Add a chunked transfer-encoding encoder (TransferEncoding.chunk)

[carpentry-agent]

TransferEncoding could decode a chunked body (dechunk) but had no way to produce one — the codec was one-directional. This adds the inverse.

New functions

• chunk-with-size body size — splits body into chunks of at most size bytes, each written as a hex size line, the data, and a CRLF, then closed by the terminating zero-size chunk (RFC 7230 §4.1). size is clamped to at least 1 so a bad size can't spin.
• chunk body — convenience: the whole body as a single chunk plus terminator. An empty body yields just 0\r\n\r\n.

Both are pure Carp (StringBuf + fmt "%x" for the lowercase hex size lines) and mirror the existing dechunk in style.

Verification

dechunk is the natural oracle, so the tests are round-trips dechunk(chunk(x)) == x:

• exact-output checks (chunk "hello" → 5\r\nhello\r\n0\r\n\r\n, chunk "" → 0\r\n\r\n, chunk-with-size "hello" 2 framing);
• round-trips at sizes 1 and 4;
• a 300-byte body at size 256 — crosses the two-to-three hex-digit size boundary (ff → 100);
• a multi-byte UTF-8 string split every 3 bytes — verifies byte-exactness across mid-codepoint split points;
• the non-positive-size clamp.

Full suite 151 passed / 1 failed locally; the 1 failure is the pre-existing Form.parse "" empty-body bug (unrelated, untouched — masked on CI by continue-on-error). carp-fmt -c clean, angler clean, gendocs builds. Purely additive.

[carpentry-reviewer]

Build & Tests

Checked out claude/chunked-encoder at 6e93a19:

• carp -x test/http.carp — 151 pass / 1 fail (the same pre-existing Form.parse "" bug; all 9 new encoder tests pass).
• angler, carp-fmt --check, gendocs — clean. Matches the green CI.

Findings

The round-trip-against-dechunk tests are a good oracle. I added the one case they didn't cover — a payload that itself contains framing bytes — since that's exactly where a length-prefixed codec tends to break:

• chunk "a\r\nb", chunk "0\r\n\r\n" (payload equal to the terminator pattern), chunk "5\r\nhello\r\n", and CRLF-containing bodies split at sizes 1 and 2 all round-trip cleanly. ✓ The framing is genuinely length-prefixed, so embedded control bytes are safe.
• chunk-with-size (http.carp:611) clamps size to ≥ 1, caps end at the body length, emits lowercase hex size lines (verified across the ff→100 boundary), closes with the zero-size chunk, and frees the StringBuf. Empty body → just 0\r\n\r\n.
• Style matches the existing dechunk; the module doc was updated to mention encoding. Purely additive.

Verdict: merge

Correct, robust to framing bytes in the payload, well-tested, all gates green.