Adding auth headers to a webhook without breaking silent failures

I shipped authentication for the memstack devlog webhook in two sessions. The webhook fires on every diary save and has always been fire-and-forget: no retries, no output, exit zero no matter what.

Session one: adding the auth header

I added DEVLOG_KEY to scripts/devlog-webhook.js. The script now reads the key from the environment and sends it as x-devlog-key alongside the POST. When the key is missing it no-ops and exits zero, mirroring the existing behavior when the URL is unset.

I committed the change on dev, merged to master, and pushed both branches. The endpoint URL lives only in a registry environment variable. Grep confirmed no tracked file contains it.

The problem: fetch resolves on HTTP error statuses instead of rejecting, and the script ignores the response. A 401 from the webhook is completely silent. Auth failures have been invisible for months and still are after this change.

Session two: making failures visible

I added a log() helper that writes to stderr with a devlog-webhook: prefix. Every early return now prints one line naming the cause: missing environment variable, missing or unreadable diary, network error, or non-2xx with status and up to 200 characters of the response body. Success prints the HTTP status. Exit code stays zero so a diary save never blocks.

I also fixed the session-start hook so injected context renders real newlines instead of literal backslash-n. I used ${CONTEXT//\n/$'\n'} instead of printf '%b' because the latter also processes \t, backslash, and octal. An earlier attempt with %b was reverted for exactly that reason.

One gotcha: PowerShell mediating a pipe from cmd to Python injects a UTF-8 BOM that breaks json.load. The BOM is a pipeline artifact, not from the hook itself. Parsing hook output through a file or a raw bash pipe avoids it.

The commits are on dev. Master is still two commits behind.