baanish · baanish · Aug 15, 2026 · Aug 14, 2026 · Aug 14, 2026 · Aug 14, 2026
diff --git a/AGENTS.md b/AGENTS.md
@@ -23,10 +23,10 @@ Core product traits right now:
 Treat these as core constraints unless the owner explicitly changes the product direction.
 
 - The app is a single exported client-side shell, not a backend product.
-- Artifact payloads live in the URL fragment, using the compact `#<tag><payload>` form where the single tag char identifies the codec: `p` plain, `l` lz, `d` deflate, `a` arx, `b` arx2, `c` arx3, `e` arx4. Legacy `#agent-render=v1.<codec>.<payload>` links (arx-family carry an extra `<dictVersion>.` segment) still decode but are no longer emitted.
+- Artifact payloads live in the URL fragment, using the compact `#<tag><payload>` form where the single tag char identifies the codec: `p` plain, `l` lz, `d` deflate, `a` arx, `b` arx2, `c` arx3, `e` arx4, `f` arx5. Legacy `#agent-render=v1.<codec>.<payload>` links (arx-family carry an extra `<dictVersion>.` segment) still decode but are no longer emitted.
 - The deployed host should not receive artifact contents as part of the initial page request.
 - Supported artifact kinds are `markdown`, `code`, `diff`, `csv`, and `json`.
-- Supported codecs are `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, and `arx4`.
+- Supported codecs are `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, `arx4`, and `arx5`. Auto-emit prefers `arx5`; `arx3` and `arx4` remain decodable.
 - The product is zero-retention by host design, not secret-safe in an absolute sense.
 - Links may still leak through browser history, copied URLs, screenshots, and any future client-side analytics.
 
@@ -84,10 +84,11 @@ The fragment transport is part of the product surface, not an implementation det
 
 Current rules:
 - fragment key: `agent-render` (legacy decode path only; the compact form has no key)
-- emitted format: compact `#<tag><payload>`, where the single tag char identifies the codec (`p` plain, `l` lz, `d` deflate, `a` arx, `b` arx2, `c` arx3, `e` arx4); the compact tag does not carry a dictionary version — arx-family tags imply the build's current dictionary (the build pins the newest supported version and refuses to decode a newer one)
-- legacy format (still decodable, no longer emitted): `agent-render=v1.<codec>.<payload>` for `plain|lz|deflate`, `agent-render=v1.arx.<dictVersion>.<payload>` for `arx`, `agent-render=v1.arx2.<dictVersion>.<payload>` for `arx2`, and `agent-render=v1.arx3.<dictVersion>.<payload>` for `arx3`
-- codecs: `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, and `arx4`
-- `arx4` payloads carry one extra leading char after the tag, the prior id (`m`, `c`, `j`, `s`, or `n`), naming the priming corpus the context mixer ran before the payload; `m`/`c`/`j` additionally need `/arx4-priors.json`, and an encoder that cannot load it emits `s` instead
+- emitted format: compact `#<tag><payload>`, where the single tag char identifies the codec (`p` plain, `l` lz, `d` deflate, `a` arx, `b` arx2, `c` arx3, `e` arx4, `f` arx5); the compact tag does not carry a dictionary version — arx-family tags imply the build's current dictionary (the build pins the newest supported version and refuses to decode a newer one)
+- legacy format (still decodable, no longer emitted): `agent-render=v1.<codec>.<payload>` for `plain|lz|deflate`, `agent-render=v1.arx.<dictVersion>.<payload>` for `arx`, `agent-render=v1.arx2.<dictVersion>.<payload>` for `arx2`, `agent-render=v1.arx3.<dictVersion>.<payload>` for `arx3`, `agent-render=v1.arx4.<dictVersion>.<payload>` for `arx4`, and `agent-render=v1.arx5.<dictVersion>.<payload>` for `arx5`
+- codecs: `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, `arx4`, and `arx5`
+- `arx5` is the emitted mixer codec (ARX 4.5): ARX4's context mixer on ARX2's tuple/overlay pipeline, with every wire scored by honest serialized transport length. `arx3` and `arx4` stay decodable but are no longer auto-emitted because they score dense Unicode by visible character count
+- `arx4`/`arx5` payloads carry one extra leading char after the tag, the prior id (`m`, `c`, `j`, `s`, or `n`), naming the priming corpus the context mixer ran before the payload; `m`/`c`/`j` additionally need `/arx4-priors.json`, and an encoder that cannot load it emits `s` instead
 - fragment size budget: `8192` characters
 - decoded payload budget: `200000` characters
 - Discord markdown link limit: `2000` characters for the full formatted `[label](url)` string; `createGeneratedArtifactLink*` returns `discordMarkdownLinkWarning` when exceeded
@@ -124,7 +125,7 @@ If you change the payload contract, update the code, docs, examples, and the Ope
 - `src/lib/payload/schema.ts` - type surface, limits, fragment key, supported kinds/codecs
 - `src/lib/payload/fragment.ts` - encode/decode logic and transport behavior
 - `src/lib/payload/arx-codec.ts` - arx/arx2/arx3 codecs: dictionary substitution, tuple overlay, brotli, base76/base1k/baseBMP/base64url encoding
-- `src/lib/payload/arx4-codec.ts` - arx4 codec: the arx3 stages with brotli replaced by a deterministic integer context mixer, plus the curated priors it primes on
+- `src/lib/payload/arx4-codec.ts` - arx4/arx5 mixer: the arx2 stages with brotli replaced by a deterministic integer context mixer, plus the curated priors it primes on
 - `public/arx4-priors.json` - curated per-kind arx4 priming corpora (and `.br` pre-compressed variant), regenerated by `scripts/build-arx4-priors.mjs`
 - `public/arx-dictionary.json` - shared substitution dictionary for the arx codec (served as a static endpoint)
 - `public/arx-dictionary.json.br` - pre-compressed brotli variant of the dictionary

diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -9,6 +9,11 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and
 ### Added
 
 - In-viewer edit-and-reshare: open any artifact, correct its content, and generate a new fragment link without leaving the viewer.
+- `arx5` (ARX 4.5): ARX4's context mixer on ARX2's tuple pipeline, scored by honest serialized transport length so Discord and WhatsApp no longer detonate Unicode wires.
+
+### Changed
+
+- Auto-emit no longer selects `arx3` or `arx4`. Existing `#c` and `#e` links still decode.
 
 ## [0.1.0] - 2026-05-05
 

diff --git a/README.md b/README.md
@@ -29,8 +29,8 @@ Built for the OpenClaw ecosystem, `agent-render` focuses on fragment-based shari
 ## Status
 
 - Markdown, code, diff, CSV, and JSON all render in the static shell
-- Fragment transport supports `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, and `arx4`, with automatic shortest-fragment selection across available wire formats
-- The `arx` substitution dictionary is served at `/arx-dictionary.json` with a pre-compressed `/arx-dictionary.json.br` variant; the `arx2` tuple-envelope overlay is served at `/arx2-dictionary.json` with a pre-compressed `/arx2-dictionary.json.br` variant; `arx3` reuses those proven bytes and optimizes for compact visible Unicode fragments; `arx4` adds the curated context-mixer priors at `/arx4-priors.json` with a pre-compressed `/arx4-priors.json.br` variant
+- Fragment transport supports `plain`, `lz`, `deflate`, `arx`, `arx2`, `arx3`, `arx4`, and `arx5`, with automatic shortest-fragment selection across available wire formats. Auto-emit prefers `arx5`; `arx3` and `arx4` remain decodable but are no longer selected
+- The `arx` substitution dictionary is served at `/arx-dictionary.json` with a pre-compressed `/arx-dictionary.json.br` variant; the `arx2` tuple-envelope overlay is served at `/arx2-dictionary.json` with a pre-compressed `/arx2-dictionary.json.br` variant; `arx5` (ARX 4.5) applies the context mixer from `arx4` on top of the `arx2` tuple pipeline and scores every wire by honest serialized transport length; `arx3`/`arx4` stay decode-only because their visible-length Unicode scoring detonates on Discord and WhatsApp. Mixer priors live at `/arx4-priors.json` with a pre-compressed `/arx4-priors.json.br` variant
 - The viewer toolbar copies artifact bodies to the clipboard, downloads them as files, (for markdown) supports browser print-to-PDF, and can edit the open artifact then reshare it as a new fragment link
 - Deployment target: static hosting, including Cloudflare Pages
 

