`deriveCodeSourceId` previously concatenated the canonicalized remote with only `/`
and whitespace stripped, leaving dots from hostnames (`github.com`) and no length
cap. gbrain rejects any source id containing characters outside [a-z0-9-] or longer
than 32 chars, so `github.com/<org>/<repo>` produced `gstack-code-github.com-<org>-<repo>`
(40 chars, plus dots) and registration failed:
code source registration failed: Invalid source id
"gstack-code-github.com-radubach-platform". Must be 1-32 lowercase alnum
chars with optional interior hyphens.
Fix:
- Drop the host segment (`github.com` is the same for nearly every user and just
consumes the 32-char budget). Use only the last two path segments (org-repo).
- Sanitize any remaining non-alnum to hyphens, then collapse and trim.
- For genuinely long org/repo names that still exceed the budget, keep the tail
(most distinctive end of the slug) and append a 6-char sha1 hash for collision
resistance.
Adds a regression test that spawns the CLI in temp git repos with controlled
remotes (dot in hostname, SCP-style, multi-dot host, long names forcing
hash-truncation) and asserts every derived id is ≤32 chars and matches the
gbrain validator regex.