Release 0.6.2: external-api hosts, bounded WS writes, DoConcurrent workers, long error bodies, license

[UTXOnly]

Fixes #14, #15, #16, #17, #18. Bumps to 0.6.2 (0.6.1 is tagged). No API-incompatible changes — gorelease -base=v0.6.1 reports only two compatible additions (WSWriteTimeout, ErrWSWriteTimeout).

Changes

#14 — DoConcurrent started n goroutines even with a bounded maxInFlight
The semaphore is replaced by a worker pool of min(n, maxInFlight) goroutines fed by an atomic counter; the result buffer is sized to the workers rather than n. Results stay index-ordered; cancellation still returns the results collected so far plus ctx.Err(), after which workers take no further indices and never block on the result channel. Unbounded mode (maxInFlight <= 0) is unchanged except that a context already cancelled on entry no longer invokes fn (bounded mode already behaved that way).

#15 — WebSocket writes could block past context deadlines and hang Close
writeMu becomes a 1-slot writeSem channel so a waiter can honor its context. Every data frame is written under the sooner of the caller's deadline and the new WSWriteTimeout option (default 10s; <= 0 uses the default). A write that times out fails the connection with an error wrapping ErrWSWriteTimeout — Messages() closes, Err() reports it, same path as ErrWSSlowConsumer; the caller whose own deadline cut the write gets context.DeadlineExceeded. A caller that gives up waiting for the slot gets ctx.Err() and the connection stays healthy. Close sends the close frame as a bounded WriteControl, skips it if a command write is in flight, closes the socket (unblocking a stuck writer), and is documented to return within about WSWriteTimeout + 5s even when the peer is not reading. Control frames (ping/pong/close) keep using gorilla's WriteControl, which serializes itself and is safe alongside a data write.

#16 — APIError lost Code/Message/Details when a valid error body exceeded 512 bytes
Structured fields now decode from up to 64 KiB of the body; RawBody remains the first 512 bytes; bodies over 64 KiB are read no further and are not decoded. The three production body shapes from #13 are parsed exactly as before.

#17 — No license
MIT LICENSE. README license section notes that the vendored openapi.yaml / asyncapi.yaml are Kalshi's published specifications and are not covered by it.

#18 — Default to Kalshi's recommended hosts
external-api.kalshi.com (REST) and external-api-ws.kalshi.com (WS) are now the defaults; the shared api.elections.kalshi.com remains supported via BaseURL / WSHost. Signing is unaffected (the signed message excludes the host). The WebSocket example maps external-api.kalshi.com in BASE_URL to the -ws host, since the recommended hosts differ per protocol. README, example READMEs, AGENTS.md, and CHANGELOG describe the change and overrides.

Tests

20 new tests, all under -race:

• DoConcurrent: goroutine growth < 100 at n=10000, maxInFlight=4; limit above n; cancellation while all workers are blocked (returns promptly, no new indices taken, goroutines settle); n == 0.
• WebSocket: option storage; a caller whose ctx ends while waiting for the write slot returns ctx.Err() with the connection untouched; 20 concurrent callers half pre-cancelled; write timeout as a terminal error (16 MB payload to a non-reading peer); a caller deadline cutting a write; a blocked writer not holding other callers; bounded Close with a stuck writer and with a pre-jammed socket.
• APIError: long valid bodies in all three shapes (fields populated, RawBody is a 512-byte prefix); malformed/truncated long JSON; a counting reader asserting the read is bounded at 64 KiB (exactly-at-limit decodes, one byte over does not).
• Hosts: default REST request URL; the signed path is identical across the external-api, shared, and demo base URLs; default WS dial URL (option resolution factored into wsConfig so it can be asserted without dialing).

Verification

gofmt, go vet, staticcheck, go mod tidy no-op, go build, go test -race -count=1 -shuffle=on ./... (3× full; 10× on the new timing-sensitive tests), and gorelease -base=v0.6.1 -version=v0.6.2 all clean locally. govulncheck reports only Go standard-library advisories present in the local go1.26.0 toolchain (fixed in 1.26.6); identical on main.

Review notes

• One assertion in the new TestWS_Close_BoundedWhenSocketFull originally required the close frame's control write to time out; whether a 6-byte frame fits into a jammed send buffer depends on kernel drain timing, so it now asserts the bound strictly and accepts nil-or-timeout for the frame write.
• The host change is filed as a patch under ### Changed since both hosts work and no API changed. If a default-endpoint swap should count as breaking (egress allowlists), this should become ### Breaking + 0.7.0.

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