fix(publisher): document --algorithm for ECDSA login and fix validate --help (#1519)

Two real defects, plus the CLI reference claims that go with them.

## 1. ECDSA P-384 login instructions cannot work

Every "ECDSA P-384" tab ran the *identical* command to the Ed25519 tab.
Since `--algorithm` defaults to ed25519
([login.go:100](https://github.com/modelcontextprotocol/registry/blob/main/cmd/publisher/commands/login.go#L100)),
a 96-hex key is rejected outright. Verified against a freshly generated
P-384 key:

```
$ mcp-publisher login dns --domain=example.com --private-key=$KEY
Signing in process using key algorithm ed25519
Error: failed to get token: failed to sign timestamp: invalid seed length: expected 32 bytes, got 48

$ mcp-publisher login dns --algorithm ecdsap384 --domain=example.com --private-key=$KEY
Signing in process using key algorithm ecdsap384
Expected proof record:                      # works
```

`--algorithm` is registered at
[login.go:129](https://github.com/modelcontextprotocol/registry/blob/main/cmd/publisher/commands/login.go#L129)
and described correctly by the CLI's own help, but `grep -rn algorithm
docs/` had **zero** hits for it. Anyone following the ECDSA path in the
docs hit that error with nothing to tell them why.

Fixed at all four in-process ECDSA sites (2 in `authentication.mdx`, 2
in `cli/commands.md`), with a note that cloud signing providers derive
the algorithm from the key itself so the flag does not apply to them.

## 2. `mcp-publisher validate --help` was broken

```
$ mcp-publisher validate --help
Unknown command: validate
...
Use 'mcp-publisher <command> --help' for more information about a command.
```

It printed the very instruction that had just failed. `main.go`
intercepted `--help` for all subcommands and called `printCommandHelp`,
whose switch had no `validate` case — making `ValidateCommand`'s own
help block
([validate.go:120-129](https://github.com/modelcontextprotocol/registry/blob/main/cmd/publisher/commands/validate.go#L120))
unreachable.

Rather than paste a third copy of the help text, `printCommandHelp` now
returns whether it handled the command, and the caller falls through to
normal dispatch when it did not. Commands own their own `--help`, and
any future command with this shape works automatically.

| Command | Before | After |
|---|---|---|
| `validate --help` | `Unknown command`, exit 0 | prints its help, exit
0 |
| `publish --help` | works | works |
| `init -h` | works | works |
| `bogus --help` | `Unknown command`, exit 0 | `Unknown command`, **exit
1** |

## 3. CLI reference corrections

- **`--registry` is not global.** It exists only on `login`; other
commands read the URL from the stored token. `publish --registry=URL`
silently treats the flag as the `server.json` path.
`cmd/publisher/README.md` had exactly this broken example.
- **`--token` was undocumented** despite `github-actions.mdx:123`
depending on it. Now documented, noting it is `login github` only.
- **`init` takes no flags** and does not prompt; it writes `TODO:`
placeholders. The reference said `init [options]` and "Prompts for
missing required fields".
- **Refreshed the `--help` transcript** in `quickstart.mdx`, which
listed only 4 of 6 commands. Now byte-for-byte identical to real output
(diffed).
- **Added `validate`** to the command list in `cmd/publisher/README.md`.

## Verification

`go build` and `go test ./cmd/...` pass. All four help paths exercised
with exit codes checked. The 23 `goconst` findings in `validate_test.go`
are pre-existing — identical count on pristine `main`, none in
`main.go`. Quickstart transcript diffed against real output.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

cmd/publisher/README.md

@@ -14,9 +14,12 @@ make publisher
 make dev-compose  # Start local registry
 ./bin/mcp-publisher init
 ./bin/mcp-publisher login none --registry=http://localhost:8080
-./bin/mcp-publisher publish --registry=http://localhost:8080
+./bin/mcp-publisher publish
 ```
 
+`publish` takes the registry URL from the token saved by `login`, so it accepts no `--registry`
+flag — passing one would be read as the `server.json` path.
+
 ## Architecture
 
 ### Commands
@@ -24,6 +27,7 @@ make dev-compose  # Start local registry
 - **`login`** - Handle authentication (github, dns, http, none)
 - **`publish`** - Validate and upload servers to registry
 - **`status`** - Update server lifecycle status (active, deprecated, deleted)
+- **`validate`** - Validate server.json without publishing
 - **`logout`** - Clear stored credentials
 
 ### Authentication Providers

cmd/publisher/main.go

@@ -27,10 +27,12 @@ func main() {
 		os.Exit(1)
 	}
 
-	// Check for help flag for subcommands
+	// Check for help flag for subcommands. Commands without an entry in
+	// printCommandHelp handle --help themselves, so fall through to dispatch.
 	if len(os.Args) >= 3 && (os.Args[2] == "--help" || os.Args[2] == "-h") {
-		printCommandHelp(os.Args[1])
-		return
+		if printCommandHelp(os.Args[1]) {
+			return
+		}
 	}
 
 	var err error
@@ -81,7 +83,10 @@ func printUsage() {
 	_, _ = fmt.Fprintln(os.Stdout, "Use 'mcp-publisher <command> --help' for more information about a command.")
 }
 
-func printCommandHelp(command string) {
+// printCommandHelp prints help for a specific command and reports whether it had
+// an entry here. Commands without one parse --help themselves, so the caller
+// should fall through to normal dispatch when this returns false.
+func printCommandHelp(command string) bool {
 	switch command {
 	case "init":
 		_, _ = fmt.Fprintln(os.Stdout, "Create a server.json file template")
@@ -165,7 +170,8 @@ func printCommandHelp(command string) {
 		_, _ = fmt.Fprintln(os.Stdout, "You must be logged in before updating status. Run 'mcp-publisher login' first.")
 
 	default:
-		fmt.Fprintf(os.Stderr, "Unknown command: %s\n", command)
-		printUsage()
+		return false
 	}
+
+	return true
 }