour, and a matched `~~` pair spells `strike` (escape the
+matches directive syntax below or reads as a pipe table is claimed by the flavour, and a matched
-`:`, `|` or `~` to keep it literal) — and one gap: a CommonMark image fits only as its own
+`~~` pair spells `strike` (escape the `:`, `|` or `~` to keep it literal) — and one gap: a
+CommonMark image fits only as its own
 title-less paragraph — mid-text and titled images are named errors. The emitted form is contract
 (AGENTS.md §8). Per-node syntaxes build on this grammar in the sections below.
 

todo-history.md

@@ -392,6 +392,11 @@ Under **3 — `markdownToAdf` (`0.1.0`)**:
       **Settled** (the maintainer, 2026-09-01): ADF's own `A` is "Atlassian", and "converter" is
       the one-way lossy tool §2 exists to replace, where a codec is both directions. It names the
       hub, not the formats around it.
+- [x] **5b — The consumer's error surface (`0.1.0`).** A product-owner read of the public surface
+      found the error result legible to the library and opaque to the consumer holding it, and the
+      README documenting no part of it. The sub-items are that read's answers, and they land before
+      5 because §8 freezes the code list at `0.1.0` and 5b4's table is what reads the list before
+      the freeze closes it.
   - [x] **5b1 — The error's source position.** A parse error names an ADF path into a document the
         caller does not hold yet — `unmappable-html` at `["content", 5]` for a `<span>` on line
         12 — and no coordinate into the markdown string it passed in. `ConvertError` gains an
@@ -455,3 +460,25 @@ Under **3 — `markdownToAdf` (`0.1.0`)**:
         so the emitter escapes that line's first character rather than refusing the document.
         `spec/flavour.md` had two directive blocks inside a container taking no blank line; the
         rule both directions keep is that a pair holding one takes none.
+  - [x] **5b4 — The README's consumer surface.** §8 invites an exhaustive switch on `code` and no
+        code name appears in the README, so it gains a table — code, when it fires, what the
+        consumer does — grouped by direction, over the thirteen names 5b3 settled. Four things a
+        reader who has not opened the code cannot know: raw
+        HTML is core CommonMark and every construct in input is an error until `0.3.0`, which the
+        guarantees' "three carve-outs and one gap" denies and which is the bot and LLM personas'
+        most common failure; `adfToHtml`, `htmlToAdf`, `markdownToHtml` and `htmlToMarkdown` sit
+        unmarked in the code block people copy from, as do the two HTML guarantee bullets, and take
+        a `0.3.0` mark or leave the block; `adfToMarkdown` is partial on valid ADF — a text node
+        holding a carriage return, a link destination no canonical escape spells — which the viewer
+        persona needs told along with
+        what to do about it; and GFM past tables and strikethrough is literal text, task lists
+        taking `:::taskList`. One sentence for the LLM persona: `code` is stable across minors,
+        `message` is free text. The type-level surface freezes at the same moment and gets the same
+        read: what `index.ts` exports and what it withholds, `ParseError` against `ConvertError`
+        where a direction reads a source, and `ConvertFault` staying internal — the README table
+        names the shapes a consumer switches on, so the two audits are one.
+        The direction grouping is read off the call sites rather than the code prefixes, which do
+        not partition by direction: the parser asks the emitter which CommonMark spelling a node
+        takes (§11), so six codes reach a `markdownToAdf` caller as well as an `adfToMarkdown` one.
+        The trailing pipe of a pipe-table row is optional in input, not required; the leading one
+        is what every row must carry.

todo.md

@@ -140,31 +140,11 @@ The numbering is the order the work was planned in, not the order it ships.
       `0.1.0` keeps — 3e names three shapes that parse and then refuse — so the release narrows
       that sentence or lists them.
 - [x] **5a — Rename to `@larvit/adf-codec`.**
-- [ ] **5b — The consumer's error surface (`0.1.0`).** A product-owner read of the public surface
+- [x] **5b — The consumer's error surface.**
-      found the error result legible to the library and opaque to the consumer holding it, and the
-      README documenting no part of it. The sub-items are that read's answers, and they land before
-      5 because §8 freezes the code list at `0.1.0` and 5b4's table is what reads the list before
-      the freeze closes it.
   - [x] **5b1 — The error's source position.**
   - [x] **5b2 — The error messages.**
   - [x] **5b3 — The code list and the flavour's gaps.**
-  - [ ] **5b4 — The README's consumer surface.** §8 invites an exhaustive switch on `code` and no
+  - [x] **5b4 — The README's consumer surface.**
-        code name appears in the README, so it gains a table — code, when it fires, what the
-        consumer does — grouped by direction, over the thirteen names 5b3 settled. Four things a
-        reader who has not opened the code cannot know: raw
-        HTML is core CommonMark and every construct in input is an error until `0.3.0`, which the
-        guarantees' "three carve-outs and one gap" denies and which is the bot and LLM personas'
-        most common failure; `adfToHtml`, `htmlToAdf`, `markdownToHtml` and `htmlToMarkdown` sit
-        unmarked in the code block people copy from, as do the two HTML guarantee bullets, and take
-        a `0.3.0` mark or leave the block; `adfToMarkdown` is partial on valid ADF — a text node
-        holding a carriage return, a link destination no canonical escape spells — which the viewer
-        persona needs told along with
-        what to do about it; and GFM past tables and strikethrough is literal text, task lists
-        taking `:::taskList`. One sentence for the LLM persona: `code` is stable across minors,
-        `message` is free text. The type-level surface freezes at the same moment and gets the same
-        read: what `index.ts` exports and what it withholds, `ParseError` against `ConvertError`
-        where a direction reads a source, and `ConvertFault` staying internal — the README table
-        names the shapes a consumer switches on, so the two audits are one.
 - [ ] **6 — The HTML dialect spec (`0.3.0`).** Element-by-element mapping, the `data-*` fidelity
       scheme, the opaque-carry form, and the documented foreign-element set `htmlToAdf` accepts.
 - [ ] **7 — HTML, ship `0.3.0`.** `adfToHtml`, `htmlToAdf`, the composed `markdownToHtml` /