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fix(arx): account for chat-safe transport when selecting ARX wire form #15

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Merged
baanish merged 1 commit into from
Mar 20, 2026
Merged

fix(arx): account for chat-safe transport when selecting ARX wire form #15

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14 changes: 10 additions & 4 deletions src/lib/payload/fragment.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -36,17 +36,23 @@ type CandidateFragment = {
transportLength: number;
};

const CHAT_SAFE_ASCII_FRAGMENT_CHARS = /^[A-Za-z0-9\-._~=#]+$/;

/**
* Computes the serialized length of a fragment value as it would appear in a
* URL after browser percent-encoding of non-ASCII characters.
* Each non-ASCII UTF-8 byte is encoded as %XX (3 chars per byte).
* Computes the serialized length of a fragment value after conservative transport escaping.
*
* We count non-ASCII code points by their UTF-8 percent-encoded size, and we also treat
* ASCII punctuation outside the URL-unreserved fragment subset as escape-prone because many
* chat/link surfaces rewrite those characters even when a browser would accept them in-place.
* This keeps auto-selection aligned with the product's chat-safe fragment goal, allowing the
* `B.` base64url ARX wire shape to win when punctuation-heavy base76 would grow after sharing.
*/
function computeTransportLength(value: string): number {
let len = 0;
for (let i = 0; i < value.length; i++) {
const cp = value.codePointAt(i)!;
if (cp < 128) {
len += 1;
len += CHAT_SAFE_ASCII_FRAGMENT_CHARS.test(value[i]) ? 1 : 3;

@chatgpt-codex-connector chatgpt-codex-connector Bot Mar 20, 2026

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P1 Badge Avoid preferring over-budget B. fragments over valid base76

This 3x penalty means encodeEnvelopeAsync(..., { codec: "arx" }) can now pick the chat-safe B. wire form even when it makes the real fragment exceed the 8,000-character limit that callers still enforce with hash.length - 1 (for example in createGeneratedArtifactLinkAsync). I reproduced this with a packed markdown payload of about 5,900 repeated bullet lines: the base76 fragment is 7,985 chars and would still work, but its computed transport length becomes 10,159 here, so the encoder instead selects an 8,331-char B. fragment and link creation rejects it. That is a user-visible regression for large payloads near the fragment budget.

Useful? React with 👍 / 👎.

} else if (cp < 0x800) {
len += 6; // 2 UTF-8 bytes → %XX%XX
} else if (cp < 0x10000) {
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22 changes: 22 additions & 0 deletions tests/arx-codec.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -296,6 +296,28 @@ describe("arx fragment round-trip", () => {
expect(autoHash).toContain(`v1.arx.${getActiveDictVersion()}.`);
});

it("async arx selection can choose the chat-safe base64url wire form", async () => {
const bigEnvelope: PayloadEnvelope = {
...envelope,
artifacts: [
{
id: "doc",
kind: "markdown",
filename: "doc.md",
content: [
"# Chat-safe ARX",
"",
...Array.from({ length: 120 }, (_, index) => `- item ${index}: The quick brown fox jumps over the lazy dog.`),
].join("\n"),
},
],
};

const autoHash = await encodeEnvelopeAsync(bigEnvelope, { codec: "arx" });
expect(autoHash).toContain(`v1.arx.${getActiveDictVersion()}.B.`);
});


it("decodes arx fragments when unicode payload chars are percent-escaped", async () => {
const hash = `#${await encodeEnvelopeAsync(envelope, { codec: "arx" })}`;
const escapedHash = hash.replace(/[^\x00-\x7F]/g, (char) => encodeURIComponent(char));
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