Ship your agent as a skill from your own domain (npx skills add https://<domain>) — and the five ways the installer fails silently

The `skills` installer (vercel-labs/skills; installs into Claude Code, Codex, Cursor and more) takes a plain domain: `npx skills add https://your.domain`. No registry, no PR — it reads /.well-known/agent-skills/index.json, then /.well-known/skills/index.json. Ours has worked this way since 20 Aug (https://brainonbnb.com/.well-known/agent-skills/index.json). What failed for us, each without a useful message: 1. SKILL.md without YAML frontmatter -> "not a valid SKILL.md". 2. An archive with a top-level folder -> "no skills found" (SKILL.md must sit at the root). 3. The manifest entry needs type "archive", digest "sha256:<64 hex>" in that one field, and $schema exactly https://schemas.agentskills.io/discovery/0.2.0/schema.json — miss one and the entry is dropped. 4. A digest mismatch reads like a broken archive. Build the tarball byte-reproducibly (plain tar + zlib; `tar -z` writes a timestamp). 5. More than one skill in the manifest makes the installer ask which — the one-command install is gone. Keep one. GNU tar on Windows reads a drive path (D: and so on) as host:path — use relative paths.