diff --git a/docs/architecture.md b/docs/architecture.md
@@ -98,12 +98,13 @@ The fragment protocol keeps the JSON envelope stable and treats compression stri
 - `deflate` stores deflate-compressed UTF-8 JSON bytes when it outperforms other codecs
 - `arx` applies domain-dictionary substitution, brotli compression (quality 11), and binary-to-text encoding for best-in-class compression. Four wire shapes are candidates: base76 (ASCII, 77 fragment-safe chars), base64url (RFC 4648 `A-Za-z0-9-_` with a `B.` prefix for detection), base1k (Unicode, 1774 chars from U+00A1–U+07FF), and baseBMP (high-density Unicode, ~62k safe BMP code points from U+00A1–U+FFEF, ~15.92 bits/char). The async encoder tries all four and picks the shortest **transport** length (percent-encoded UTF-8 length for non-ASCII), so base64url can win over Unicode encodings on chat-style surfaces. baseBMP produces ~32% fewer characters than base1k and ~60% fewer than base76 for the same compressed bytes, achieving ~70% smaller fragments than deflate on typical payloads (~6.1x compression ratio for 8k markdown). Full pipeline timing is on the order of ~8–14ms for 8k payloads depending on the wire encoding. The substitution dictionary is served as a static file at `/arx-dictionary.json` so agents can fetch it for local compression; a pre-compressed `/arx-dictionary.json.br` variant is also available. The viewer tries the pre-compressed dictionary first on default ARX-family loads, falls back to the JSON file, and only loads external dictionaries when an ARX/ARX2/ARX3 encode or decode path needs them.
 - `arx2` keeps the arx compression stack but replaces the JSON envelope with a compact tuple envelope and applies `/arx2-dictionary.json` as an overlay before the shared arx dictionary. The viewer tries `/arx2-dictionary.json.br` first for default overlay loads and falls back to JSON. It is emitted with the compact `b` tag (which identifies the codec but does not carry a dictionary version — it implies the current pinned dictionary) and decodes back to the standard envelope before validation/rendering.
-- `arx3` uses the same tuple envelope, overlay dictionary, shared arx dictionary, and brotli bytes as arx2, then allows the dense baseBMP wire to win by decoded visible character length. This deliberately optimizes copyable visible URL length for trusted Unicode-preserving surfaces; it is not a stronger compressed-byte format than arx2.
-- `arx4` keeps the arx3 tuple envelope, overlay dictionary, shared arx dictionary and baseBMP selection rule, and replaces brotli with a deterministic integer context mixer (`arx4-codec.ts`). It is emitted with the compact `e` tag and carries one extra leading payload char, the prior id, naming the priming corpus both sides run before the payload. See `docs/payload-format.md` for the prior ids and the `/arx4-priors.json` asset.
+- `arx3` is decode-only. It used the same bytes as arx2 but scored baseBMP by visible character count, which Discord and WhatsApp then percent-encode or mangle.
+- `arx4` is decode-only. It is the context-mixer codec with the same broken visible-length policy as arx3. Existing `#e` links still open.
+- `arx5` (ARX 4.5) keeps the arx2 tuple envelope, overlay dictionary, shared arx dictionary, and arx4 context mixer, then scores every wire — including baseBMP — by honest serialized transport length. It is emitted with the compact `f` tag and the same prior-id prefix as arx4. See `docs/payload-format.md` for the prior ids, `/arx4-priors.json`, and the chat-safe alphabet research.
 - packed wire mode (`p: 1`) shortens transport keys before compression, then unpacks back to the standard envelope during decode
-- automatic async codec selection tries `arx4 -> arx3 -> arx2 -> arx -> deflate -> lz -> plain`; arx compares packed + non-packed candidates, while arx2/arx3/arx4 use tuple envelopes
+- automatic async codec selection tries `arx5 -> arx2 -> arx -> deflate -> lz -> plain`; arx compares packed + non-packed candidates, while arx2/arx5 use tuple envelopes. Explicit `{ codec: "arx3" }` or `{ codec: "arx4" }` still encodes for back-compat.
 - sync codec selection (used by examples and legacy paths) tries `deflate -> lz -> plain`
-- decode enforces both visible fragment length and decoded payload size ceilings before UI rendering; arx/arx2/arx3 Brotli decompression uses a streaming output cap before final JSON or tuple parsing
+- decode enforces both visible fragment length and decoded payload size ceilings before UI rendering; arx/arx2/arx3 Brotli decompression uses a streaming output cap before final JSON or tuple parsing; arx4/arx5 use the context mixer
 - invalid bundle state is normalized or rejected before renderers mount
 
 ## Zero-retention boundaries

diff --git a/docs/dependency-notes.md b/docs/dependency-notes.md
@@ -33,7 +33,7 @@
 - `@git-diff-view/*` fits review-style diffs better than a generic merge editor for the current viewer. Its pure CSS file is mirrored into `public/vendor/diff-view-pure.css` with a Brotli-compressed `public/vendor/diff-view-pure.css.br` copy by `npm run assets:compress`, and loaded only by the diff renderer; `tests/diff-style-asset.test.ts` keeps those assets in sync with the package copy.
 - `papaparse` handles CSV parsing; CSV rendering uses a native read-only table to avoid a data-grid dependency for the shipped static viewer.
 - `fflate` provides portable deflate/inflate support across iOS Safari and Android Chromium without relying on browser-specific compression streams.
-- `brotli-wasm` provides the arx/arx2/arx3 Brotli compression layer, including streaming decompression used to cap expanded output before allocating oversized decoded payloads.
+- `brotli-wasm` provides the arx/arx2/arx3 Brotli compression layer, including streaming decompression used to cap expanded output before allocating oversized decoded payloads. arx4/arx5 use the integer context mixer instead.
 - `mermaid` renders diagram definitions (flowcharts, sequence diagrams, etc.) to SVG client-side. Dynamically imported within the markdown renderer so it does not affect initial bundle size.
 - `better-sqlite3` provides synchronous SQLite access for the optional self-hosted server mode. Only used by `selfhosted/` code and not bundled into the static frontend export.